Is my PCM bad?
06-06-2009, 04:39 PM
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Car: 1997 LT4 Firehawk
Engine: 350ci LT4
Transmission: MN6 6 Speed
Axle/Gears: 3.42:1
Is my PCM bad?
I hate to hear folks say "your computer is bad, dude", but I think my computer may be bad. Seems like the PCM gets blamed for about everything, from what I've heard, but this time it may be true.
I've got an '87 Trans Am 305 TPI, 700r4. It'll run great for a time...from a few seconds to a half hour, then the SES light comes on and it runs very poorly. It will barely stay running at idle, has horrible throttle response, and accelerates worse than anything I've ever driven. It misses, sputters, detonates, etc. Then, hit a little bump and the light goes off, and it runs great again. The light may come on for a half second, even...it loses all power for that half second, then the light goes off and it runs fine again.
I've got an OBDI reader and if the SES light is NOT on, it tells me there are no codes. If the SES light IS on, it says it cannot communicate with the vehicle.
I've removed/cleaned/reinstalled every ground connection I can find under the hood, and it still does it. With the reader not connecting, I think it has to be the PCM ground, or else the PCM itself.
My plan of attack: remove the Hypertech chip and replace with the original, check PCM ground. If that doesn't do it, replace the PCM with a known good one (Anybody got one for sale?). If that doesn't work, I dunno what to do. Anyone got any ideas? Does it sound like I'm on the right track, here?
Thanks!
I've got an '87 Trans Am 305 TPI, 700r4. It'll run great for a time...from a few seconds to a half hour, then the SES light comes on and it runs very poorly. It will barely stay running at idle, has horrible throttle response, and accelerates worse than anything I've ever driven. It misses, sputters, detonates, etc. Then, hit a little bump and the light goes off, and it runs great again. The light may come on for a half second, even...it loses all power for that half second, then the light goes off and it runs fine again.
I've got an OBDI reader and if the SES light is NOT on, it tells me there are no codes. If the SES light IS on, it says it cannot communicate with the vehicle.
I've removed/cleaned/reinstalled every ground connection I can find under the hood, and it still does it. With the reader not connecting, I think it has to be the PCM ground, or else the PCM itself.
My plan of attack: remove the Hypertech chip and replace with the original, check PCM ground. If that doesn't do it, replace the PCM with a known good one (Anybody got one for sale?). If that doesn't work, I dunno what to do. Anyone got any ideas? Does it sound like I'm on the right track, here?
Thanks!
Last edited by LT4Hawk9; 06-06-2009 at 05:39 PM.
06-09-2009, 06:42 AM
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Car: 1990 IROC
Engine: 5.7 TPI
Transmission: T-56
Re: Is my PCM bad?
The way it's sounding, if you hit a bump and the problem goes away, it really sounds like a ground is loose or the internal componets of the ecm are breaking a connection. I would go through all the schematics and find all grounds, shake them, clean contacts. Have the car started when doing this to see if when you tap the grounds it is fails; then you'll know where your problem is. I'm an F-16 avionics tech and I chase problems like this ALL the time and I do mean ALL THE TIME! It really sounds like one of the two problems I suggested. Multimeter is a useful tool to t/s problems like this
btw, car looks really nice!
btw, car looks really nice!
06-09-2009, 12:24 PM
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Car: 1997 LT4 Firehawk
Engine: 350ci LT4
Transmission: MN6 6 Speed
Axle/Gears: 3.42:1
Re: Is my PCM bad?
That's what I was thinking. I need to get time to work on it, now.
Thanks!
Thanks!
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