Fbody P0336 Help needed!

[ErinC]

Here's a short back story on this car. I built a 441 LS7 for this 2001 Firebird 2 years ago. Car ran flawless until about 2 months ago when the customer brought the car back to me. When it throws the P0336, the tach quits working, a rpm spike can be observed on the scanner, and the car runs terrible because of it. If I clear the code the tach will start working again and the car will run correctly for about a minute until it throws the code again.

While trying to diagnose the problem I have swapped crank position sensors (twice), re wired the sensor with new GM terminals at both the sensor and ecm, tried a known good ecm, performed load volt drop test at the ecm, removed the engine to verify that the reluctor had not spun (it has not), run the engine without the alternator(suspected emi), and verified all grounds.

When we did the loaded volt drop test, we observed a small amount (2-3v) of voltage on the ground when code was thrown. With all of that being said, I am at a loss at this point and out of ideas of things to test. Any help is greatly appreciated.

[ErinC]

Anyone?

[RonSSnova]

Explain the voltage on the ground?

[Russ K]

Check for excessive crankshaft end play.

Russ Kemp

[ErinC]

Just checked end play and it is .003 in one direction, so I highly doubt thats the issue. I also inspected the block for evidence of the reluctor touching down when I had it out. As for the voltage on the ground side.....Im still not sure what to make of it. When we were back probing the ecu with a scope we witnessed voltage on the ground when the error occurred.

[RonSSnova]

I modified an Fbody harness for my Nova. So I got more familiar with it than I bargained for. Ha!

The PCM grounds at the back of the drivers side head. There are 2 lugs under the one bolt.
You might check these and make sure no busted wires there.
Also, be sure the engine itself is solidly grounded to the frame. I'm not sure how GM did that in the Fbody. I used a large batt cable from the block.

Good job using an O-scope!

In a 12-14v system, 2-3 v is quite a lot of voltage to lose....

Good luck!

Ron

[RonSSnova]

Did you figure this out?

[ErinC]

Did you figure this out?

No I haven't. I just installed a new ckp sub harness we made with shielded cable, new ecm pins, and a new ckp connector. This sub harness also grounded the ecm and block, which acts as a ground drain for the harness...... no change. I am completely out of ideas.