My buddies C5 is having some serious start-up issues. It usually takes two tries to actually kick over and run. But as of last week, we cranked it like normal and the car backfired out of the intake, not exhaust. Now every time you crank the engine the RPM's automatically start speeding up. It will climb up to about 3500-4000 RPM and then shut itself off. Very confusing .

Need to know information: The car has a stroked LS2 with a procharger. It ran great with no problems until now. The only code that it displayed that might cause problems was a "camshaft position sensor" code. We also scanned the car and discovered that the throttle position sensor was sitting at 16% even when the car was off. Don't know if that is a problem or not. I don't imagine that 16% throttle will provide 4000 RPM.

What steps we have already taken: We already scanned the car with the OBD and with HP Tuners. No really big significant issues. We also removed the throttle body and took it apart to inspect it. Everything looked good. We also did and very detailed inspection of all wires and vaccum hoses. Everything looked good. And just for laughs, we tried the idle re-learn proceedure as well, no love.

Now we've reached a stopping point, we don't know what is left to inspect that might cause a problem like this. Has anyone ever heard of a similar problem? Any insight would be greatly appreciated. Thanks

 

WOW! Over fourty views and not one response. Guess I'm not the only one confused.

 

Don't have manuals with me right now, is there a way to test the cam sensor without removal? Also, on the TPS, does it stay at 16% once you start? I was under the impression that turning the key would result in the blade closing then a reset to zero of the TPS and then a fixed position for the start. Could be off here, but that is what has been explained to me.

 

Not sure about testing the cam sensor, however we did find some information about the wires on the harness being in the wrong position from the manufacturer. And as for the TPS, we really can't start it at all due to the high rev's. Currently we are digging into the PCM and the tune to see if we can discover any flaws. Thanks for the input.

 

Look at the throttle body plate. If it back-fired through the intake it may have bent the plate & that is where the issue is. Just a thought.....

 

 

Yeah, that is what we thought too. I completely disassembled the TB to inspect the plate, shaft, teeth, etc. Everything looked "A" okay. After a little more troubleshooting/ disassembling, I believe we narrowed it down to something in the timing chain or cam sprocket. Hopefully we nailed it and we're hoping to have the car back on the road next weekend. Thanks for all the help.