Idle Misfire Solved!!!
12-08-2003, 02:16 PM
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Idle Misfire Solved!!!
I think I got it! It it turned out to be the most IDIOTIC thing imaginable!
I was going over the fuel injection harness that's under the dash inside the car, and I noticed a wire going from the cruise control harness to the fuel injection harness. I then remembered that sometime late last year (about the time the misfire thing started up) I was diagnosing a problem with the cruise control. I ran a wire that I thought was at 12V on the cruise harness to an orange wire (12V) on the fuel injection harness. Apparently, I never took it off. Well I just put an meter on that wire and found out that it was freakin' ground! And that 12V wire on the fuel injection harness was powering the fuel injectors circuit. All this time, I was apparently shorting out the injector circuit. But it was on the "upstream" side of the fuse which is why the injector fuses never blew. The short was going right through the ECM. Un-freakin-believable.
The reason I forgot about it is that at about the same time I did that thing with the wire, apparently my PROM burning software got corrupted and I was spitting out bad PROM chips. This was going on until about last March when I figured that one out. At that time I thought that was going to solve the misfire. But when it didn't, I forgot all about that wire and started going after everything else on the vehicle.
Well, I went back to the wrecking yard and picked up another ECM, put it on, and it's idling smoothly again. What a year this has been. I kept telling myself "it has to be something stupid" "it has to be something stupid" "it has to be something stupid", but the apparently the problem simply evaded all the diagnostic equipment known to man.
But at least now I can get down to the business of calibrating for the new cam I put in it. Just the way it stands right now with the old calibration for the ZZ4 cam, this thing runs really hard. It's going to be fun! :lala:
I was going over the fuel injection harness that's under the dash inside the car, and I noticed a wire going from the cruise control harness to the fuel injection harness. I then remembered that sometime late last year (about the time the misfire thing started up) I was diagnosing a problem with the cruise control. I ran a wire that I thought was at 12V on the cruise harness to an orange wire (12V) on the fuel injection harness. Apparently, I never took it off. Well I just put an meter on that wire and found out that it was freakin' ground! And that 12V wire on the fuel injection harness was powering the fuel injectors circuit. All this time, I was apparently shorting out the injector circuit. But it was on the "upstream" side of the fuse which is why the injector fuses never blew. The short was going right through the ECM. Un-freakin-believable.
The reason I forgot about it is that at about the same time I did that thing with the wire, apparently my PROM burning software got corrupted and I was spitting out bad PROM chips. This was going on until about last March when I figured that one out. At that time I thought that was going to solve the misfire. But when it didn't, I forgot all about that wire and started going after everything else on the vehicle.
Well, I went back to the wrecking yard and picked up another ECM, put it on, and it's idling smoothly again. What a year this has been. I kept telling myself "it has to be something stupid" "it has to be something stupid" "it has to be something stupid", but the apparently the problem simply evaded all the diagnostic equipment known to man.
But at least now I can get down to the business of calibrating for the new cam I put in it. Just the way it stands right now with the old calibration for the ZZ4 cam, this thing runs really hard. It's going to be fun! :lala:
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