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2G RANDOM PO300 RANDOM MULTIPLE MISFIRE

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honda_burner

10+ Year Contributor
481
12
Jun 25, 2011
westfield, Massachusetts
So the car is a 1995 Mitsubishi eclipse swapped to a 1997 cas. A little back story, I bought this car as a shell and converted it to a 1997 talon body and put the engine and trans out of a different car into this one. It then sat in a body shop for a little less than a year. I went to take it for its first cruise sunday, and it randomly throws a po300 code and starts misfiring. I shut the car off once and restarted it and it went away. Today I got in it and let it idle for a little bit and after it got up to temp it started misfiring and ran lean. I don't know if the temperature is related or not but that's what popped out to me. The things that bother me are 1) this car was a shell and I never heard it run or know if it had any issues, 2) The car got link and speed density as well as a slew of other new parts before it was running, so that now compounds the prior issue, 3) I put the car together...
If anyone can point me in the right direction at things to look at, I would appreciate it. Seems there is going to be one last hurdle to jump before I get to drive this car.
 
If the car has Link, then go and say 'don't check for random cylinder misfire' for your DTC's (I am not 100% sure if this can be applied to a 97 CAS Swap, I usually hear of this for 1g CAS swaps for the 95). You should be good to go, unless there is some major wiring/spark plug wires hooked up wrong/bad compression issues.
 
It is a socketed 1995 ecu, but I had tom convert it internally to work on a 1997 ignition system. I had read about the "stop looking for misfires" feature and tried looking for it this morning before work in link, but didn't see it. I suspect that might help as well, but I don't know. Usually you have to be cruising for it to trigger misfires on the 1g cas swap, this does it whenever it chooses. Sometimes at idle, sometimes mid drive, this morning it did it after revving it up in place just to grab a quick log.
 
It also goes away, so I'm suspecting its not engine related. It has to be electrical. As stated, it started doing it once and I shut the car off and restarted it and it was fine.

I just updated my profile as well. I haven't been on here much since the updated forum except to read a little.
 
Check what the others before posted first.

2 weekends ago I was getting this same exact p0300 DTC's. Before I continue my car is not my DD. Has had the same gas in there from over winter. Prior to this particular weekend I've never once seen this DTC before. It's always started every time (unless my battery is low or dead). Never really gave me issues.

I'm thinking it may be a mixture of the old gas and new gas i put in prior to me going out to do my cruise logs. After i got some fresh gas I jumped on the freeway. About 5 mins later my CEL came out. Car lost some power. Link told me my DTC was code 1500. Car sounded like a Subaru. Pulled off the free way and popped my hood. Plugs didn't come loose. Coilpack was fine. Turned off the DTC and restarted my car. It ran fine.

Picked up my brother and did about a 45 min cruise log. In that period DTC p0300 came up 2 times. Again sounded like a subaru. Turned the car off. Turned it back on and the code disappeared. That same day after we came back I've changed my plugs to BPR7es's and gapped at about .23-.24. I've done one quick cruise and WOT pull since and no DTC's have appeared.

I"m no expert but in my case I truly think the mixture of gas may have contributed to it. Sounds crazy but that was the only thing that was added to the equation. Since your car was purchased as a shell and sat for some time did you drain the gas? 1 other thing. My brother (who was with me when this happened) was getting the same code on his evo 8. It turns out his injector resistor pack was bad. He took the one off his GVR4 and it took car of his evo.
 
Thanks for the answer. I was thinking power transistor this morning. The shell came with little to no gas in the tank, I did add some before I parked it for the winter, but only about a quarter of a tank. I ran into other issues with the tune and ended up having to tow it to my house. I put fresh gas in it a couple weeks ago because we were running low while trying to straighten the tune out. Also, I have bpr7es's as well. I did gap them prior to install, but perhaps I can check them again.
 
I would not select the option that says do not look for random misfires for the reason that you said the car ran lean when it threw this code, that to me is a reason to be concerned. A random misfire code in my experience is usually due to a vacuum/boost leak or a faulty injector. This car is running on SD, that eliminates a dirty MAF sensor which also could throw a random misfire code.
 
Would shutting the car off make a bad injector correct itself 99gsx? And wouldn't that make one cylinder not work? not multiple? It has a brand new 255 fuel pump. I could try the fuel filter.
 
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