Am I Possibly Running The Wrong PROM....?
06-25-2009, 03:18 PM
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Am I Possibly Running The Wrong PROM....?
Guys, just got my hands on a 1990 GTA with an automatic 305 TPI. Since I had it, the stock injectors crapped out on me so I temporarily replaced them with a set of 24 pound LT1 injectors. Since I had the car, the speedometer has not worked, well, would work occassionally, but the majority of the time it was completely dead. The only codes the car has ever thrown, repeatedly, is code 24, VSS. I was planning on getting to the VSS sensor down the line, but in the mean time, I wanted to see how rich I was running with the LT1 injectors so we hooked up a scan tool.
BLM's are at 109, with the intergrator at around 140'ish. Oddly enough, the engine runs fine rich, no black smoke, and no code 45, and other than a slight surge at idle, there's no problem. However, what we did notice on the scanner is that the ECM is commanding 600-RPM with the transmission in Park. It does this throughout, as if the ECM doesn't even see Park whatsoever. I thought maybe there might have been a bad hookup by the shifter, but everything looks to be okay. Is it possible that the former owner was running a manual chip, being that 600-RPM is commanded whether in Park or in gear, as well as the speedometer not working? I figured before I pull the ECM out, I wanted to check if there was something else that might have caused the ECM not to see a Park condition. If there is nothing else other than the wrong prom, would anybody be able to tell me what to look for on the prom itself (serial number) to help distinguish if I'm running the wrong one? The only other symptom is that, with the battery disconnected, then reconnected, the engine runs very strong and idles flawlessly, for the entire time its running. However, once the key is turned off, then turned back on again, the engine will stall at deceleration, whether on a turn, or coming to a full stop. The engine will also surge horribly when restarted, until it eventually dies. However, when the battery is disconnected then reconnected again, she runs like a champ. It's only when the key is off, then on, thereafter.
IAC counts, TPS, O2 voltage, MAP etc., are all on the money. I thought maybe the larger injectors might be causing the surge, but it doesn't surge at all when the ECM is reset by disconnecting the battery, even for hours, and at high temps, it runs fine, it's only when the key is off, then on again. The injectors will eventually be tuned, but they don't explain the loss of Park though. Any ideas? Thanks.
BLM's are at 109, with the intergrator at around 140'ish. Oddly enough, the engine runs fine rich, no black smoke, and no code 45, and other than a slight surge at idle, there's no problem. However, what we did notice on the scanner is that the ECM is commanding 600-RPM with the transmission in Park. It does this throughout, as if the ECM doesn't even see Park whatsoever. I thought maybe there might have been a bad hookup by the shifter, but everything looks to be okay. Is it possible that the former owner was running a manual chip, being that 600-RPM is commanded whether in Park or in gear, as well as the speedometer not working? I figured before I pull the ECM out, I wanted to check if there was something else that might have caused the ECM not to see a Park condition. If there is nothing else other than the wrong prom, would anybody be able to tell me what to look for on the prom itself (serial number) to help distinguish if I'm running the wrong one? The only other symptom is that, with the battery disconnected, then reconnected, the engine runs very strong and idles flawlessly, for the entire time its running. However, once the key is turned off, then turned back on again, the engine will stall at deceleration, whether on a turn, or coming to a full stop. The engine will also surge horribly when restarted, until it eventually dies. However, when the battery is disconnected then reconnected again, she runs like a champ. It's only when the key is off, then on, thereafter.
IAC counts, TPS, O2 voltage, MAP etc., are all on the money. I thought maybe the larger injectors might be causing the surge, but it doesn't surge at all when the ECM is reset by disconnecting the battery, even for hours, and at high temps, it runs fine, it's only when the key is off, then on again. The injectors will eventually be tuned, but they don't explain the loss of Park though. Any ideas? Thanks.
Last edited by TPI-454; 06-25-2009 at 03:21 PM.
06-25-2009, 09:02 PM
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Re: Am I Possibly Running The Wrong PROM....?
Update;
Turns out that I very well might be running the wrong prom afterall. After closer inspection underneath the shifter revealed that the car originally was a 5-speed manual, which is all starting to make sense now. The speedometer never really worked right, or even worked at all, for that matter. The idle is always 600-RPM, and the surge only occurs when the tranny is in Park, not in gear. Not to mention, there are times when the engine won't start at all, much like a cut off switch, as apparently it's waiting for the 'missing' clutch to be depressed. I double checked the prom ID on the scanner, and it reads 3281 (not sure what this means), but either way I guess its time to burn a new chip....
Turns out that I very well might be running the wrong prom afterall. After closer inspection underneath the shifter revealed that the car originally was a 5-speed manual, which is all starting to make sense now. The speedometer never really worked right, or even worked at all, for that matter. The idle is always 600-RPM, and the surge only occurs when the tranny is in Park, not in gear. Not to mention, there are times when the engine won't start at all, much like a cut off switch, as apparently it's waiting for the 'missing' clutch to be depressed. I double checked the prom ID on the scanner, and it reads 3281 (not sure what this means), but either way I guess its time to burn a new chip....
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