Tools to analyze and/or rehabilitate programming modifications to a California C5 Corvette PCM
I have this 1998 Corvette which has been reprogrammed by some local tuner guy, but in his "tune" he set certain monitors not to run among other dishonorable departures from decorum and normative behavior. I'm in the L.A. area and this has left me with a vehicle which won't pass state emissions testing.
My larger question is that of diagnostic tooling: how could I best figure out what Mr. Tuner did to this car and then how could I restore it to righteousness with the state of California? EFI Live? HP Tuners?
As more and more local vehicles receive these backalley "tunes" (done without a dyno so I can imagine how the fuel trims were set at for example part throttle) and as the state clamps down more and more on their emissions testing protocols it seems to me that this type of task might become increasingly common.
How would you suggest I proceed? Are you seeing/doing this kind of work?
Flash it with TIS2WEB and it’s back to stock.
That was my first instinct Thanks!
Allen's right, flash back to stock w/ TIS. We see a few of these a year, usually they come in needing a state inspection, but all the one's we have seen also require hard parts (cats/ AIR pumps, O2 sensors, ect) along with the OE software.
That's my fear Thanks!
I wouldn’t go flashing a modified vehicle with stock tune period without some written agreement from the customer that this car may run worse... he may not pass inspection now but in his head his car “runs great” if you put a stock tune on a worked ls there is a good chance this thing won’t idle right much less drive properly. It will be a hard sel afterwards where you are trying to tune things…
What an important warning Thanks!
As others have said, flash back to stock using a Tech2 or in theory possibly a J2534 device if they support this vehicle. Also be aware that frequently other parts will now need replacing due to either driveability issues or that the vehicle is now running proper diagnostics and starts setting codes. I haven't run into it on a GM yet, but some tuners will also lock down the PCM to prevent it…
Thanks so much Phil!
David- Manuels suggestion is the first correct step. Typically when these things are tuned, they have some sort of aftermarket parts on them . You have to have a detailed talk with the customer prior to returning the PCM to stock or you may end up with a problem vehicle. Also FYI, Etuning is a thing now. A dyno is becoming increasingly unnecessary as Etunes have proven to be very reliable and…
I'll look into this ETune thing- thanks for the tip!
Hi Dave, Do you have the PCM removed? If so, upload a pic of the connector. We can have a look at what’s been modded if I have the right connector for off-board operations.
Hi Scott Thanks! But it's still in the vehicle. In fact I had just pulled the trans out to get it rebuilt when... they closed the school (!)
Ok, you should be able to get the cal ID’s and checksums and compare those to what tis2web.service.gm.com/tis2web reports. You will then have an idea of which calibration segments have been modified. If you’d like me to accompany you on a trip down to the school and read the controller let me know.
Thanks Scott let me get the trans back in this rascal and I'll get back to you Thanks! Dave
Hi David, What has been done with the vehicle? Do you have any idea other than a 'tune'? The catalysts deleted. camshaft, cat back exhaust, different heads,...?? If this vehicle is stock I would put the programming back to stock using TIS2Web. If it's been modified I would use either of the programs you mentioned and upload the calibration files from the existing PCM to a laptop used for…
The vehicle looks completely stock which makes me think the tune is the only modification. But I am a little nervous that I'm gonna find the "tune" is really there to hide some fault in some emissions control system. Thanks!
Hi David, I've got the procedure from how my friend handles this. He'll upload a copy of the tune that's in the vehicle currently. In the case of a car that is stock, he'll have the stock files flashed by a local mobile guy. He can upload the factory calibration files so he'll have a copy of stock and the modified tune, if any changes need to be made. Based on what you're saying he's probably…
You're right about the need to fix any underlying issues that the "tune" may be hiding. The car runs great tho I'm not overly convinced that it's really stronger or faster than a stock tune. My analogy is amplifiers: an amplifier that's 10% louder will be barely noticibly different. Likewise I don't think that a 10% increase in power (35 hp) will really be an earth-shattering improvement. I'm…
David why not just get a used ECM for it and program it using TIS. That way you can see how it runs with the stock calibrations and if it needs more parts/work to make it run properly.