dhenderz

2015 Silverado with Gen V L83. Have a few other threads posted for tracking down a number of issues on this truck. I've been able to sort through everything (coolant in connector - 5v ref signal issue & bad injector - misfire on cyl #6). Truck runs great now, but have one last nagging issue with the camshaft position sensor. When starting the truck, especially when its up to operating temp, it will crank and crank without starting. Key back off, try and start it again. It will stumble and try to start, but generally won't until at least the 3rd or 4th try. And then when it starts it sets P0340 & P0341. I can clear the codes and the truck will run fine and not reset the codes until you cycle the ignition back off and try to start it again.

So far I have replaced the cam position sensor twice, both times with original AC Delco sensors. I have replaced the sub-harness on the front of the engine that connects the cam sensor (along with the VVT and oil pressure solenoid) to the main engine harness. Absolutely no difference.

The engine has a Texas Speed stage 1 cam with a zero degree lockout installed. The ECM is seeing the trouble code for cam over advance, but the ECM tune has that turned off so it does not set the MIL. Is it possible the zero degree lockout or stage 1 cam is causing an issue with the cam sensor? I cannot imagine why, but just asking. The reluctor wheel on the cam is OEM.

dhenderz

Maybe one more question. What does the ECM do with the camshaft position signal? Is it only used during cranking/starting? Just trying to figure out why the truck runs so well once its started and I clear the cam sensor codes.

G Atsma

The cam sensor gives the ECM a heads up on where in the cycle the engine is. It would otherwise take longer to start while the ECM tries it out both ways.

dhenderz

Thanks, I saw something similar on another forum. So once the ECM 'knows' whether the cylinder is at TDC or BDC and it syncs with the crank position sensor. So then once the engine starts, does the ECM use the crank position to run the engine and ignore the cam position?

From what I've read, if the ECM is not getting a cam position signal it will fire the plugs & injectors at TDC - not knowing whether that is actually TDC of compression or exhaust. If the engine does not start, the it tries again at 360deg of crank rotation (the next TDC for that cylinder) which should then be compression stroke. I believe it is this 'trial & error' that causes the extended crank time before the engine will actually run.

Really this is all just interesting, background technical info. Doesn't solve my problem, but does perhaps help explain why once the truck is running it runs great. Seems I still need to find out why the ECM is not seeing a cam position signal.

G Atsma

It's actually about whether it's on the compression or exhaust stroke, or more precisely, which rotation of the two necessary for the Otto 4-stroke cycle to function.

dhenderz

Quick update. Problem is solved. Looked at the cam counts thru HP Tuners. Was getting 1 or 2 at each crank cycle and nothing once it started. I spent time double checking the wires from the cam position sensor connector (at the timing cover) and ECM. All checked out fine. I had a new ECM already programmed and ready to install. So I thought no harm in trying. I installed the new ECM. Cam counts back to normal. Truck now starts immediately and runs like a champ.




Maybe some quick background just for reference and in case someone hasn't read the other thread I have posted. After the engine removal, rebuild and reinstall I was fighting a number of trouble codes. Most notably were a number of codes tied to the 5v ref signal being out of range. Checking several sensors that use the 5v ref signal confirmed the circuit was running at 7v or greater. The biggest issue this caused was the fuel rail pressure sensor was indicating over-pressure, this would cause the ECM to initially go into reduced power mode and within a few minutes to shut down. Then it would not restart because it would not signal the high pressure fuel pump to run. Thus not pressure to operate the injectors and no start.




After a ton of trouble shooting (and money and parts) I eventually tracked the issue down to coolant in the harness (female) side of the connector at the front of the engine that connects the main engine harness to the sub-harness that feeds the cam position sensor, cam VVT solenoid and oil pressure solenoid. The feed wire for the oil pressure solenoid is 12v. And he coolant that we splashed into the connector was just enough to allow it to short across the 12v solenoid feed and 5v ref signal (which is there for the cam position sensor). Taking this connector apart, cleaning it and reassemble solved the 5v ref signal issue and all of the associated trouble codes (fuel rail press, barometric pressure, etc). But I was continuing to get the cam position sensor codes P0340 & P0341. These last 2 codes just wouldn't go away.




I am going to theorize here and guess that the ECM got damaged by the 12v arcing across to the 5v ref signal, specifically the cam position circuit. None of the other 5v ref signal issues & trouble codes remained after I cleaned the coolant out of the connector. I think that since the actual source of the arcing was at/across the cam posn sensor signal, that it burned this circuit in the ECM. Just a theory...




So the good news is everything seems to be solved and the truck runs strong.