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GVR-4 Intermittent Misfire at idle

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eDeclpse92

10+ Year Contributor
351
4
Sep 6, 2008
Belleville, Illinois
I am chasing a problem that keeps eluding me. I have a misfire at idle and in low rpms under load. After that, the car pulls just fine after about 3000 rpms. It is a 91 galant vr4 completely stock. i checked with a timing light on all four cylinders and just shined it on the firewall and you can see each cylinder misfire intermittently. Things I have checked:

Switched out with known good coil pack, power transister- still misfires
o2 sensor CEL code- replaced with new one
new plugs and wires
compression and leak down results are very good.
boost leak test is done and no leaks were present
Timing is at 5 degrees BTDC
crank and cam pulley marks line up with the timing belt
injectors were cleaned.
new gas

Any suggestion to what this might be will be much appreciated, or the next step in diagnoses. Could a CAS do this?

Thanks!
 
Check your base fuel pressure. Make sure sparks plugs are not over torqued. If spark plugs were over torqued or dropped, the ceramic porcelain could have cracked. Make sure spark plug wires make a good contact to coils and spark plugs. Some after market wires may not make a perfect seal/contact. Verify spark plug type and gap with a real filler gauges, not one of those round ones.
 
Spark plugs are installed correctly and I have had 2 sets of brand new wires on it. (one set NGK and the other from Oreillys). Spark plugs are gapped correctly before installing all of them with a feeler gage (.028 I believe). I could check fuel pressure but at higher RPM's when the demand is higher for fuel, the car runs great. So I was knocking that option out. If I didn't have pressure, I would see it more at higher RPMs.
 
Anyone have this happen to them before?? I don't want to start throwing parts at a car... Any more advice on where to look next?
 
Is it a consistent misfire at idle? Do you misfire while cruising at low rpm's?
 
Also check that your 2 wire temp sensor (on thermo housing) for the ECM is connected and working as this could making it run richer or leaner than it should be.
 
I only misfire under a load at low rpm's. High rpms is fine and it isn't a constant misfire. At idle, when you hook up a timing light to any of the cylinders, it will fire consitently and then misfire every 4 seconds or so. I tapped on the CAS the other day while it was doing it and it stopped misfiring for a longer period of time. Sounds like that may be the culprit. I'm going to the junkyard tomorrow so hopefully I can find a couple of them for cheap. The temp sensor is hooked up currently. I think it's the one wire temp sensor that you are talking about though. That's the one that resistance changes on and tells the ECU what fuel mixture to run.
 
You have a 1g right? The single wire is for the engine coolant temperature gauge, the two wire is for engine coolant temperature sensor for the ECU. This is for my 90 talon tsi, unless the following years are a bit different.
 
Ok, that makes sense. I do have something plugged in. LOL I'll have to check because the housing is different than a 1g dsm. The galant has a different water outlet and different sensor locations. I'll have to try and find a good one from the forums somewhere. But I put an osscilliscope up to the CAS and was able to see the proper step waves so that is working correctly. Took the ECU out and saw someone has been in there before to repair it and their work was questionable. A couple cold solder joints and a mosfet was replaced. Also some corrosion on the caps. Maybe this could cause the misfire?
 
Have you checked the resistance of your injector pack located on the firewall in the engine bay. there suppose to be 5.5ohms-6.5ohms using pin 3 and the base for all other pins... top of connector where it locks in starting under to the far right looking at the open face is #3
 
I am getting ignition misfire. I can see it with the timing light. Will the injector pack cause an ignition misfire? I thought they ran independent of each other. Pulled the ECU, someone else has been in there and gave it to a buddy to re-solder bad joints and clean it up. Still does the same thing.

Edit: I have seen threads for this issue that are exactly what I am experiencing, but they never give a solution. I purchased tunerpro with a cable and I will monitor the engine to see exactly what is going on and hopefully I can see where the problem lies. At idle, with the ecu ungrounded, the timing jumps all over the place. Maybe a bad knock sensor or it's seeing phantom knock? Haven't heard of that problem on a stock car though. I will update once I get the program, learn it and figure out the problem. If anyone has any issues like this, please share, I am open to suggestions.
 
I been outta the DSM game for awhile but i was pretty familiar with Link at a time and DO remember idle timing jumping around. It's a normal thing. You can lock it at 5*, iirc, but that's for other purposes and def not for normal operation

One thing that kept getting me was after i put maybe 1,000 miles on my build i noticed the misfires getting worse and worse up past 40lbs/min. It stumped me for a long time.
Finally found it. Leaky #2 valve. Head was brand spankin new, just put together poorly as so commonly occurs with local machinists. (and SIM!! Never EVER shop with them!!!)

But you? You did a leak down and came back good. You've tested literally everything besides running a fuel pressure guage in the car while accelerating. That would show a bad hose or faulty afpr. Bad afpr diaphragm is a rare thing and you'd notice it at idle most likely. Hell, it might not even start. But a bad hose running boost source to the nipple on the afpr? possible.
Check wiring at the pump. Check fuel filter.
Don't want too much voltage drop but you will get some, it's inevitable. Harder the pump works the more current it draws. Current goes up, voltage goes down. You can swap those 2 around, basic electronics.

You've probably tested everthing i mentioned. ALso, one last thing: Plug wires are finnicky little bastards and will be bad outta the box. Seen it before. Injector wires or resistor box for the injectors? They can be intermittent as well. Will cause a severe miss at idle usually though. In my findings. Not like what you're having

Good luck my friend
 
Thanks for the advice boost97gst. I am still waiting on the cable and tunerpro to come in the mail so I can monitor what is going on. As far as the timing jumping around as you described, how much did it jump at idle? Mine is jumping between 5 and 10 BTDC pretty quick. I thought that was a little erratic which is why I may be leaning towards a bad knock sensor. As far as bad fuel pressure goes, wouldn't I see that problem at higher RPM's due to not enough fuel coming to the rail/ injectors? I have a known working spare FPR that I could swap out real fast. I am just wanting that cable to get here so I can see what my engine is doing and hopefully I can narrow down the issue.
 
I know it has been a while but I would like to post the solution that was found for this misfire.

I took my car to Genes automotive in Highland IL and he was able to figure it out. 3 things were wrong when my car was misfiring.

1) My coil was arcing before the plug wire to the manifold
2) Very dirty injector in one of the cylinders (should have caught this as I noticed the spark plug was burnt in this cylinder when I initially bought the car)
3) Fuel Pressure Regulator that would not hold pressure and bleed off.

Besides the typical ISC idle jump for a minute on start up, the car runs and pulls extremely well for it's mileage and being stock.

Thank you everyone for your suggestions and I hope this helps someone out one day!
 
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