Hard Hot Start With Air Cleaner Installed

[copter]

My Avenger MPFI starts great cold & hot without an air filter installed.
I installed an air filter, it starts good cold, but now it's hard starting hot.
If I take the lid off the air cleaner it starts up with no problem. ???

[Danny Cabral]

I installed an air filter, it starts good cold, but now it's hard starting hot.
If I take the lid off the air cleaner it starts up with no problem. ???

1) First, ensure the idle speed screw is adjusted to achieve an IAC Position of about 5% at hot idle.
Remember to perform another TPS Autoset, whenever you adjust the idle speed screw on the throttle body.
Read the hot engine Cranking Fuel lbs/hr "TIP" in post #6 below. Also note Fuel Prime Percent information.
https://forums.holley.com/showthread...894#post219894 (Good Startup Tuning Advice Post)

2) Second, you might need to increase the IAC Parked Position at that engine temperature (Idle ICF). See post #4 below.
Turn the ignition key on, wait for the WBO2 sensor to display AFR, then start the datalogger & engine.
This allows you to determine if the Cranking Fuel and immediate engine AFR is excessively rich or lean.
http://forums.holley.com/showthread....7913#post77913 (Related Cranking/Startup Tuning Post)

3) Third, in the Holley EFI software (LINK), also look at the Coolant Temperature Enrichment %
table and the Air Temperature Enrichment % table (both are in the Fuel ICF - Fuel Modifiers).
The Coolant & Air Temperature Enrichment % tables are active immediately after starting the engine.
http://forums.holley.com/showthread....6649#post66649 (Coolant Temperature Enrichment % Table Tuning)
http://forums.holley.com/showthread....7913#post67913 (Air Temperature Enrichment % Table Tuning)

4) If Learning has finished self-tuning the Base Fuel Table, you can tune the Coolant Temperature Enrichment & A/F Ratio Offset Tables.
Usually, the Coolant Temperature Enrichment % & A/F Ratio Offset tables are too rich in the base calibrations.
In my entire Coolant Temperature Enrichment table, I don't have a value higher than 130%. Everything is 130% (-5°F) to 100% (175°F-220°F).
In my entire A/F Ratio Offset table (also in Fuel Modifiers), I don't have a value lower than −0.5. Everything is −0.5 (-5°F) to zero (70°F-220°F).
I reconfigured my coolant temperature axis from -5°F to 220°F (Sensor Scaling/Warnings in System ICF), for more resolution in a realistic range.
http://forums.holley.com/showthread....ing-Precedence (Additional Enrichment/Modifiers Information)

5) Open the Holley EFI software "Help" Contents ("Help" drop down menu), and read "Step-By-Step Beginner's Tuning".
In Step-By-Step Beginner's Tuning, see the "Idle Fuel vs. Temperature" graphical representation - Figure 8, Section 5.1.
Under 400 RPM (default "Crank-To-Run RPM" parameter), the ECU only uses the Cranking Timing, Cranking Fuel (lb/hr) & IAC Parked Position % tables.
See page 14: http://documents.holley.com/techlibrary_199r11259.pdf (Holley Sniper EFI Help Manual - EFI Software, Tuning & Datalogging)

EFI Software Help Information/Instructions:
‒ On the top Toolbar, click "Help" & "Contents". This opens all Help topics.
‒ When navigating the software, click "Help ?", drag it to any parameter and click again.
..This automatically opens the definitions for that specific parameter.
‒ Tuning information can be read by clicking the F1 key, when you're viewing any screen.
http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual & Diagrams)
http://documents.holley.com/techlibrary_199r10544.pdf (Holley EFI Help/Instructions Overview)
http://forums.holley.com/showthread....ents-Read-This! (Initial Checks & Adjustments - Read This!)

[copter]

Danny, I have the street/strip cam tune programmed now. Do you think if I programmed it for the mild street cam it would help? The car is street driven only with a hydraulic roller cam with a duration of 244° @ .050". I'm thinking leaning it out with the mild street tune may help. What are your thoughts? Thanks.

[Danny Cabral]

Danny, I have the street/strip cam tune programmed now. Do you think if I programmed it for the mild street cam it would help?

Not likely; most of the starting parameters are the same anyway.

I'm thinking leaning it out with the mild street tune may help. What are your thoughts?

First, let's cover the basics:
http://forums.holley.com/showthread....ents-Read-This! (Initial Checks & Adjustments - Read Steps #1-#6!)

The Learn Table (Fuel ICF) should be populating the table with numbers. If not, determine why it's not Learning.
Check your Closed Loop/Learn Parameters. "Enable Closed Loop" and "Base Fuel Learn Enabled" are the only parameters that need to be check marked.

Second, ensure the fuel pressure is properly adjusted and the "Actual System Pressure" is accurately entered in Engine Parameters.
With TBI, the Actual System Pressure is measured anytime engine is running (no vacuum reference hose), or key-on/engine-off pump running.
With MPFI, the Actual System Pressure is measured with the vacuum reference hose temporarily disconnected, or key-on/engine-off pump running.

Third, how does it fail to start? Just keeps cranking or initially fires, but immediately stalls? See table below:
Turn the ignition key on, wait for the WBO2 sensor to display AFR, then start the datalogger & engine.
This allows you to determine if the Cranking Fuel and immediate engine AFR is excessively rich or lean.

Originally Posted by Danny Cabral • Starting Issues - initially starts, but stalls immediately after: When it stalls, how does it die? Quick & clean (quick stall) = too lean* Spit & sputter (slow stall) = too rich Tune the After Start Enrichment accordingly. If engine stalls several seconds after starting, tune the Coolant Temperature Enrichment Table or After Start Decay Rate. May also be caused by using the wrong base calibration for the MAP sensor in use (Base Fuel Table excessively lean or rich). * If the tune is excessively rich, it can stall immediately after startup, due to flooding (extinguishing) the spark. • Notes - starts & runs, but potentially could be better: If it starts worse, with the throttle cracked open, it's too lean. If it starts better, with the throttle cracked open, it's too rich (or throttle blades were closed too far.) The Cranking Fuel (lb/hr) & IAC Parked Position % are the "cranking air/fuel ratio". Tune these tables. Adjust the idle speed screw on throttle body, to achieve an IAC Position of about 5% at hot idle. Some engines start better with more timing while cranking (Cranking Timing in Ignition Parameters). Ensure the ignition timing is synchronized: http://forums.holley.com/showthread....ing-Holley-EFI Sequentially injected engines will always crank slightly longer for the ECU to receive the cam sync signal. The new Quick Start "Fuel Prime Percent" feature works very well, but be careful; too much % will start fine cold, but not hot. • You can only tune the Startup Enrichment parameters after the Learning has self-tuned the Base Fuel Table and if the Coolant Temperature Enrichment & A/F Ratio Offset tables are acceptable. This is because the aforementioned parameters & tables are modifiers of the Base Fuel Table. Exception: Cranking Fuel (lb/hr), Cranking Timing & IAC Parked Position %, because they function independently under 400 RPM (or whatever your "Crank To Run RPM" is). FYI: The "Crank To Run RPM" parameter (in Ignition Parameters) is not your actual cranking RPM when starting the engine.

[copter]

The fuel pressure is set at 42 psi. When I start it hot, it fires for a split second, then just turns over until I feather the throttle and it starts. It does not stall after it starts.

[Danny Cabral]

When I start it hot, it fires for a split second, then just turns over until I feather the throttle and it starts.

Then it's too rich. Try decreasing the Cranking Fuel (Startup Enrichment - Fuel ICF) and/or increasing the IAC Parked Position (Idle ICF) at that engine temperature. However, this can only be performed after the Learning has finished self-tuning the idle area of the Fuel Table, which it probably has by now.

TIP: For most engines, the amount of lb/hr IDLE fuel (Base Fuel Table, +/− Learn Table) should also be a good starting point for the HOT Cranking Fuel cells (hot restart).
And maybe even slightly less, if the Fuel Prime Percent is high, such as 200% or higher. (See post #15 below for additional Fuel Prime Percent information & suggestions.)
The hot lb/hr may not apply to non-vacuum referenced fuel pressure regulator applications due to their higher fuel pressure at idle, cruise, light acceleration & deceleration.
As a result, their lb/hr idle fuel values (Base Fuel Table) are lower in comparison, and since there's no engine vacuum when cranking, the correlation isn't the same.
Exception: TBI fuel pressure regulators (with injectors above throttle blades) aren't vacuum referenced because the injectors aren't subjected to intake manifold vacuum.
https://www.vaporworx.com/documentat...re-regulators/ (Vacuum Referenced Fuel Pressure Regulators)

NOTE: Disregard the fuel Autoprime reference in the "Help" Contents. That's not for the V2/V3 EFI software/firmware.
Read section 6.2 Fuel Prime in the 199R10632rev5 PDF document - "V2 Software Update Overview":

Originally Posted by Holley V2 Software Update Overview 6.2 Fuel Prime There is a new fuel priming “Quick Start” feature available for every type of system. For MPFI applications, the system will inject a single pulse of fuel, after the first crank pulse is detected. This will only re-occur after an engine starts. In other words, if you try to start an engine and it doesn’t successfully fire, it will not keep adding this fuel - only the first time it sees a crank tooth, for that run event. For TBI applications, the system will inject a single pulse of fuel when the key turns on to wet the intake manifold. This will only re-occur, after an engine has started. If you cycle the ignition key multiple times, it will only perform the first prime. This feature must be enabled, by selecting the "Enable Fuel Prime" check box located in the System ICF under System Parameters > Engine Parameters > Startup Settings. Once the "Enable Fuel Prime" box is checked, it will show the "Fuel Prime Percent" parameter. The "Fuel Prime Percent" is a multiplier that works off the "Cranking Fuel" Value in the Startup Enrichment table. The pulse width of the single shot of fuel prime fuel is based off the Cranking Fuel value (which is temperature based) and multiplied by the "Fuel Prime Percent". A starting value of 200% is usually a good point for MPFI engines and 50% for TBI applications, with a range of 40%-250% usually being an acceptable range. This can be adjusted as needed.

[copter]

I dropped the Cranking Fuel from 25 to 20, drove it around until it got to 180°, cut it off, and 10 minutes later it fired right up. I'll see what happens in the next few days and let you know if that was the problem. Thanks! Danny, have you ever thought of getting a 1-800 number? LOL!

[Thumper28]

First, ensure the idle speed screw is adjusted to achieve an IAC Position of about 5% at hot idle.

Danny, is the 5% adjustment rule true for throttle bodies that already have a orifice through the butterfly plate? My stock LS1 has roughly a 1/8" bypass hole in the plate already.

[Danny Cabral]

Danny, is the 5% adjustment rule true for throttle bodies that already have a orifice through the butterfly plate? My stock LS1 has roughly a 1/8" bypass hole in the plate already.

Yes. The engine idles with a specific amount of airflow, whether it has a bypass hole or not.

[Sponge]

I dropped the Cranking Fuel from 25 to 20, drove it around until it got to 180°, cut it off, and 10 minutes later it fired right up.
I'll see what happens in the next few days and let you know if that was the problem. Thanks!
Danny, have you ever thought of getting a 800 number? LOL!

I know it's an old topic, but 20 lbs/hr Cranking Fuel hot seems like a lot, because I've got only 4.5 on mine. Was engine hot, and it fires right up?

[Danny Cabral]

I know it's an old topic, but 20 lbs/hr Cranking Fuel hot seems like a lot, because I've got only 4.5 on mine.

4.5 lbs/hr Cranking Fuel (hot) may be enough for smaller engines, but it's not enough on larger engines. My 508" BBF Cranking Fuel is 9 lbs/hr at 180°F & higher. Also, ensure the "Actual System Pressure" parameter is correctly programmed in Engine Parameters. If it's not, the lb/hr values will be inaccurate (throughout the EFI software).

[Sponge]

20 lbs/hr from -20°F − 80°F
18 lbs/hr at 100°F
16 lbs/hr at 120°F
7.3 lbs/hr at 140°F
5.7 lbs/hr at 160°F
4.5 lbs/hr at 180°F − 260°F

So I'm asking if my "After Start Enrichment" is not too high: 114 from 140°F till 260°F. If I understand those figures well; the Decay Rate is the number of seconds it takes to "spray" the additional percentage in the "After Start Enrichment"? For example, 114% means it takes xx seconds to spray 14% of what? Cranking Fuel?

[Danny Cabral]

If I understand those figures well; the Decay Rate is the number of seconds it takes to "spray" the additional percentage in the "After Start Enrichment"?

EFI Software Help Information/Instructions:
‒ On the top Toolbar, click "Help" & "Contents". This opens all Help topics.
‒ When navigating the software, click "Help ?", drag it to any parameter and click again.
..This automatically opens the definitions for that specific parameter.
‒ Tuning information can be read by clicking the F1 key, when you're viewing any screen.
http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual & Diagrams)
http://documents.holley.com/techlibrary_199r10544.pdf (Holley EFI Help/Instructions Overview)
http://forums.holley.com/showthread....ents-Read-This! (Initial Checks & Adjustments - Read This!)

In the "Help" Contents of the EFI software (Step-By-Step Beginner's Tuning), look at the "Idle Fuel vs. Temperature" graphical representation - Figure 8, Section 5.1.
Under 400 RPM (the "Crank To Run RPM"), the ECU only looks at the Cranking Fuel (lb/hr) Table, the Cranking Timing value, and the IAC Parked Position %.

Cranking Fuel & After Start Enrichment are not the same thing. Cranking Fuel only happens during cranking. When the engine starts, the After Start Enrichment is injected for a brief period of time (After Start Enrichment Time - Decay Rate). The After Start Enrichment fuel is a modifier (%) of the Base Fuel Table, based on coolant temperature. The After Start Decay Rate (linear decay to zero) is the time duration of the After Start Enrichment in seconds.

[andrewb70]

I'm trying to optimize my hot starting as well. To me, it seems that the engine should fire up very clean & crisp when hot, and mine just doesn't. With respect to Cranking Fuel, wouldn't this number be similar to the fuel flow rate at idle? Andrew

[Danny Cabral]

With respect to Cranking Fuel, wouldn't this number be similar to the fuel flow rate at idle?

On most engines, it is a good hot starting point (see post #6). Some engines like more Cranking Fuel. Try it both ways and see which amount your engine likes. Also, some engines don't tolerate a lot of "Fuel Prime Percent" on hot restarts. Keep in mind, the Fuel Prime Percent is based off of your Cranking Fuel values. So if your Cranking Fuel values aren't well tuned, the Fuel Prime Percent will be wrong too. Most MPFI small block engines should start good at 150%. Most MPFI big block engines should start good at 200%. TBI engines will require less, maybe half the aforementioned percentages. (100% is the neutral factor that doesn't add or subtract Fuel Prime.)