Inconsistent misfire around 2000 rpm

[Nicholas H]

The grounding points all over the car have been cleaned/sanded and a solid connection has been made to no effect on the misfire issue. I did unplug the alternator during a test drive to no effect on the misfire. Attached are 2 log files and the tune file. These log files are from the same day with zero modifications to the tune between runs. The smooth log is from my drive to work and the rough file is on my way home from work. The smooth log i could still tell it wasn't running at 100% but there no bucking and very minimal audible miss. The rough file the car was more audible and i could feel the misfire. I will be going through the files a little bit more to try and find a difference that could be inducing this behavior but at a first glance i have not been able to find anything. If you have any advice please feel free. The crank position sensor is in the stock location (boss on the side of the block, bolted in, reading the 7x wheel that is part of the crank shaft). The only other areas i can think to look next are the grounds or a new set of injectors to see if that at least changes the situation or fixes it.

Thank you,
Nicholas H

[arnold]

I had similar problems. In the end one of my main fuses was not connecting well... .Took me 2 years to find

[Nicholas H]

I'm glad to hear I'm not the only one who has run into a similar situation. It is so frustrating to be so close yet not be able to fine tune everything because it isn't running on all 4 all the time. I may look further into all of the connections in the wiring harness on this car. While all the megasquirt is new, the cars body harness was utilized for key on power, coil power, fuel injector power, and things like that which were reusable. I am also having an issue with a speedo signal to the new marshall gauge. It uses just a vr signal from the differential but the gauge is picking up some sort of pulse when key is on. Tried new sensor and shielded wire but to no avail. Not a priority so I haven't spent a ton of time sorting it out but it could be related. Not sure. But thank you for your input, I will continue to look into the electrical system and hope I find something sooner rather than later.

Thanks,
Nicholas H

[Nicholas H]

At arnold, out of curiosity did u find this similar problem with issues at specific rpms or was it found everywhere in the rpm that you were getting weird problems? With you having had a similar issue, I am going to try to remove any of the key on/power wires temporarily and hard wire the megasquirt, coils, and injectors straight to the battery to segregate the issue and see if I am having a similar issue.

Thanks,
Nicholas H

[Nicholas H]

Hello again, it has been a little while since my last post. I have been living with my issue for what appears to be about a year now. I decided to try a few new things out this weekend to see if i could change the symptoms. I hard wired the coils, injectors, and megasquirt to the battery with a switch in line to turn on and off. This has appeared to help some with the issue of misfires but not completely. They are less common, once every 7 run cycles do i experience audible or misfires that i can feel. When the misfires occur i have tried turning the ignition key off while keeping the ecm , coils, and injectors on thinking something in the car is causing noise but the misfire stays the exact same as before. One instigator of my misfires that i have not mentioned yet is that when i run the engine hard and hit the over boost spark cut, the engine will misfire from that point on very noticeably every time and has always done so even before this hard wire modification. My next test will be to eliminate power from everything in the car except coils, injectors, and ecm and see if misfires still occur. With key off and battery connected to the chassis the head light module, brake lights, and radio receive power and maybe they are feeding noise into the system. I will try to connect the laptop up soon and record the smooth running into the over boost spark cut and misfire mode. I have wondered if a new trigger wheel and sensor could fix my issue but would like to find the source of my problem if it is noise. Has anyone experienced this sort of misfire issue after a spark cut like this before? I don't understand what could cause this.

Thank you for any advice you may have,
-Nicholas H

[Nicholas H]

I believe that I have solved my issue with much more timing advance, 15 degrees in some areas, and also increasing the raw signals seen by the megasquirt and buffering the signal from the battery and temp sensors within the settings menu. I will continue to drive it and see what happens but the car drives better with more vacuum at cruise, the turbo doesn't seem to get as hot due to late ignition, and the misfire isn't there anymore. Hopefully the good luck continues and all runs well.