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Thread: Dies On Deceleration

  1. #1

    Default Dies On Deceleration

    OK, idles well at 900 RPM now. I'm going to try to get it down a little lower. However, I went out for a drive. Drives well except for two things:

    1. The car continually dies on deceleration. On deceleration, if I keep it in gear, it will obviously continue to run. However, once I push in the clutch, the car will return to idle, then drop lower than the programmed idle, then die. If I blip the throttle to keep it from dying, I notice the RPM increase to about 1300, stays there for a second or two, slowly drops to about 1000, then it drops again and tries to die. If I blip the throttle again, it will do the same. Eventually, I can get it back to idle, but it takes a few blips of the throttle.

    2. Hard starts. Cold or hot. I hear the fuel pump 5 second prime with key-on. It takes sometimes 15-20 seconds to start. Pumping the throttle has no effect. Crank timing is 15°. Timing is synced & verified with a timing light. Fuel pressure is verified at 43 psi with engine running, vacuum disconnected - then vacuum reconnected. Engine is a 408 ci Windsor. Cam is 230°/236° @ .050" duration, .600" lift, 112° lobe separation. Any specific changes recommended to make starts easier?

  2. #2
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    Quote Originally Posted by Texasdoc View Post
    1. The car continually dies on deceleration. On deceleration, if I keep it in gear, it will obviously continue to run. However, once I push in the clutch, the car will return to idle, then drop lower than the programmed idle, then die. If I blip the throttle to keep it from dying, I notice the RPM increase to about 1300, stays there for a second or two, slowly drops to about 1000, then it drops again and tries to die. If I blip the throttle again, it will do the same. Eventually, I can get it back to idle, but it takes a few blips of the throttle.
    This is usually caused by a Base Fuel Table that's too lean (especially with a manual transmission).
    Also, adjust the idle speed screw on throttle body, to achieve an IAC Position of about 2% at hot idle.
    Remember to perform another TPS AutoSet, whenever you adjust the idle speed screw on the throttle body.

    On an opposite note, Acceleration Enrichment can't be tuned until the Base Fuel Table is well tuned.
    If you have a momentary lean spike, on light throttle acceleration, check
    your AE vs TPS/MAP RoC Blanking values (in Fuel Modifiers/Fuel Control):
    If they're 15 & 7, those are the old values from the V1 firmware.
    Change the AE vs TPS RoC Blanking value to 4-6.
    Change the AE vs MAP RoC Blanking value to 5-7.
    Some users reported the need for an even lower TPS RoC Blanking value.

    2. Hard starts. Cold or hot. I hear the fuel pump 5 second prime with key-on. It takes sometimes 15-20 seconds to start. Pumping the throttle has no effect. Crank timing is 15°. Timing is synced & verified with a timing light. Fuel pressure is verified at 43 psi with engine running, vacuum disconnected - then vacuum reconnected. Engine is a 408 ci Windsor. Cam is 230°/236° @ .050" duration, .600" lift, 112° lobe separation. Any specific changes recommended to make starts easier?
    http://forums.holley.com/showthread....6254#post36254 (Good Starting Advice Thread)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

    Default

    OK, so here's my Learn Table. I'm thinking I should merge this with my Base Fuel Table, then increase the base table to 20 around the idle area. I think it's adding fuel since I have a 408, and the base calibration is for a 350. Should I do this or just wait for it to Learn itself?

    Name:  LearnTable.jpg
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  4. #4

    Default

    I increased my Cranking Timing to 20° to see if that helps. Here is my Cranking Fuel Table. Should I increase this? By what amount?

    Name:  Cranking Fuel.jpg
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Size:  70.8 KB

  5. #5
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    Quote Originally Posted by Texasdoc View Post
    Should I do this or just wait for it to Learn itself?
    I would wait until the Learn Table finishes self-tuning the Base Fuel Table. Then Transfer Learning To Base and smooth the 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.

    Quote Originally Posted by Texasdoc View Post
    I increased my Cranking Timing to 20° to see if that helps.
    15° Cranking Timing is fine. You can leave that alone.

    Here is my Cranking Fuel Table. Should I increase this? By what amount?
    No one else can answer that. Only you can tune your engine. Try increasing all cells by 5 lbs/hr.
    All the other starting parameters can't be tuned until the Base Fuel Table is well tuned.
    http://forums.holley.com/showthread....6254#post36254 (Good Starting Advice Thread)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  6. #6

    Default

    Quote Originally Posted by Danny Cabral View Post
    This is usually caused by a Base Fuel Table that's too lean (especially with a manual transmission).
    Also, adjust the idle speed screw on throttle body, to achieve an IAC Position of about 2% at hot idle.
    Remember to perform another TPS AutoSet, whenever you adjust the idle speed screw on the throttle body.
    Already done. TPS at zero (after reset). IAC fluctuates from 2-5% at idle.

    Quote Originally Posted by Danny Cabral View Post
    On an opposite note, Acceleration Enrichment can't be tuned until the Base Fuel Table is well tuned.
    If you have a momentary lean spike, on light throttle acceleration, check
    your AE vs TPS/MAP RoC Blanking values (in Fuel Modifiers/Fuel Control):
    If they're 15 & 7, those are the old values from the V1 firmware.
    Change the AE vs TPS RoC Blanking value to 4-6.
    Change the AE vs MAP RoC Blanking value to 5-7.
    Some users reported the need for an even lower TPS RoC Blanking value.
    Both are at 7. Will change AE vs MAP RoC to 4.

    I initially had the default settings:
    IAC Hold Position - 30%
    Ramp Decay Time - 4.0 sec
    RPM Above Idle to Start Ramp - 1500 RPM
    RPM Above Idle to Re-enable Idle Control - 50 RPM

    I left this alone for a while and drove around, blipping the throttle when it would almost die. Whenever it would fall too low, but seem like it wouldn't die, I let it figure it out. Eventually, it got where it would not die - it learned. However, whenever I would blip the throttle, the RPM would increase to about 1600, hold there for a second, then slowly decrease back to idle. This was really annoying when trying to creep thru a parking lot or going slowly thru the neighborhood. Sounded like I was over-revving the engine just to be an annoyance to others - trying to show off.

    So, I tried to set the IAC to these settings recommended in another thread:
    IAC Type - Stepper
    IAC Hold Position - 20%
    Ramp Decay Time - 2.0 sec
    RPM Above Idle to Start Ramp - 1000 RPM
    RPM Above idle to Re-enable Idle Control - 50-200 RPM

    However, that made the die-on-deceleration problem reappear. It doesn't hold the high idle, but continues to die now, despite an hour long drive today in attempt to get it to relearn. I'll try some in-between settings: IAC Hold 30%, Decay 3 sec.
    Last edited by Texasdoc; 10-28-2014 at 08:06 PM.

  7. #7
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    Quote Originally Posted by Texasdoc View Post
    However, that made the die-on-deceleration problem reappear. It doesn't hold the high idle, but continues to die now, despite an hour long drive today in attempt to get it to relearn.
    I would datalog this occurrence. Scrutinize the RPM, AFR & Timing (maybe it's not the IAC).
    Also, overlay the datalog, and watch where this happens on the Fuel & Timing Tables.
    First tune the Fuel Table with the "Decel Fuel Cutoff" disabled (if it isn't already). It should only be used after the engine is tuned.

    Also, 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.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  8. #8

    Default

    Here are a couple of datalogs of the occurrence:
    Datalog1.jpg

    Datalog3.jpg

    Datalog4.jpg

    What appears to me, is that as the IAC ramps down from 30%, the RPM falls below the target RPM. This causes the timing to fall to around 20°. The lowest programmed timing cell on my timing table is 25°. This then causes the IAC to open back up, which raises the RPM, restores the timing, and then the IAC starts dropping again.

    Here is my timing table: TimingTable.jpg

    All the spark modifiers are at zero.

    See next post for overlay data.

    I have confirmed my timing sync is correct & stable thru the RPM range when static timing is enabled.
    I set the fuel pressure at 43 with pump on, engine off - then connected the manifold reference.
    I have the Ford TFI ignition module, not the MSD module that came with the distributor.
    Base Fuel Table Graph is smooth.
    Decel Fuel Cutoff is disabled.

    It is better with the current IAC settings of 30% & 3 second ramp, than it was with 25% & 2.5 seconds, but the hanging idle is a little worse.
    There was no low RPM/die on deceleration when the IAC was 30%, 4 seconds, but it caused a hanging idle.
    Last edited by Texasdoc; 10-31-2014 at 05:56 PM.

  9. #9

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    Figured out the overlay.
    Datalog with Overlay of lowest timing point: Datalog1Overlay.jpg

    Base Fuel Table with overlay: Base%20Fuel.jpg
    Learn Fuel Table with overlay: Learned%20Fuel.jpg
    Timing Table with overlay: Timing%20Overlay.jpg

    So, when my timing is datalogged at around 20°, the ECU (per the Overlay) is commanding 25°-27° degrees.

    When the RPM is at its lowest (500 RPM at around 30 seconds into the datalog), the commanded timing per the datalog is 30°.
    The overlay on the Timing Table says it should be 25°. LowIdleTiming.jpg

    Any ideas on why the datalog and the overlayed tables don't match? Any other ideas?
    Last edited by Texasdoc; 10-31-2014 at 05:55 PM.

  10. #10
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    Quote Originally Posted by Texasdoc View Post
    What appears to me, is that as the IAC ramps down from 30%, the RPM falls below the target RPM. This causes the timing to fall to around 20°. The lowest programmed timing cell on my timing table is 25°.
    If the idle drops below 400 RPM (typical "Crank To Run RPM" in Ignition Parameters), it momentarily reverts back to the Cranking Timing (usually 15°), Cranking Fuel (Startup Enrichment), and the IAC Parked Position %. Does the idle ever drop this low?

    This then causes the IAC to open back up, which raises the RPM, restores the timing, and then the IAC starts dropping again.
    A poor running engine will idle at much higher kPa, creating a rich or lean condition (depending on the base calibration's Base Fuel Table) due to idling high on the Base Fuel Table. In other words, your engine's idle should never drop far enough to reach 95 kPa.

    It is better with the current IAC settings of 30% & 3 second ramp, than it was with 25% & 2.5 seconds, but the hanging idle is a little worse. There was no low RPM/die on deceleration when the IAC was 30%, 4 seconds, but it caused a hanging idle.
    When everything is properly tuned, the difference of 25-30% IAC Hold Position, or 2.5-3 seconds Ramp Decay Time is insignificant (especially won't cause stalling). What does the engine idle at, and what's the Target Idle Speed RPM? What size camshaft is this?

    Already done. TPS at zero (after reset). IAC fluctuates from 2-5% at idle.
    Adjust the idle speed screw so the IAC Position is closer to 1-2%, rather than 5% (at hot idle).
    Remember to perform another TPS AutoSet, whenever you adjust the idle speed screw on the throttle body.

    Learn Fuel Table with overlay: Learned%20Fuel.jpg
    I see some full lean, and some rich spikes in your datalogs. Again, what size camshaft is this? The engine started stalling because the AFR got too rich.
    Also, judging by your Learn Table, you started with a base calibration that was too lean (which is the worst case scenario with a manual transmission).

    So, when my timing is datalogged at around 20°, the ECU (per the Overlay) is commanding 25°-27° degrees.
    That was the Idle Spark control doing its job to stabilize the idle speed, by decreasing the ignition timing. Unless there was an active -7° (±) timing modifier somewhere? Read below.

    When the RPM is at its lowest (500 RPM at around 30 seconds into the datalog), the commanded timing per the datalog is 30°.
    The overlay on the Timing Table says it should be 25°. LowIdleTiming.jpg
    That was the Idle Spark control doing its job to stabilize the idle speed, by increasing the ignition timing.

    Ensure there aren't any active 'timing modifiers' at this point (e.g. Timing vs Coolant Temperature, Timing vs Manifold Air Temperature, Knock Retard, etc.). Also, ensure you don't have any erroneously programmed "Warning Enabled Timing Offset" parameters in the "Sensor Scaling/Warnings" (System ICF) or in the custom Inputs (Inputs/Outputs ICF). If you're not sure, use the EFI software "Enable Static Timing Set" (in the "Sync With ECU" drop down menu - top Toolbar).
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

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