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1G Car misfire after warm, sometimes randomly.

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CLeMMeR

10+ Year Contributor
873
0
Jul 10, 2011
Pottstown, Pennsylvania
Whats up guys. So as the title states I have a misfire when the car is warm or sometimes randomly. Sometimes is a little hesitation at low rpms when I first got the car, but that seems not as bad after everything Ive done so far. It also cuts out or stutters above 4-4.5k rpm. NO CELs. A quick background on this car. I bought it 2 weeks ago for 1000 dollars, it was sitting for 2 years in the guys yard as he bought a new car and didnt drive it any more. So here is what I have done so far.

NGK BPR6ES Spark Plugs Gapped to .28.
Wires
Air Filter
Oil Change
Fuel filter is going to be done Wednesday.

Im going through the maintenance guide as we speak so I know what to do so far which I'm addressing. and have yet to do. The car does have a boost leak I'm assuming so i am doing a test this week to find it. My boost gauge reads -12 to -17 vacuum at idle. -22 on deceleration. Car boosts to 9psi. Seems like the car spools around 3k rpm The car is mostly stock with only a aftermarket exhaust.

Now I had a "aha, oh shit" moment to rememebr that there was a sensor unplugged on the car. So I just went out to the car like 10 min ago to take a picture of it, then after some more looking around I noticed 2 more sensors unplugged which I have no idea how I missed before, feel kinda like an idiot but. What exactly are these 3 sensors? I think one is the knock sensor which could cause the misfire in the first place, correct? Why it would be unplugged I have no idea. I'll post back after the BLT and if I remember anything. Thanks Guys!

First sensor I found
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Second sensor I found, which is this the knock sensor? Has 2 wires coming from it
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Third and final sensor I found, no idea what in the hell this one is
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Last picture looks like the coolent temp sensor if it's by the thermostat can't tell check your thermostat for a missing sensor heres a link to a thread scroll down abit tho and check the picture out http://www.dsmtuners.com/threads/6an-to-thermostat-housing.473417/ ,

First picture is for the egr thermal sensor if im not mistaken I posted a picture of what the sensor looks like ,

An is the 2nd picture a black and white wire? Looks like knock sensor pigtail if it's black and white can't be anything else really
 

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UPDATE: Changed the spark plugs again just to be sure, old one after 15 miles they looked black already. Put in new BPR6ES gapped to .032.
Changed the fuel filter and still no change.
I took a trip and it ran great, better than usual, no issues. I go to get back in the car an hour later and it would barely start and stay running. Took a couple of turns to start the car, I had to constantly give it gas to keep it running. Sounded like a retarded Harley or a subie. Was bucking in low RPMs and I'm assuming it was running on 2 cylinders, had almost no power. Car usually runs fine until warmed up. I'm moving onto replacing the coil pack and Power Transistor. I read that when the car warms up and can get hot that the PTU can fail, making the car run on 2 cylinders. Still no CEL. ECU was pulled and looked fine. Will give update after Coil pack and PTU is replaced. Any suggestions is appreciated.
 
long as you have your temp and knock sensors plugged in, then i might start looking at an fpr or injector issue. especially if it has a hard time starting after sitting, seems like the plugs might be getting fouled from excess fuel. but thats just a guess.

you could always swap out the PTU, but id start checking individual plugs to get a better read first
 
I cant find the link at the moment but I think It was snowboarder714 that did a write up on all the electrical connectors for dsm. did you check if the it was actually only running on 2 cylinders that will help you diagnose the issue im currently having an issue with an intermittent drop of 1 and 4. to check if your running on 2 cyl pull plug wires 1 by 1 and if you pull one and it doesn't change the idle you know its not working. if your getting spark on all 4 then pull up on the injector plugs one by one and make sure the idle changes. yes what I keep reading for 2 cyl dropping is typically coils, ptu, wiring on either. or the cas or ecu. I just posted an update to my post asking about swapping my ecu ive checked all the above and haven't figured it out yet. if you have a multimeter there is write ups on testing each so you don't have to just throw parts at it. definetly gotta fix the boost leak if you have one that could cause a lot of running issues and the black look on the plugs.
 
Back again guys. Scrap the sensor and plug stuff from the first original post. Car now has a new coil pack and Power Transistor unit and fuel filter. I put in a Engine Coolant Temp sensor today as well. Still has a misfire like crazy. Next I'm only thinking is possibly leaky caps in the ecu or injectors aren't firing right? I pulled the injector clips to see if idle drops and it doesn't drop on cylinder 2. Every other injector drops idle like it's supposed to. I will include two videos for any more help or suggestions, I'm hoping for something. Thanks guys.

Startup
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And after 10 min. Car will barely stay alive like it's on 2 cylinders.

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Do you have a volt meter ? Ohm the injectors and see what you get mine was worse when hot, the ohms went to I think 70 ohms? When they should be around 2-5 ohms it I got no cel either
 
Okay guys so I took a meter to the injectors. Some were close to spec but the thing that stood out was cylinder 2's injector had absolutely no reading at 0.0. And I switch the plugs as suggested but the problem didn't follow, cylinder 2's injector still did not drop idle. I tapped the injector and still nothing so Im guessing that maybe the injector is completely dead and causing the misfire. Im hoping still nothing is wrong with the ecu which I will probably swap out to test.
 
yeah sounds like they are dirty and stuck open. my advise would be to take care of that as soon as possible. same thing happened on my sti and i blew out the piston rings under boost.
 
you can also take a 9volt battery and run leads to the injector to try and open it back up if thats the case. I use alligator clips and leave one loose to tap it on the connection. If you can get it to click every time you opened it. Had to do this on my 1850s that sat for a year and now they run like new. Not saying this will permanently fix your issue but it may.
 
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