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General Misfire under higher boost

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jpmxrider489

10+ Year Contributor
2,410
146
Apr 4, 2010
pittsburgh, Pennsylvania
I been having a misfire issue. So a little history first. I have ran 25psi on e85 with a 20g without misfires. But the car, has always had a random misfire code that it would throw a few times a year. I clear the code and everything is fine. The car ran fine.

When that motor spun a rod bearing, my 6 bolt swap, 2g head, and kiggly trigger switch was dropped in. I have done a blt to 28psi with no leaks. I want to test higher but cant get a tester coupler to stay on for the life of me. Things that changed from the old motor to the new one was HI Z fic injectors, hx35.

My issue is a stutter at higher boost like 20 psi. I can do a pull and hold 10psi fine without issues. I have replaced my fairly new ngk wires with brand new ngk wires. I have tested my coil and it measures within spec. I have tried ngk bpr7es, bpr8es, bpr6es, br7es, and br8es. I have played with the gap from 025 down to 018. The problem doesnt go away. Now is there anything else I should try and check?

The kiggly trigger was to make this so I'd didnt have to do any wiring. I am also using a 95 cas behind the cam gear. When the stutter happens, I dont get a cel. I dont have a way to confirm a misfure other than jumpy rpm in my logs.
 
I dont have a way to confirm a misfiure other than jumpy rpm in my logs.
Curious if you can feel the misfires when they happen or if the jumpy log is what you're basing the misfires on. Could the jumpy rpm be a data logging signal issue rather than a true misfire? Is it possible that this is a fuel issue instead of ignition? How are your AFR's, are you running too rich causing misfires? What's the condition of your coils & PTU? Any chance of EMI's causing signal issues with your ECU?
 
How would I go about testing the PTU? The coil pack tested good. I am still in the middle of the tuning process but my afr is 12 at wot currently. I can feel the misfire/stutter. The car shakes or doesnt want to move. The rpm that jumps in the log further proves my theory but I am not sure. What I dont get, is everything was fine with the old motor and now its not. Makes me think possibly the kiggly trigger but I literally out of ideas.

https://www.dsmtuners.com/threads/how-to-test-the-power-transistors.229419/

Just found this.
 
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It sounds like an rpm dependent trigger error to me, the Kiggly trigger wheel might be part of it.
 
Remember that misfires will quickly make an O2 sensor read falsely lean. Is the misfire consistent every time at the same rpm or boost level? Does it get better or worse when the engine is cold or hot? Did you register spark knock with the bpr6es plugs? Did you get carbon fouling on any of the colder ranges when you tried any of those?
 
Here is a picture of the plugs. My AFR in the log does spike when this happens. It is hard to say if it's the same rpm and boost level. Seems to happen in the 15psi range. I don't drive it hard or really at all cold. I wait till the car is warmed up to move it at all. I cant remember the results of the bpr6es. But from everything I read, I should be using the BR series plugs for e85. I could get another set if you think it's a necessary test.
 

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Those plugs don't have very many miles on them do they? Those the 7s? They do look right so far though.

Hard to say anything is wrong for certain at this point, but my next step would be to check the coil housings for spark leak in a dark place. It definitely seems to be a weak spark problem from what you describe. Gap the plugs to .020" and stick with whatever you have in those pics you attached.
 
The plugs are BR8ES. Probably 5 miles on them. I attacthed a screenshot of the log if that helps. How would I check for spark leak? Plugs are gapped at 020 already.
 

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Voltage leaks caused by cracked or otherwise imperfect insulators on any part of the high voltage terminals won't show a problem when you ohm the coil and won't cause issues at low boost. But you can usually see a spark or little lightening bolt dropping off the coil going to metal if you pop the hood and idle in a dark place.

It may not be enough to cause a misfire problem at low cylinder pressures, but will decrease spark energy enough that at higher cylinder pressure there's not enough to bridge the plug gap. Other issues can also cause this, but a leaky coil is most likely.
 
Voltage leaks caused by cracked or otherwise imperfect insulators on any part of the high voltage terminals won't show a problem when you ohm the coil and won't cause issues at low boost. But you can usually see a spark or little lightening bolt dropping off the coil going to metal if you pop the hood and idle in a dark place.

It may not be enough to cause a misfire problem at low cylinder pressures, but will decrease spark energy enough that at higher cylinder pressure there's not enough to bridge the plug gap. Other issues can also cause this, but a leaky coil is most likely.

I ended up finding out my coil was arcing. I had a extra coil and did a stress test to it. The coil was arcing at 35000 volts. Not sure what a good reading is for our cars. I have yet to drive the car with this coil.
 
Have you checked the grounds to the head? I was having spark blow out with a ARC 2 and .020 gap at boost levels it should not be. I added extra ground from head and it cleared right up.
 
Yep, the problem ended up being bad OEM coils which is rare. I actually had 2 that were bad which were my spares. We got a tool from OEM Tools that tested spark stress. Its like 10 bucks. Upon testing we were able to see that the coil was actually arcing slightly. Im not sure if it was bad wiring into the coil pack itself or not. Wires looked old which they are LOL. I ended up getting another coil pack and seemed to solve the issue.
 
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