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I recently spent several days reading (books) about EFI idle tuning and improving my engine's idle quality. I finally achieved, what I consider, an excellent idling engine...but it wasn't easy. In fact, I believe the Holley HP/Dominator ECU is more sensitive to idle tuning (idle algorithm), than the Commander 950 is; meaning it's easier to achieve a good idle with the C950. I tried to disregard what I thought I knew about idle tuning and start with a fresh mindset...I'm glad I did. Every engine will idle slightly different and the engine combination (components) will affect the idling characteristics, especially the camshaft. These ECU parameters influence the idle quality:
Target Idle Speed RPM
Increasing the idle RPM provides a smoother idle. This doesn't mean your engine has to idle at 1000 RPM, however, don't expect a race engine with a radical camshaft to idle at 700 RPM. Generally, the bigger the camshaft the more idle RPM it needs. Most mild performance engines should idle well at 700-800 RPM and most potent street performance engines should idle well at 800-900 RPM. Serious race engines with radical camshafts will need to idle at 900-1000+ RPM, due to the camshaft's tight LSA which causes a high overlap period (not efficient at idle & low RPM). Also, ensure the Target Idle Speed RPM scale is properly programmed. If the hot engine idles in between two temperature cells on the Target Idle Speed scale, set the temperature cell before & after the target idle, to the same RPM; so the ECU doesn't vary the idle speed.
Target Air/Fuel Ratio
Modern cylinder heads with efficient combustion chambers will idle leaner at 14.7-15.2 AFR and require less 20°-22° idle Timing (LINK) with moderate performance camshafts. These newer generation efficient combustion chambers require a lot less overall AFR & Timing. Most older traditional high performance engines will idle well with a target air/fuel ratio between 13.8-14.2 (depending on camshaft specs). This surprised me, and I wasn't comfortable with it at first, because I thought the idle should be leaner at a stoichiometric 14.7:1 AFR. However, when I tried it, my engine responded so favorably, especially when I shifted it in gear. This became one of the three most significant aspects of my idle quality improvement (the other two being timing advance & Fuel Table tuning). This isn't as detrimental to fuel economy as one might think, because at idle, there are less injection events (engine cycles) over time, than at higher RPM. Sequential fuel injection MPFI engines can idle lean at 14.7:1 AFR, even with a street performance camshaft in Closed Loop. Although this requires a relatively wider lobe separation angle such as 114° (LINK - scroll to end). I've found this lean idle AFR is more prevalent with high CFM airflow/port velocity cylinder heads and properly angled fuel injectors (less X-Tau fuel wall wetting - LINK/LINK). Remember to also check the idle in gear, and allow the engine to idle for at least a minute with each change. (LINK)
RPM & kPa Axis Configuration
When an engine is idling, there's a 'target idle cell' on the Fuel & Timing Tables. It's important to identify this single cell, in order to properly configure the RPM (X) axis & kPa (Y) axis. Ideally, the target idle cell should be in the center of the RPM & kPa range the engine idles in. Some engines exhibit better idle stability than others, as seen on the Fuel & Timing Tables. The goal is to configure the idle area so the idle has equal range above & below the target value. Fuel & Timing Tables should have three RPM columns and three kPa rows; one column/row above & below the target column/row. The values programmed above & below the target, depend on how the engine idles and the resolution of the Fuel & Timing Tables (e.g. 16x16 vs. 31x31). Typically, the RPM axis (idle area) has increments of 100-150 RPM, and the kPa axis (idle area) has increments of 2-8 kPa. Adding idle resolution to the kPa (Y) axis can resolve issues with a radical camshaft and/or a forced induction application (with naturally less resolution in the off boost regions of the table). Remember to check the idle in gear, to verify the kPa axis configuration above idle, is acceptable. (LINK)
Base Fuel Table
Sniper/Avenger/Terminator/Terminator X/HP/Dominator EFI users, disregard the following Commander 950 EFI references.
Most people I help, don't know how to tune the idle area of the Fuel Table especially the Commander 950 EFI. It has a big impact on the idle stability. The Base Fuel Table should not be totally flat (except in the Fuel Graph); meaning you can't have the same numbers in the idle area. Unlike the Base Timing Table & Target A/F Ratio Table, which should be flat in the idle area. Below are sample Fuel Table idle tuning scenarios for the Commander 950 EFI. The Fuel Table values are a pulse-width, as opposed to the Sniper/Avenger/Terminator/Terminator X/HP/Dominator Base Fuel Table, which is in pounds-per-hour (LBS/HR). This means the Commander 950 Fuel Graph looks like the engine's torque curve (LINK).
The Holley Sniper/Avenger/Terminator/Terminator X/HP/Dominator EFI LB/HR Fuel Graph looks like the engine's horsepower curve.
The Holley Sniper/Avenger/Terminator/Terminator X/HP/Dominator EFI VE % Fuel Graph looks like the engine's torque curve.
The bold numbers indicate idling with no load (13) & idling in gear and/or accessories on (15). The surrounding cells direct the engine idle back to the target idle cell (center). Study the diagonal pattern of the idle numbers; that's the secret to good Commander 950 Fuel Table idle tuning. Notice how the values increase with higher load & less RPM, and decrease with lower load & more RPM. Example (Commander 950 EFI):
MAP
62...16...15...14
56...15...14...13
50...14...13...12
44...13...12...11
.....700..800..900 RPM
The Fuel Table example above is a good one, however, it illustrates the idle segment of a Commander 950 Fuel Table with large injectors. On Commander 950 Fuel Tables, smaller numbers mean larger injectors, and larger numbers mean smaller injectors. Therefore, if your idle values (numbers) are larger than what's illustrated above (typical injector sizing), then the number pattern should change in increments of two or maybe even three. Example (Commander 950 EFI):
MAP
62...31...29...27
56...29...27...25
50...27...25...23
44...25...23...21
.....700..800..900 RPM
Since the new Avenger/Terminator/HP/Dominator ECUs self-tune, why does the idle area of the Base Fuel Table need to be adjusted? Because the Learn function can only self-tune to the Target Air/Fuel Ratio Table in a floating 3x3 cell (9 block) pattern; and it does so very well. When the Learn Table self-tunes, it's adjusting the entire idle area the same amount; just like it's supposed to. In other words, the Base Fuel Table is responsible for idle quality, and the self-tuning is responsible for WBO2 compensation. So the idle area of the Base Fuel Table needs to be blended smooth (using the Fuel Graph) to promote a smooth idle, for the same aforementioned reasons. When Holley engineers create the base calibrations, it's impossible to know exactly where anyone's engine will idle on the Base Fuel Table. The engine has to be idling to tune the idle. Therefore, the base calibrations must gradually increase the lb/hr values (MAP & RPM) for the Learning to self-tune. The Avenger/Terminator/HP/Dominator EFI Base Fuel Tables use "lbs/hr" unit of measure, so the number incrementation won't be as equally spread as the C950. The point is to manipulate the engine to idle well, by having a smooth Base Fuel Table.
• Ensure the Base Fuel Table is smooth by viewing & blending the Fuel Graph. It's very important to have a smooth Fuel Graph.
One aspect of viewing the Fuel Graph: It's better to zoom in, by highlighting segments of the Base Fuel Table (left click & drag), and click "Graph".
This method offers much greater detail. Looking at the entire "Fuel Graph" will almost always look smooth, because it's not as magnified.
TIP: When the Fuel Graph is smooth, click "Conversion" (VE% Conversion mode) and continue smoothing the general contour of the VE Fuel Graph.
• If you'd like to manually tune the Base Fuel Table (even while the engine is running), read below:
Left click & drag to select a group of cells, then use the CTRL & Arrow keys (▲►▼◄) to change the highlighted cell values.
The ▲ & ▼ arrow keys adjust the Base Fuel Table slowly (one tenth at a time). The ◄ & ► arrow keys adjust it rapidly.
Or you can left click & drag a group of highlighted cells, and right click "Offset Selected" to adjust the entire cell group.
• When the engine is tuned & running well, you should decrease the Closed Loop and Learned Compensation Limits % to lock in a good tune.
I decreased my Learned Compensation Limits to 2% in the idle area (10% elsewhere). My Closed Loop Compensation Limits are 50% or less.
When the Learn Table values stop making significant changes, the ECU is finished self-tuning. (LINK - Read this Learn Table thread, especially posts # 2, # 6 & # 11.)
http://forums.holley.com/showthread....2523#post62523 (Holley EFI Tuning Tips & Information)
https://www.youtube.com/watch?v=y17MClF7SYA (Base Fuel Table/Fuel Graph Tuning - Part 1)
https://www.youtube.com/watch?v=aRn3A5_ecpo (Base Fuel Table/Fuel Graph Tuning - Part 2)
Closed Loop/Learn Compensation ±
ECUs without Learning capability will have a Closed Loop Compensation Limit of around ±25%, and must be tuned so the ECU is subtracting about 5% from the Fuel Table. With a limit of only ±25%, the initial tuning procedure will most likely need to be repeated each time the tuning is applied to the Fuel Table. You won't notice the ECU subtracting fuel, but you can notice it adding fuel. For initial tuning purposes, allow the maximum value in the idle area, due to coolant & air temperature modifiers. ECUs with Learning capability will have a virtually infinite Closed Loop Compensation Limit; as much as ±999%. The reason why, is so the ECU doesn't need to repeat the entire modification to the Base Fuel Table (if the O2 Compensation was limited), every time it returns to idle or any other area for that matter. The Learn Table modifies the Base Fuel Table by applying its Learned amount to the Base Fuel Table values.
• In some stubborn cases, a better idle may be attained by limiting the amount of Closed Loop Compensation or Learning, added or subtracted from the idle area. Also, large duration (race) camshafts will exhibit a fluctuating AFR/false lean condition at idle & low RPM, due to their significant amount of overlap, and/or a WBO2 sensor near the end of an open exhaust pipe. To rectify this, enter Closed Loop Parameters and set the "Enable RPM to Enter Closed Loop" high enough to ignore this condition. You'll then need to manually tune the idle area in Open Loop mode.
• Also, the Advanced Control (1-5) sets how fast the Closed Loop control operates. 1 is the slowest and 5 is the fastest. (The Avenger & Terminator hand-held controller calls this the "Closed Loop Speed".) This depends heavily on where the WBO2 sensor is located in the exhaust system. The further away the WBO2 sensor is (away from the engine), the lower the number should be. If Advanced Control 4 or 5 is selected, one must ensure the ECU isn't oscillating the Closed Loop operation. Viewing a datalog is helpful. I experienced a condition where the actual AFR often "lagged" momentarily, behind the Target AFR. I fixed it by changing the Closed Loop Advanced Control to 5. My WBO2 sensors are located in full-length header collectors. Sometimes it's best to start at a lower value, especially with a fresh base calibration.
• When the engine is tuned & running well, you should decrease the Closed Loop and Learned Compensation Limits % to lock in a good tune. (LINK) I decreased my Learned Compensation Limits to 2% in the idle area (10% elsewhere). My Closed Loop Compensation Limits are 50% or less. When the Learn Table values stop making significant changes, the ECU is finished self-tuning.
Ignition Timing Advance
First, ensure the ignition timing is synchronized (LINK). The Base Timing Table must be flat in the idle area, meaning it's the same value in the entire idle area (especially if using Idle Spark Control). Modern cylinder heads with efficient combustion chambers will idle leaner at 14.7-15.2 AFR and require less 20°-22° idle Timing (LINK) with moderate performance camshafts. These newer generation efficient combustion chambers require a lot less overall AFR & Timing. Most street performance engines will idle well with 15°-25° of timing advance. (Stock cam - 20°, performance cam - 25°, radical cam - 30°). The exact amount depends heavily on the camshaft specifications. Generally, tighter LSA - lobe separation angles (overlap) and larger lobe duration figures, require more timing advance at idle. 106°-108° is considered a tight LSA (idle quality suffers with less idle vacuum), 108°-110° is moderate, 110°-112° is moderately wide, and 112°-114° is wide (idle quality improves with more idle vacuum). One must pay close attention to how much timing advance is used at idle. Resist the urge to use too much; I've made this mistake in the past. Advancing the timing, offers better fuel efficiency and raises the idle speed, however, excessive timing creates an unstable idle speed due to the engine having too much torque at idle (Idle Spark control becomes ineffective). Retarded timing lowers the idle speed, decreases engine torque and increases the coolant temperature. Excessively retarded timing also causes the exhaust headers to glow red hot. Remember to check the idle in gear, to verify the amount used is also acceptable. (LINK)
Idle Spark Control Tuning
The Idle Spark Control basically helps stabilize the idle speed by manipulating the timing (quickly increasing & decreasing in accordance to RPM). The idle quality must be well tuned before adjusting these two parameters. If the idle is well tuned (fuel & IAC), the Idle Spark PID control can actually help determine the optimum timing advance at idle (LINK & LINK). It may help to datalog various P & D combinations (name the datalog by the two numbers to decipher them), and look for the straightest RPM line. This is because you can't watch the idle RPM on the Data Monitor, since they change too fast and the tachometer usually isn't an accurate enough indicator of idle stability. I've found values of 30-40 (P Term) & 50-60 (D Term) are a good start with Holley EFI systems.
P & D Definitions - Excerpt from Holley EFI manual:
• Proportional Term – The speed at which the ignition timing is varied to maintain target idle.
• Derivative Term – Eliminates the overshoot.
IAC Control Tuning
The PID terms must be fine tuned to each particular engine. Start with all three PID parameters at 10. Tune the Proportional first, the Derivative second, the Integral last, then fine tune the three together. Temporarily disable the Idle Spark Control while tuning the idle PID parameters, and ensure the Fuel Map is well tuned in the idle area. It may help to datalog various PID combinations (name the datalog by the three numbers to decipher them), and look for the straightest RPM line. This is because you can't watch the idle RPM on the Data Monitor, since they change too fast, and the tachometer usually isn't an accurate enough indicator of idle stability. Of course, you don't have to datalog the number combinations that obviously make it idle worse. Typically, slower IAC control promotes better idle stability.
PID Definitions - Excerpt from the Holley EFI manual:
• P Term – (Proportional) Speed/gain of the system when there is a large deviation in the target idle speed. Raising this value increases the speed at which the IAC moves in order to remove target idle speed error. If this value is too high for a specific application, the IAC position will oscillate (be out of control), and cause the engine speed to surge up & down. If the value is too low for a specific application, the IAC will be slow to react to quick changes in idle speed deviation. However, it is much better for this term to be conservatively slow, rather than too fast.
• I Term – (Integral) speed of the system when the engine speed is near the target idle speed. Raising this value increases the speed at which the IAC moves when the engine speed is close to target idle speed. If this value is too high for a specific application, there may be “too much IAC activity” around the target idle speed. If the value is too low for a specific application, the IAC will be slow to react to changes near target idle speed. However, it is much better for this term to be conservatively slow, rather than too fast.
• D Term – (Derivative) Higher derivative terms reduce the tendency of idle speed overshoot. Smaller derivative terms slow down the IAC movement as target idle speed is approached.
http://forums.holley.com/showthread....neral-IAC-Info (General IAC Information - Read "IAC NOTES")
IAC Counts or Position (%)
The throttle blades must be set so the engine is breathing sufficient air on its own (without excessive IAC intervention), for idling & starting. The IAC motor/valve is supposed to regulate the idle airflow to help maintain the idle speed. IAC motors have an IAC Position range of either 0-255 counts or 0%-100% (each 1% is the equivalent of 2.55 counts). The throttle blades (idle speed screw) is often set to position the IAC motor at 8-12 counts or 15%+ at hot idle. I've found this to be too much IAC control when it's closing (toward zero). I prefer to further open the throttle blades to achieve a IAC position of 3 counts or 5% at hot idle. This only allows a minute amount of airflow reduction, which always seems to promote a more steady idle speed and improve starting. Remember to perform another TPS Autoset, whenever you adjust the idle speed screw on the throttle body. In the Idle ICF, the "Target Idle Speed (RPM)" must be programmed to the desired RPM speed at hot idle. If the idle speed screw is unscrewed too far, the engine is inhaling air from an additional source - vacuum leak. Ensure the proper type of Advanced Idle Control is selected in Idle Settings. "Slow" may provide the best idle quality. (LINK)
FYI: The Commander 950 EFI system uses IAC Position Counts, not IAC Position %, so don't try copying the Commander 950 IAC values. IAC motors have an IAC position range of either 0-255 counts or 0%-100% IAC Position (each 1% is the equivalent of 2.55 counts).
Injector End Angle
I also spent some time tuning the injector end angle timing. ECUs have different end angle software parameters, so there's an excerpt of how Holley does it below. I like the idea of injecting fuel a little earlier during the intake stroke. The end angle has a diminishing effect as the injector duty cycle reaches 90% (since the injectors are "on" for most of the engine cycle), however, it's nice to tune this for optimum idle quality and low to mid RPM torque. Torque, economy, emissions & idle quality are all effected by the injector timing. The optimum value depends on the engine RPM & load. To notice a difference, the end angle must be adjusted in large increments, such as −45° or −90°. The injection timing can be plotted on paper, if the user knows the injector duty cycle in question, and the intake valve opening (°BTDC) & closing (°ABDC) events. Good technical description from Motec: LINK.
• Excerpt from the Holley EFI manual:
"Injector End Angle - This is the crankshaft angle in degrees when the injectors will finish their injection event. A value of 0° will end the injection event at BDC (Bottom Dead Center) before the compression stroke. A negative value moves the event before BDC, and a positive value moves the event after BDC. There could be some improvements in cylinder to cylinder fuel distribution by tuning this parameter. If modifying, it is best to move this value in a negative direction to start."
• For reference (in Holley EFI software), a 0.0° Injector End Angle value, ends the injection event at BDC (Bottom Dead Center) of the intake stroke, before the compression stroke. This is 540° in the four stroke cycle. A negative value moves the injection event before BDC, and a positive value moves the injection event after BDC. So a −180° Injector End Angle value will end the injection event at TDC (Top Dead Center) of the intake stroke (as the intake valve is opening). Obviously, a −90° Injector End Angle value will end the injection event in the middle of the intake stroke.
FYI: The Holley V4 EFI software/ECU firmware now has much more sophisticated Injector End Angle/Phasing parameters. We discussed it in depth HERE (MPFI engines only).
Injector Pulse-Width
It's important to use the proper size fuel injectors. Injectors that are too large for your application, won't idle well due to low pulse-width operation. Don't decrease fuel pressure in order to increase pulse width times at idle. Decreasing fuel pressure results in less than optimum injector spray patterns. Holley's older EFI documents suggests the pulse-width at hot idle shouldn't be lower than 1.7 msec (which won't be an issue when using the appropriate size injectors), and that it shouldn't fluctuate more than .3 msec. However, the Chief EFI Engineer at Holley stated the new HP & Dominator ECU injector drivers are capable of running the pulse-width at hot idle down to 1.3-1.4 msec. Also, large injectors will idle better when sequentially injected, for reasons mentioned in this LINK.
Minimum Injector Opening Time
This parameter can be especially useful for very large injectors that have poor low pulse-width linearity (such as the Bosch 160 lb/hr injectors). This msec value programmed by the user, will prevent the injector pulse-width from fall below the setting, which promotes a much more stable idle speed (idle quality). A good starting value is 1.00 msec. However, unless the injectors are too big or the fuel pressure is too high, most injectors won't reach this setting anyway.
Injector Voltage Offset
All injectors have a voltage off-time/voltage curve, and this needs to be correctly entered into the ECU's software. Sometimes this data can be difficult to find, and contacting the manufacturer is the only way to acquire it. The injector off-time values don't have to be exactly correct. In fact, some aftermarket ECUs just provide generic values. Adjusting the fuel pressure will skew the results somewhat because increasing the fuel pressure does increase the injector off-time values. If the data sheet you find or receive is a short list, you can mathematically find the value in between any two consecutive data points, by averaging.
Example - The data sheet gives you the values for 8 & 10 volts, but you want to find the value for 9 volts: 1.669 (8V) + 1.057 (10V) ÷ 2 = 1.363 (9V).
If your injector data sheet only provides values up to 15 volts, divide that value by 7, and use that subtraction factor for the last six cells. (LINK)
• Another aspect of proper voltage is the alternator. Ensure the alternator can maintain the battery charge at idle. This is a big problem with older alternator designs, even if it's a high amp alternator (and they output a lot of electrical noise). However, modern design alternators are capable of producing most of their power (amps) at idle speeds. These modern designs simply have larger stators, more windings, better rectifiers, etc for greater idle speed output. Ford owners can retrofit a Ford 3G alternator (LINK). GM owners can retrofit a CS-144 alternator (CS-130 for high RPM racing use). I believe Mopar owners can retrofit a certain model Denso alternator.
Alpha-N Idle Fuel
Alpha-N Idle Fuel ("Combo" Load Sensing in Engine Parameters) is a fuel injection strategy, based on TPS Position & RPM. It's for serious race engines with radical camshafts that can't maintain a steady kPa value because it fluctuates too much. Alpha-N Idle Fuel still has the benefits of O2 compensation, however, it can't sense load because it doesn't use the MAP sensor at idle. In Alpha-N mode, most ECUs use the MAP sensor as a Barometric sensor. Alpha-N Idle Fuel should only be used as a last resort. Adding idle resolution to the kPa (Y) axis usually resolves issues with a radical camshaft. Of course, forced-induction applications must use speed-density mode (MAP sensor), since they need to measure load points under boost.
• I once helped a user with their "Alpha-N Idle Fuel" tune. We programmed the Max Alpha-N TPS parameter (TPS axis) at 3%, and the Max Alpha-N RPM (RPM axis) at 1200 RPM. The Fuel Flow (lb/hr) table ranged from 8.5 to 9.0 lb/hr. (Alpha-N was only necessary at actual idle.) The default Alpha-N Idle Fuel table didn't have realistic TPS & RPM values, so program it to your specific application.
Target Idle Speed RPM
Increasing the idle RPM provides a smoother idle. This doesn't mean your engine has to idle at 1000 RPM, however, don't expect a race engine with a radical camshaft to idle at 700 RPM. Generally, the bigger the camshaft the more idle RPM it needs. Most mild performance engines should idle well at 700-800 RPM and most potent street performance engines should idle well at 800-900 RPM. Serious race engines with radical camshafts will need to idle at 900-1000+ RPM, due to the camshaft's tight LSA which causes a high overlap period (not efficient at idle & low RPM). Also, ensure the Target Idle Speed RPM scale is properly programmed. If the hot engine idles in between two temperature cells on the Target Idle Speed scale, set the temperature cell before & after the target idle, to the same RPM; so the ECU doesn't vary the idle speed.
Target Air/Fuel Ratio
Modern cylinder heads with efficient combustion chambers will idle leaner at 14.7-15.2 AFR and require less 20°-22° idle Timing (LINK) with moderate performance camshafts. These newer generation efficient combustion chambers require a lot less overall AFR & Timing. Most older traditional high performance engines will idle well with a target air/fuel ratio between 13.8-14.2 (depending on camshaft specs). This surprised me, and I wasn't comfortable with it at first, because I thought the idle should be leaner at a stoichiometric 14.7:1 AFR. However, when I tried it, my engine responded so favorably, especially when I shifted it in gear. This became one of the three most significant aspects of my idle quality improvement (the other two being timing advance & Fuel Table tuning). This isn't as detrimental to fuel economy as one might think, because at idle, there are less injection events (engine cycles) over time, than at higher RPM. Sequential fuel injection MPFI engines can idle lean at 14.7:1 AFR, even with a street performance camshaft in Closed Loop. Although this requires a relatively wider lobe separation angle such as 114° (LINK - scroll to end). I've found this lean idle AFR is more prevalent with high CFM airflow/port velocity cylinder heads and properly angled fuel injectors (less X-Tau fuel wall wetting - LINK/LINK). Remember to also check the idle in gear, and allow the engine to idle for at least a minute with each change. (LINK)
RPM & kPa Axis Configuration
When an engine is idling, there's a 'target idle cell' on the Fuel & Timing Tables. It's important to identify this single cell, in order to properly configure the RPM (X) axis & kPa (Y) axis. Ideally, the target idle cell should be in the center of the RPM & kPa range the engine idles in. Some engines exhibit better idle stability than others, as seen on the Fuel & Timing Tables. The goal is to configure the idle area so the idle has equal range above & below the target value. Fuel & Timing Tables should have three RPM columns and three kPa rows; one column/row above & below the target column/row. The values programmed above & below the target, depend on how the engine idles and the resolution of the Fuel & Timing Tables (e.g. 16x16 vs. 31x31). Typically, the RPM axis (idle area) has increments of 100-150 RPM, and the kPa axis (idle area) has increments of 2-8 kPa. Adding idle resolution to the kPa (Y) axis can resolve issues with a radical camshaft and/or a forced induction application (with naturally less resolution in the off boost regions of the table). Remember to check the idle in gear, to verify the kPa axis configuration above idle, is acceptable. (LINK)
Base Fuel Table
Sniper/Avenger/Terminator/Terminator X/HP/Dominator EFI users, disregard the following Commander 950 EFI references.
Most people I help, don't know how to tune the idle area of the Fuel Table especially the Commander 950 EFI. It has a big impact on the idle stability. The Base Fuel Table should not be totally flat (except in the Fuel Graph); meaning you can't have the same numbers in the idle area. Unlike the Base Timing Table & Target A/F Ratio Table, which should be flat in the idle area. Below are sample Fuel Table idle tuning scenarios for the Commander 950 EFI. The Fuel Table values are a pulse-width, as opposed to the Sniper/Avenger/Terminator/Terminator X/HP/Dominator Base Fuel Table, which is in pounds-per-hour (LBS/HR). This means the Commander 950 Fuel Graph looks like the engine's torque curve (LINK).
The Holley Sniper/Avenger/Terminator/Terminator X/HP/Dominator EFI LB/HR Fuel Graph looks like the engine's horsepower curve.
The Holley Sniper/Avenger/Terminator/Terminator X/HP/Dominator EFI VE % Fuel Graph looks like the engine's torque curve.
The bold numbers indicate idling with no load (13) & idling in gear and/or accessories on (15). The surrounding cells direct the engine idle back to the target idle cell (center). Study the diagonal pattern of the idle numbers; that's the secret to good Commander 950 Fuel Table idle tuning. Notice how the values increase with higher load & less RPM, and decrease with lower load & more RPM. Example (Commander 950 EFI):
MAP
62...16...15...14
56...15...14...13
50...14...13...12
44...13...12...11
.....700..800..900 RPM
The Fuel Table example above is a good one, however, it illustrates the idle segment of a Commander 950 Fuel Table with large injectors. On Commander 950 Fuel Tables, smaller numbers mean larger injectors, and larger numbers mean smaller injectors. Therefore, if your idle values (numbers) are larger than what's illustrated above (typical injector sizing), then the number pattern should change in increments of two or maybe even three. Example (Commander 950 EFI):
MAP
62...31...29...27
56...29...27...25
50...27...25...23
44...25...23...21
.....700..800..900 RPM
Since the new Avenger/Terminator/HP/Dominator ECUs self-tune, why does the idle area of the Base Fuel Table need to be adjusted? Because the Learn function can only self-tune to the Target Air/Fuel Ratio Table in a floating 3x3 cell (9 block) pattern; and it does so very well. When the Learn Table self-tunes, it's adjusting the entire idle area the same amount; just like it's supposed to. In other words, the Base Fuel Table is responsible for idle quality, and the self-tuning is responsible for WBO2 compensation. So the idle area of the Base Fuel Table needs to be blended smooth (using the Fuel Graph) to promote a smooth idle, for the same aforementioned reasons. When Holley engineers create the base calibrations, it's impossible to know exactly where anyone's engine will idle on the Base Fuel Table. The engine has to be idling to tune the idle. Therefore, the base calibrations must gradually increase the lb/hr values (MAP & RPM) for the Learning to self-tune. The Avenger/Terminator/HP/Dominator EFI Base Fuel Tables use "lbs/hr" unit of measure, so the number incrementation won't be as equally spread as the C950. The point is to manipulate the engine to idle well, by having a smooth Base Fuel Table.
• Ensure the Base Fuel Table is smooth by viewing & blending the Fuel Graph. It's very important to have a smooth Fuel Graph.
One aspect of viewing the Fuel Graph: It's better to zoom in, by highlighting segments of the Base Fuel Table (left click & drag), and click "Graph".
This method offers much greater detail. Looking at the entire "Fuel Graph" will almost always look smooth, because it's not as magnified.
TIP: When the Fuel Graph is smooth, click "Conversion" (VE% Conversion mode) and continue smoothing the general contour of the VE Fuel Graph.
• If you'd like to manually tune the Base Fuel Table (even while the engine is running), read below:
Left click & drag to select a group of cells, then use the CTRL & Arrow keys (▲►▼◄) to change the highlighted cell values.
The ▲ & ▼ arrow keys adjust the Base Fuel Table slowly (one tenth at a time). The ◄ & ► arrow keys adjust it rapidly.
Or you can left click & drag a group of highlighted cells, and right click "Offset Selected" to adjust the entire cell group.
• When the engine is tuned & running well, you should decrease the Closed Loop and Learned Compensation Limits % to lock in a good tune.
I decreased my Learned Compensation Limits to 2% in the idle area (10% elsewhere). My Closed Loop Compensation Limits are 50% or less.
When the Learn Table values stop making significant changes, the ECU is finished self-tuning. (LINK - Read this Learn Table thread, especially posts # 2, # 6 & # 11.)
http://forums.holley.com/showthread....2523#post62523 (Holley EFI Tuning Tips & Information)
https://www.youtube.com/watch?v=y17MClF7SYA (Base Fuel Table/Fuel Graph Tuning - Part 1)
https://www.youtube.com/watch?v=aRn3A5_ecpo (Base Fuel Table/Fuel Graph Tuning - Part 2)
Closed Loop/Learn Compensation ±
ECUs without Learning capability will have a Closed Loop Compensation Limit of around ±25%, and must be tuned so the ECU is subtracting about 5% from the Fuel Table. With a limit of only ±25%, the initial tuning procedure will most likely need to be repeated each time the tuning is applied to the Fuel Table. You won't notice the ECU subtracting fuel, but you can notice it adding fuel. For initial tuning purposes, allow the maximum value in the idle area, due to coolant & air temperature modifiers. ECUs with Learning capability will have a virtually infinite Closed Loop Compensation Limit; as much as ±999%. The reason why, is so the ECU doesn't need to repeat the entire modification to the Base Fuel Table (if the O2 Compensation was limited), every time it returns to idle or any other area for that matter. The Learn Table modifies the Base Fuel Table by applying its Learned amount to the Base Fuel Table values.
• In some stubborn cases, a better idle may be attained by limiting the amount of Closed Loop Compensation or Learning, added or subtracted from the idle area. Also, large duration (race) camshafts will exhibit a fluctuating AFR/false lean condition at idle & low RPM, due to their significant amount of overlap, and/or a WBO2 sensor near the end of an open exhaust pipe. To rectify this, enter Closed Loop Parameters and set the "Enable RPM to Enter Closed Loop" high enough to ignore this condition. You'll then need to manually tune the idle area in Open Loop mode.
• Also, the Advanced Control (1-5) sets how fast the Closed Loop control operates. 1 is the slowest and 5 is the fastest. (The Avenger & Terminator hand-held controller calls this the "Closed Loop Speed".) This depends heavily on where the WBO2 sensor is located in the exhaust system. The further away the WBO2 sensor is (away from the engine), the lower the number should be. If Advanced Control 4 or 5 is selected, one must ensure the ECU isn't oscillating the Closed Loop operation. Viewing a datalog is helpful. I experienced a condition where the actual AFR often "lagged" momentarily, behind the Target AFR. I fixed it by changing the Closed Loop Advanced Control to 5. My WBO2 sensors are located in full-length header collectors. Sometimes it's best to start at a lower value, especially with a fresh base calibration.
• When the engine is tuned & running well, you should decrease the Closed Loop and Learned Compensation Limits % to lock in a good tune. (LINK) I decreased my Learned Compensation Limits to 2% in the idle area (10% elsewhere). My Closed Loop Compensation Limits are 50% or less. When the Learn Table values stop making significant changes, the ECU is finished self-tuning.
Ignition Timing Advance
First, ensure the ignition timing is synchronized (LINK). The Base Timing Table must be flat in the idle area, meaning it's the same value in the entire idle area (especially if using Idle Spark Control). Modern cylinder heads with efficient combustion chambers will idle leaner at 14.7-15.2 AFR and require less 20°-22° idle Timing (LINK) with moderate performance camshafts. These newer generation efficient combustion chambers require a lot less overall AFR & Timing. Most street performance engines will idle well with 15°-25° of timing advance. (Stock cam - 20°, performance cam - 25°, radical cam - 30°). The exact amount depends heavily on the camshaft specifications. Generally, tighter LSA - lobe separation angles (overlap) and larger lobe duration figures, require more timing advance at idle. 106°-108° is considered a tight LSA (idle quality suffers with less idle vacuum), 108°-110° is moderate, 110°-112° is moderately wide, and 112°-114° is wide (idle quality improves with more idle vacuum). One must pay close attention to how much timing advance is used at idle. Resist the urge to use too much; I've made this mistake in the past. Advancing the timing, offers better fuel efficiency and raises the idle speed, however, excessive timing creates an unstable idle speed due to the engine having too much torque at idle (Idle Spark control becomes ineffective). Retarded timing lowers the idle speed, decreases engine torque and increases the coolant temperature. Excessively retarded timing also causes the exhaust headers to glow red hot. Remember to check the idle in gear, to verify the amount used is also acceptable. (LINK)
Idle Spark Control Tuning
The Idle Spark Control basically helps stabilize the idle speed by manipulating the timing (quickly increasing & decreasing in accordance to RPM). The idle quality must be well tuned before adjusting these two parameters. If the idle is well tuned (fuel & IAC), the Idle Spark PID control can actually help determine the optimum timing advance at idle (LINK & LINK). It may help to datalog various P & D combinations (name the datalog by the two numbers to decipher them), and look for the straightest RPM line. This is because you can't watch the idle RPM on the Data Monitor, since they change too fast and the tachometer usually isn't an accurate enough indicator of idle stability. I've found values of 30-40 (P Term) & 50-60 (D Term) are a good start with Holley EFI systems.
P & D Definitions - Excerpt from Holley EFI manual:
• Proportional Term – The speed at which the ignition timing is varied to maintain target idle.
• Derivative Term – Eliminates the overshoot.
IAC Control Tuning
The PID terms must be fine tuned to each particular engine. Start with all three PID parameters at 10. Tune the Proportional first, the Derivative second, the Integral last, then fine tune the three together. Temporarily disable the Idle Spark Control while tuning the idle PID parameters, and ensure the Fuel Map is well tuned in the idle area. It may help to datalog various PID combinations (name the datalog by the three numbers to decipher them), and look for the straightest RPM line. This is because you can't watch the idle RPM on the Data Monitor, since they change too fast, and the tachometer usually isn't an accurate enough indicator of idle stability. Of course, you don't have to datalog the number combinations that obviously make it idle worse. Typically, slower IAC control promotes better idle stability.
PID Definitions - Excerpt from the Holley EFI manual:
• P Term – (Proportional) Speed/gain of the system when there is a large deviation in the target idle speed. Raising this value increases the speed at which the IAC moves in order to remove target idle speed error. If this value is too high for a specific application, the IAC position will oscillate (be out of control), and cause the engine speed to surge up & down. If the value is too low for a specific application, the IAC will be slow to react to quick changes in idle speed deviation. However, it is much better for this term to be conservatively slow, rather than too fast.
• I Term – (Integral) speed of the system when the engine speed is near the target idle speed. Raising this value increases the speed at which the IAC moves when the engine speed is close to target idle speed. If this value is too high for a specific application, there may be “too much IAC activity” around the target idle speed. If the value is too low for a specific application, the IAC will be slow to react to changes near target idle speed. However, it is much better for this term to be conservatively slow, rather than too fast.
• D Term – (Derivative) Higher derivative terms reduce the tendency of idle speed overshoot. Smaller derivative terms slow down the IAC movement as target idle speed is approached.
http://forums.holley.com/showthread....neral-IAC-Info (General IAC Information - Read "IAC NOTES")
IAC Counts or Position (%)
The throttle blades must be set so the engine is breathing sufficient air on its own (without excessive IAC intervention), for idling & starting. The IAC motor/valve is supposed to regulate the idle airflow to help maintain the idle speed. IAC motors have an IAC Position range of either 0-255 counts or 0%-100% (each 1% is the equivalent of 2.55 counts). The throttle blades (idle speed screw) is often set to position the IAC motor at 8-12 counts or 15%+ at hot idle. I've found this to be too much IAC control when it's closing (toward zero). I prefer to further open the throttle blades to achieve a IAC position of 3 counts or 5% at hot idle. This only allows a minute amount of airflow reduction, which always seems to promote a more steady idle speed and improve starting. Remember to perform another TPS Autoset, whenever you adjust the idle speed screw on the throttle body. In the Idle ICF, the "Target Idle Speed (RPM)" must be programmed to the desired RPM speed at hot idle. If the idle speed screw is unscrewed too far, the engine is inhaling air from an additional source - vacuum leak. Ensure the proper type of Advanced Idle Control is selected in Idle Settings. "Slow" may provide the best idle quality. (LINK)
FYI: The Commander 950 EFI system uses IAC Position Counts, not IAC Position %, so don't try copying the Commander 950 IAC values. IAC motors have an IAC position range of either 0-255 counts or 0%-100% IAC Position (each 1% is the equivalent of 2.55 counts).
Injector End Angle
I also spent some time tuning the injector end angle timing. ECUs have different end angle software parameters, so there's an excerpt of how Holley does it below. I like the idea of injecting fuel a little earlier during the intake stroke. The end angle has a diminishing effect as the injector duty cycle reaches 90% (since the injectors are "on" for most of the engine cycle), however, it's nice to tune this for optimum idle quality and low to mid RPM torque. Torque, economy, emissions & idle quality are all effected by the injector timing. The optimum value depends on the engine RPM & load. To notice a difference, the end angle must be adjusted in large increments, such as −45° or −90°. The injection timing can be plotted on paper, if the user knows the injector duty cycle in question, and the intake valve opening (°BTDC) & closing (°ABDC) events. Good technical description from Motec: LINK.
• Excerpt from the Holley EFI manual:
"Injector End Angle - This is the crankshaft angle in degrees when the injectors will finish their injection event. A value of 0° will end the injection event at BDC (Bottom Dead Center) before the compression stroke. A negative value moves the event before BDC, and a positive value moves the event after BDC. There could be some improvements in cylinder to cylinder fuel distribution by tuning this parameter. If modifying, it is best to move this value in a negative direction to start."
• For reference (in Holley EFI software), a 0.0° Injector End Angle value, ends the injection event at BDC (Bottom Dead Center) of the intake stroke, before the compression stroke. This is 540° in the four stroke cycle. A negative value moves the injection event before BDC, and a positive value moves the injection event after BDC. So a −180° Injector End Angle value will end the injection event at TDC (Top Dead Center) of the intake stroke (as the intake valve is opening). Obviously, a −90° Injector End Angle value will end the injection event in the middle of the intake stroke.
FYI: The Holley V4 EFI software/ECU firmware now has much more sophisticated Injector End Angle/Phasing parameters. We discussed it in depth HERE (MPFI engines only).
Injector Pulse-Width
It's important to use the proper size fuel injectors. Injectors that are too large for your application, won't idle well due to low pulse-width operation. Don't decrease fuel pressure in order to increase pulse width times at idle. Decreasing fuel pressure results in less than optimum injector spray patterns. Holley's older EFI documents suggests the pulse-width at hot idle shouldn't be lower than 1.7 msec (which won't be an issue when using the appropriate size injectors), and that it shouldn't fluctuate more than .3 msec. However, the Chief EFI Engineer at Holley stated the new HP & Dominator ECU injector drivers are capable of running the pulse-width at hot idle down to 1.3-1.4 msec. Also, large injectors will idle better when sequentially injected, for reasons mentioned in this LINK.
Minimum Injector Opening Time
This parameter can be especially useful for very large injectors that have poor low pulse-width linearity (such as the Bosch 160 lb/hr injectors). This msec value programmed by the user, will prevent the injector pulse-width from fall below the setting, which promotes a much more stable idle speed (idle quality). A good starting value is 1.00 msec. However, unless the injectors are too big or the fuel pressure is too high, most injectors won't reach this setting anyway.
Injector Voltage Offset
All injectors have a voltage off-time/voltage curve, and this needs to be correctly entered into the ECU's software. Sometimes this data can be difficult to find, and contacting the manufacturer is the only way to acquire it. The injector off-time values don't have to be exactly correct. In fact, some aftermarket ECUs just provide generic values. Adjusting the fuel pressure will skew the results somewhat because increasing the fuel pressure does increase the injector off-time values. If the data sheet you find or receive is a short list, you can mathematically find the value in between any two consecutive data points, by averaging.
Example - The data sheet gives you the values for 8 & 10 volts, but you want to find the value for 9 volts: 1.669 (8V) + 1.057 (10V) ÷ 2 = 1.363 (9V).
If your injector data sheet only provides values up to 15 volts, divide that value by 7, and use that subtraction factor for the last six cells. (LINK)
• Another aspect of proper voltage is the alternator. Ensure the alternator can maintain the battery charge at idle. This is a big problem with older alternator designs, even if it's a high amp alternator (and they output a lot of electrical noise). However, modern design alternators are capable of producing most of their power (amps) at idle speeds. These modern designs simply have larger stators, more windings, better rectifiers, etc for greater idle speed output. Ford owners can retrofit a Ford 3G alternator (LINK). GM owners can retrofit a CS-144 alternator (CS-130 for high RPM racing use). I believe Mopar owners can retrofit a certain model Denso alternator.
Alpha-N Idle Fuel
Alpha-N Idle Fuel ("Combo" Load Sensing in Engine Parameters) is a fuel injection strategy, based on TPS Position & RPM. It's for serious race engines with radical camshafts that can't maintain a steady kPa value because it fluctuates too much. Alpha-N Idle Fuel still has the benefits of O2 compensation, however, it can't sense load because it doesn't use the MAP sensor at idle. In Alpha-N mode, most ECUs use the MAP sensor as a Barometric sensor. Alpha-N Idle Fuel should only be used as a last resort. Adding idle resolution to the kPa (Y) axis usually resolves issues with a radical camshaft. Of course, forced-induction applications must use speed-density mode (MAP sensor), since they need to measure load points under boost.
• I once helped a user with their "Alpha-N Idle Fuel" tune. We programmed the Max Alpha-N TPS parameter (TPS axis) at 3%, and the Max Alpha-N RPM (RPM axis) at 1200 RPM. The Fuel Flow (lb/hr) table ranged from 8.5 to 9.0 lb/hr. (Alpha-N was only necessary at actual idle.) The default Alpha-N Idle Fuel table didn't have realistic TPS & RPM values, so program it to your specific application.
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