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LS1 swap into 77 Corvette. Most of everything came from 2000 Corvette. PCM DID NOT. PCM came from a Camaro. PCM has been reflashed to a Corvette tune more than once.
Car will start and idle just fine but no throttle response from DBW. Throttle blade will flutter when you turn the key, but that's it. I have gone through the wire harness over and over. Tried a different pedal...no change.
It all worked at one time. Right after the engine was placed on the frame, we mocked everything up, reflashed the PCM with HPTuners and fired it up. It all worked. I have a video of it. But, I did notice that it would drop the peddle operation after sitting a while and it would have to be reflashed again to get peddle operation back.
Here's what I think: The PCM has bad memory. You can flash a tune into it and as long as it stays connected to power its ok. But, if you disconnect the battery it loses a portion of the tune, specifically the DBW portion. I no longer have access to HPTuners like I did in the past so I can't really prove this, but I have no other explanation.
I am open to any comments. Has anyone ever heard of this? Is there anyone that has a way to test my PCM and/or TAC module? Are there any other tests I should perform to troubleshoot this? Do I bite the bullet and buy HPTuners and if I do that where do I find a Corvette tune?
Last edited by 77 LS Shark; 06-12-2015 at 07:16 AM.
Flash memory is not affected by disconnecting the battery.
Is there communication between the TAC module and PCM. If not, a U0107 DTC will set? The TAC module will disable throttle control if it cannot communicate with the PCM.
After it acts up, if you turn the key off and then back on without starting it, does the pedal operate the theottle. Isthe motor and tune stock other then what was turned off for the swap?
You are running a 12200411 PCM correct?
After it acts up, if you turn the key off and then back on without starting it, does the pedal operate the theottle. Isthe motor and tune stock other then what was turned off for the swap?
You are running a 12200411 PCM correct?
It is the 411 PCM and I don't think the tune is stock. Since this PCM came from a Camaro the new tune flashed into it is supposed to be a Corvette tune taking into account my mods. Just something to allow me to put a few miles on the car before dyno tuning. I have no way of confirming the tune in the PCM.
The pedal will not operate the throttle in way at this point. It has in the past but not know.
Flash memory is not affected by disconnecting the battery.
Is there communication between the TAC module and PCM. If not, a U0107 DTC will set? The TAC module will disable throttle control if it cannot communicate with the PCM.
Any other DTCs?
I'm getting a P1518 DTC which is serial communicatioin between the TAC module and PCM. I have an Oscope and will confirm this. I did this before too, and I could indeed see the data on the lines. I'll do it again though.
After it acts up, if you turn the key off and then back on without starting it, does the pedal operate the theottle. Isthe motor and tune stock other then what was turned off for the swap?
You are running a 12200411 PCM correct?
I must correct myself here. I just noticed that I DO NOT have the 12200411 PCM. I have the 09354896 PCM. It is my understanding they are interchangable.
Went back to my tuner guy and he double checked my PCM tune and verified its for a 99 Vette. He happened to have another PCM handy and let me take it to try, No luck. So its not the PCM or pedal, and I don't think its the wiring. That leaves the throttle position sensor, throttle body motor and TAC module.
Well...I don't know what I did but it started working. I was doing some voltage checks, everything was checking out just fine. Hooked everything up and jumped in to start it and scan for codes and it just started working. Go figure?!
Nice, electrical gremlin. Hope it has been evicted.
Well, you're right. It is an electrical gremlin. I started putting everything back where its supposed to go and lost the throttle again. I'm gonna have to unwrap the wiring harness and give all the wires in question a good inspection. Still open to any suggestions.
Sonovabitch! I think I got it! When I built the cable that goes from the pedal to the TAC module I referred to the following drawings from ChevyThunder.com
Looks to me that you would just match the ends pin for pin. WRONG! Take a look at the actual schematic (and its from the same website):
Everybody see what I'm getting at? This has got to be my problem. I'm 99% sure I built the cable matching pin for pin. A to A, B to B, C to C etc... I'll be checking this when I get home tonight.
What kind of logic did you use to think that A should go to A. EVERYONE knows K goes to A and A goes to F. /sarcasm. Sorry. :-) I hope that's your problem.
Well, I'm not sure what that schematic I referred to is for, but it's not for a Vette. Turns out the drawings are correct and the schematic is for something else. I cross-referenced this info against other sources and you really do build the cable pin for pin. The Vette pedal has no "pin H" like that schematic is pointing out.
Back to the drawing board. I have some sort of intermittent connection I guess. Very frustrating to say the least.
I noticed that the year/car/truck labeling is all messed up on the diagrams on that web page. For example, only 2000-2002 truck DBW is similar to early Corvette DBW(except pins E & J are swapped at the pedal). The trucks changed for 2003-2005, then again for 2006-2007 Classic, and again for 2007+(6 pin).
You would have codes for pedal circuits if the pedal wiring was messed up.
So I worked on the car all day today and here's whats going on. If I clear all the DTC's everything works just fine. As soon as I turn the key off it throws a P1518 PCM to TAC module circuit. Erase that and all is well again...and so on.
I made sure I have constant voltage at the PCM, pins 20 and 57 on the blue connector. Ignition voltage at pin 19 blue connector and TAC module. Grounds are good.
Thoughts?
Last edited by 77 LS Shark; 06-19-2015 at 07:39 PM.
P1518 is most commonly caused by a poor engine harness/TAC module ground.But there are other possible causes.
Thanks for that document. Checking the grounds was the first thing I did this morning. Used my dremel to really clean up the connections and make sure i have metal to metal contact. The negative battery cable is new and the engine to frame cable is new.
It only throws the code when I turn the key to off. Is the tac module supposed to have battery or ignition voltage?
06-12-2015, 06:49 AM
Have you ever heard of this?? 
