Skipping/sputtering under boost.

M

mommasGN

Active Member
Joined
May 22, 2013
hello all, i have a new issue ive been fighting since the last time i ran at the track about a month ago. That day, on the way to the track, the car would spit and sputter as soon as i got to about 10 psi. Once at the track however....it ran beautiful. ran my fastest 1/8 mile time ever and the engine didnt miss a beat. Then, on the way back home doing a few highway pulls it was backfiring/skipping under boost again. other wise driving like a champ.

Since it been so nice lately ive been driving the car more often on the daily. I am having the same issue. Car drives amazing until it gets into boost,about 10 psi or so. Then it skips like crazy. Sometimes feels like random skips, sometimes it feels like its on a 2-step. Sometimes it backfires and engine looses total power until you take your foot off.....then it returns to idle and you can continue driving like normal.

I have changed plugs twice with the same ngks i always use and tried a set of ac delco. disconnected 2 step. swapped coil packs with a spare i had that never had an issue before. FP rising 1:1 with boost (i have transducer for powerlogger). TPS voltage smooth the whole range of travel. It happens after MAF reaches 255 so i have no reason to believe its that. Alt voltage and all grounds good.

I have not replaced wires yet, they appear fine but that doesnt mean anything.

I am pretty sure my sig is up to date.

any help is much appreciated.

Nick
 
A bad ignition module will sometimes act up like you're describing. As it heats up the problem will appear and after it cools down some, act normally again.
 
Log it so we can see what everything looks like when it happens . I had a problem with the car stumbling and caught it in a log where power to the ECU would drop out for a split second and all reading went to zero then came back . It turned out to be a bad connection on the main harness at the ECU . I replaced both connectors with Caspers pig tails and all was good .
The point is I never would have found it without the data log .
 
dynoman said:
Log it so we can see what everything looks like when it happens . I had a problem with the car stumbling and caught it in a log where power to the ECU would drop out for a split second and all reading went to zero then came back . It turned out to be a bad connection on the main harness at the ECU . I replaced both connectors with Caspers pig tails and all was good .
The point is I never would have found it without the data log .
Click to expand...
i had free time today so i went out to log some driving and......dead laptop battery. next trip out i will log some.
 
mommasGN said:
hello all, i have a new issue ive been fighting since the last time i ran at the track about a month ago. That day, on the way to the track, the car would spit and sputter as soon as i got to about 10 psi. Once at the track however....it ran beautiful. ran my fastest 1/8 mile time ever and the engine didnt miss a beat. Then, on the way back home doing a few highway pulls it was backfiring/skipping under boost again. other wise driving like a champ.

Since it been so nice lately ive been driving the car more often on the daily. I am having the same issue. Car drives amazing until it gets into boost,about 10 psi or so. Then it skips like crazy. Sometimes feels like random skips, sometimes it feels like its on a 2-step. Sometimes it backfires and engine looses total power until you take your foot off.....then it returns to idle and you can continue driving like normal.

I have changed plugs twice with the same ngks i always use and tried a set of ac delco. disconnected 2 step. swapped coil packs with a spare i had that never had an issue before. FP rising 1:1 with boost (i have transducer for powerlogger). TPS voltage smooth the whole range of travel. It happens after MAF reaches 255 so i have no reason to believe its that. Alt voltage and all grounds good.

I have not replaced wires yet, they appear fine but that doesnt mean anything.

I am pretty sure my sig is up to date.

any help is much appreciated.

Nick
Click to expand...
Bet it’s your ignition module. Mine did the same thing. Acted like it had a 2200 rpm 2 step. Sent mine to Steve V and he tested it. At 2200 it just shut off spark. I replaced mine with a tr6 and haven’t had any issues since.
 
no change with new AC Delco ignition module.(i know brand new they can be junk as well). I have my laptop with me today so i will get some logs
 
Here is a PL file of my drive to work this morning. I just hit record and started driving. I have the boost turned down, and timing turned down just to be safe. I got into it at frames 6140, 7700, and 10500. The first two, it didnt pop/backfire but it still skipped like crazy (almost feels like a 2-step) The third pull, It did the loud pop.

I dont see anything obvious. Doesn't lose bat voltage, I thought maybe crank sensor was losing signal, but i feel like that would show up in the rpm graph. Being that it is skipping is setting the knock sensor crazy.


I have plug wires arriving today to try.
 

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Yes, So do we think whatever is causing the KR is also causing the mis or backfire.....or is the mis/backfire setting off the Knock sensor?

If andengine is losing spark or ignition, so raw fuel is being pushed through the exhaust, what will that show up as on and A/F sensor or narrowband sensor?

Note: Pressure 4 is fuel pressure, Pressure 5 is oil pressure.
 
SCOOBY DOO said:
Frame 6149 shows a shitload of KR with WB at 13.89 and NB at 196.
Click to expand...
You are correct. What does raw fuel read on an A/F sensor or narrowband, on say and engine that is losing ignition causing a misfire? Does it show up as a lean spike or show rich?

Im not 100% convinced its and ignition issue but that is certainly what it feels like.
 

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Don't rule out a stuck or bad injector. I had one once and it made the car run really bad. The easiest way to tell is to wait until the car is cold, then cycle the key to on and let the fuel pump prime the system. Then pull the plugs and use a hose to sniff the spark plug holes. The one that smells like strong fuel is bad.
 
Is it back firing in the exhaust or through the intake? Looking at your screenshot, the wb is very lean.
 
Last edited:
Frames 7768 and 10,623 you had just gotten out of it but it was still registering KR. That seems odd.

Do you have a volt booster installed or something that makes the volts increase to 16v when you're into the throttle?

As Scooby noted, your narrowband is dropping down very low and corresponds with high KR spikes. Maybe it's time to take a look at that sensor? I see you're using an LC-1 WB. When was the last time you changed the WB 02 and did a calibration? There's 'free air' and 'heater'.

*****************************************************************************************************************************************************

3.1 Heater Calibration 1. Remove the sensor from the exhaust, the sensor needs to be in free air for this procedure. 2. Disconnected the sensor from the LC-1’s sensor connector. 3. Switch 12V supply to the LC-1 ON. The LED will flash a two blink sequence with a 2 second pause during this time. Leave the unit powered ON for 20 seconds. 4. Switch the 12V supply off after 20 seconds. 5. Connect the sensor to the LC-1’s sensor interface connector but do not put the sensor in the exhaust. The sensor must be removed from the exhaust and exposed to free air for this calibration. 6. Switch the 12V supply to the LC-1 ON. The LED will first blink steady about 2 times/second: indicating that the sensor is warming up. The LED will then start a faster blinking sequence about 4 times/second indicating a Heater calibration. When the Heater Calibration is done the LED will light up and remain solid. 7. While the sensor is still removed from the exhaust perform a free air calibration.
 
Dan SS2471 said:
Frames 7768 and 10,623 you had just gotten out of it but it was still registering KR. That seems odd.

Do you have a volt booster installed or something that makes the volts increase to 16v when you're into the throttle?

As Scooby noted, your narrowband is dropping down very low and corresponds with high KR spikes. Maybe it's time to take a look at that sensor? I see you're using an LC-1 WB. When was the last time you changed the WB 02 and did a calibration? There's 'free air' and 'heater'.

*****************************************************************************************************************************************************

3.1 Heater Calibration 1. Remove the sensor from the exhaust, the sensor needs to be in free air for this procedure. 2. Disconnected the sensor from the LC-1’s sensor connector. 3. Switch 12V supply to the LC-1 ON. The LED will flash a two blink sequence with a 2 second pause during this time. Leave the unit powered ON for 20 seconds. 4. Switch the 12V supply off after 20 seconds. 5. Connect the sensor to the LC-1’s sensor interface connector but do not put the sensor in the exhaust. The sensor must be removed from the exhaust and exposed to free air for this calibration. 6. Switch the 12V supply to the LC-1 ON. The LED will first blink steady about 2 times/second: indicating that the sensor is warming up. The LED will then start a faster blinking sequence about 4 times/second indicating a Heater calibration. When the Heater Calibration is done the LED will light up and remain solid. 7. While the sensor is still removed from the exhaust perform a free air calibration.
Click to expand...
yes i have a volt booster. I have unhooked it several times trying to find this issue and no change.

Sensor is about 2 years old. I have not calibrated it since i initially did when i installed it.
 
Compared to those on this forum, I know comparatively nothing about these cars but I would do a heater calibration regardless of whether it could remotely be related or not. Don't cost nothin' and not doing one on my car cost me a LOT both in terms of time and $$$ (well spent $$$ but $$$ nonetheless).
 
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