Random Misfires Please Help!!!
Random Misfires Please Help!!!
I am having a strange issue with my car. Ever since I picked it up after the motor build it has been doing something strange.
The issue occurs randomly, but there is a pattern to it. For one, it always happens at higher speeds, for example on the highway at 60+ cruising. I will be at 60 mph in 5th gear for example, press the gas to accelerate (usually not even leaving vaccuum) and it will accelerate for a second and then misfire hard. There is a loud, audible, "BR-RR-RRR" sound, and the car falls on its face and I have to lift off immediately. There are other times when I will just be leaving a stoplight and the issue will surface for no reason in third or fourth gear. It seemed like the issue was load related (as in 1 specific load, phantom knock), but it happens at 70, 80, 90, 100, and above. There are severe misfires but usually only a count or two of knock. The ECU is not really pulling timing before it or anything it just misfires hard without warning and then I lift off.
I thought the issue was 2 things at first. Plugs/Tune. I was on a stock map for my break in. Even with 0 boost the issue occurs frequently and for my 1500 mile break in it was a constant issue. However, when the plugs were changed for fresh iridiums, nothing changed. Didn't change the gap at all. The car runs/idles fine, has 150 psi across on compression, and the only SES light is P0300. Also, Nick @ DTM put a tuned map on there and while the issue is a bit less apparent now it still exists. A stock map on a stroker/built head/turbo kit probably would cause some problems, but even with changes made to the map it wouldn't go away. Nick couldn't get it out with tuning.
I did some logging but it didn't tell me much. It seems as if the car is running fine according to the logs, except when the incident happens but no significant changes occur in anything showing the cause.
Where do I start? I have a DLi and the issue occurs with and without it. Honeycomb on the MAF is ok (I heard this may cause a similar issue). Any suggestions on what to check? Sorry for the long post but without a good explanation it wouldn't make sense what is happening.
The issue occurs randomly, but there is a pattern to it. For one, it always happens at higher speeds, for example on the highway at 60+ cruising. I will be at 60 mph in 5th gear for example, press the gas to accelerate (usually not even leaving vaccuum) and it will accelerate for a second and then misfire hard. There is a loud, audible, "BR-RR-RRR" sound, and the car falls on its face and I have to lift off immediately. There are other times when I will just be leaving a stoplight and the issue will surface for no reason in third or fourth gear. It seemed like the issue was load related (as in 1 specific load, phantom knock), but it happens at 70, 80, 90, 100, and above. There are severe misfires but usually only a count or two of knock. The ECU is not really pulling timing before it or anything it just misfires hard without warning and then I lift off.
I thought the issue was 2 things at first. Plugs/Tune. I was on a stock map for my break in. Even with 0 boost the issue occurs frequently and for my 1500 mile break in it was a constant issue. However, when the plugs were changed for fresh iridiums, nothing changed. Didn't change the gap at all. The car runs/idles fine, has 150 psi across on compression, and the only SES light is P0300. Also, Nick @ DTM put a tuned map on there and while the issue is a bit less apparent now it still exists. A stock map on a stroker/built head/turbo kit probably would cause some problems, but even with changes made to the map it wouldn't go away. Nick couldn't get it out with tuning.
I did some logging but it didn't tell me much. It seems as if the car is running fine according to the logs, except when the incident happens but no significant changes occur in anything showing the cause.
Where do I start? I have a DLi and the issue occurs with and without it. Honeycomb on the MAF is ok (I heard this may cause a similar issue). Any suggestions on what to check? Sorry for the long post but without a good explanation it wouldn't make sense what is happening.
I'm not going to buy a $1000 ignition system which "may" fix the problem. There is no reason the car should be misfiring hard at 70 load. The stock coils and DLi (assuming neither is defective) should be able to handle that.
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bump for more help. Wouldn't a bad coilpack cause it to run/idle poorly everywhere else besides where my problem is? Or is it possible the problem won't surface till higher load. I would assume a coil is either good or bad, not "dying". Am I wrong?
Read this, many people have had this same issue. I'm having same problem after installing a twin disc clutch. I also had a different problem that felt like a missfire under hard acceleration which was solved by replacing a failing Walbro fuel pump.
https://www.evolutionm.net/forums/sh...issfire+issues
https://www.evolutionm.net/forums/sh...issfire+issues
Last edited by mojo; Aug 31, 2008 at 08:55 PM.