This past weekend, at the Cal Club regional at Buttonwillow. First time the car (and me) have been on track in 3 years. I did a full tune up on it, changed the fluids, ran it for a bit in the garage and around the block with no issues.

Morning practice session, and I make it through the warm up lap with no problems, although I noticed that my speedometer wasn't working at all. Didn't think much more about it at the time, but about 3/4 of the way through my first hot lap, I lose all power to the engine. It didn't shut off, just dropped down to idle. The only thing that seemed to bring the fire back was upshifting, and I continued on for another 3/4 of a lap or so, when it did it again. Slamming my foot against the gas pedal to maybe unstick the throttle didn't do anything at all.
The only thing that seemed to bring it back was upshifting (downshifting didn't seem to do anything at all) and even upshifting didn't always kick it back in.

No check engine light or anything. When everything was working, the car was running great, but once or twice a lap, I would lose all GO, and the engine would drop to idle speed, and then a few seconds later, or after an upshift, it would come back.

After practice I tried replacing the fuel filter and fuel pump, but to no avail. I went through qualifying and the race with the issue not going away. My biggest concern was being in the way on track, but as there were even slower H production cars than me, even with the car not working properly, I don't think anyone even noticed.

Finally, after coming in to impound after the race, the check engine light came on. When I checked the diagnostic codes back at my pit, I got the Vehicle Speed Sensor and Throttle Position Sensor codes. I put a meter on the VSS and was not receiving signal pulses back from it, so I'm assuming it's toast (explains the lack of speedometer), and when metering the TPS, it starts out fine closed, at .5v, and increases gradually until it hits about 3.9v where it jumps to 40v, back down to .5v, and then continues on up at 4.1v, 4.2v, 4.3v, etc. I thought it was my meter at first, cuz where would 40v come from, but after replacing the batteries, it continues to do the same thing. I've heard of dead spots forming in the potentiometer, and am assuming that's what's wrong with it.

Okay, so I've ordered a replacement VSS and TPS, but my big question is, would those issues cause the problems I had on track? Could there be something else like a faulty fuel pressure regulator or problem in the ECU? Anyone ever had this happen before? It sucks cuz running it in the garage or around the block doesn't seem to be driving it hard enough to cause the problem to crop up. I don't have anywhere here to try running it full out to see if I've fixed it, and a race weekend is an awfully expensive place to be trying to cess out issues in the car. Help, please! Thanks.

 

we had a customer car acting up on the dyno, there was a break in the wire, and caused strange readings while datalogging. you may have a dying TPS/wiring problem. and a VSS code always made my car run like crap. but the bogging porb you are desc. sounds like faulty tps, or wiring for the tps

 

Thanks.

That seems to be the general consensus; that the dead spot on the TPS is causing the ECU to hiccup for a few seconds. New parts are on the way, and I hope to be back in action, soon. Again, thanks for the help.

 

So, replacing the TPS and VSS seems to have fixed all the problems. The only thing I can really think is that the dead spot in the TPS coupled with the fact that the ECU didn't think the car was moving at all thanks to the f'd up VSS made it drop into idle when the right signals, or lack thereof crossed paths in the computer.

Ran the whole weekend at California Speedway last month without a single burp or hiccup from the car.

Thanks for the help.