Can't track down bizarre misfire issue
Oct 12, 2020, 06:46 PM
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Can't track down bizarre misfire issue
Attaching the EvoScan log files...
When I am in low RPMs (2500-3000) and accelerating slowly with light-medium throttle I am having an extremely strange misfire. It sounds like all of the cylinders are simultaneously misfiring and all of the power is lost until I let of the throttle and get back on it. Never happens while boosting. Only while in vacuum and at lower RPMs. The first time I noticed it was while cruising on the freeway in 5th gear and it seems to get progressively worse.
When I finally got the log of it I am having my injector pulse width and duty cycle drop all the way to 0 while this is happening. o2 Sensor will also show a reading of 0 while this happens.
I've attached two different logs here: the first is the one I finally got today while out driving when it sputters super hard while softly accelerating (18.17.20). The second (18.19.25) is of the idle once I returned and was backing into my driveway when the car started idling super rough (the first time this has happened) and clearly having some type of very consistent misfire.
Spark plugs have been changed and boost leak tests showed no leaks. Car is on speed density.
Please help me out - feeling defeated and in over my head right now since I can't track this down.
When I am in low RPMs (2500-3000) and accelerating slowly with light-medium throttle I am having an extremely strange misfire. It sounds like all of the cylinders are simultaneously misfiring and all of the power is lost until I let of the throttle and get back on it. Never happens while boosting. Only while in vacuum and at lower RPMs. The first time I noticed it was while cruising on the freeway in 5th gear and it seems to get progressively worse.
When I finally got the log of it I am having my injector pulse width and duty cycle drop all the way to 0 while this is happening. o2 Sensor will also show a reading of 0 while this happens.
I've attached two different logs here: the first is the one I finally got today while out driving when it sputters super hard while softly accelerating (18.17.20). The second (18.19.25) is of the idle once I returned and was backing into my driveway when the car started idling super rough (the first time this has happened) and clearly having some type of very consistent misfire.
Spark plugs have been changed and boost leak tests showed no leaks. Car is on speed density.
Please help me out - feeling defeated and in over my head right now since I can't track this down.
Last edited by SecristM; Oct 12, 2020 at 07:27 PM.
Oct 12, 2020, 07:17 PM
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Wondering if this could be my COP system after spending some time reading similar threads. I have recently started getting a LOT of bucking at lower RPMs & when turning as well.
Oct 17, 2020, 10:33 AM
#5
You are getting fuel cut in the logs so its not the COP. To help you with a diagnosis we will need to know the details of all the mods to engine, intake, fueling, and ECU (ROM ID).
For example:
1. Are you on a speed density (SD) ROM? The logs show fuel cut below logged MAP values of 2.1
2. How are you logging and measuring MAP?
3. What units are you using for MAP - PSI or kPa?
4. What type of MAP sensor are you using?
5. Have you checked that your MAP sensor is getting a constant supply voltage (5V) and giving you the expected output voltage for light acceleration which is around ambient pressure (~100 - 120 KPa absolute pressure)
6. Are you on a mass air flow (MAF) ROM? The AirVol logged goes to zero at the same time the fuel is cut. This could indicate a bad MAF signal or a bad MAF if you are in cruise at that point.
Post up the full details of your setup if you want further help otherwise it is impossible for us to give you a diagnosis over the internet.
For example:
1. Are you on a speed density (SD) ROM? The logs show fuel cut below logged MAP values of 2.1
2. How are you logging and measuring MAP?
3. What units are you using for MAP - PSI or kPa?
4. What type of MAP sensor are you using?
5. Have you checked that your MAP sensor is getting a constant supply voltage (5V) and giving you the expected output voltage for light acceleration which is around ambient pressure (~100 - 120 KPa absolute pressure)
6. Are you on a mass air flow (MAF) ROM? The AirVol logged goes to zero at the same time the fuel is cut. This could indicate a bad MAF signal or a bad MAF if you are in cruise at that point.
Post up the full details of your setup if you want further help otherwise it is impossible for us to give you a diagnosis over the internet.
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