96-00 Vortec Problem

Degnol · 06-20-09, 05:37 AM

135,000 miles, well maintained as in I've owned it since new. Started bucking on startup, intermittent at first, now more consistently. Put on a new starter, same thing. I suspected head gasket but pulled plugs and there is no coolant in the cylinders at all. Small coolant leak at the back of the intake, but no coolant in the oil at all. I'm beginning to think it is one of the "sensors" but have no idea where to look. BTW, it throws no codes

But if the knock sensor was whacked, could the ECU be advancing the timing to the point where it would buck?
Once it starts, it runs just fine, makes good power and generally acts normally.

Am I condemned to take it to the GM dealer?????

lingo · 06-20-09, 09:08 AM

Check the timing to make sure that it is correct. The base timing should be set at 0 degrees.

Degnol · 06-20-09, 09:11 AM

Thanks Mike. I talked to a GM tech and he said it may be the CKP (crankshaft position sensor). That would affect timing. It bucks just like when you install a new tach and get the timing too advanced.

Ed

Degnol · 06-20-09, 11:03 AM

I replaced the CKP and had a little problem....the last step in the installation is to "Perform the CKP Variation Learn Proceedure" which requires a "Dealer-level" scanner

However there is no harm in starting and running without performing that as the engine has to be running and warm when it is done. So, I started it and no bucking! 'Course the problem was intermittent, so

FineWynsFJ40 · 06-20-09, 03:41 PM

Some trouble codes won't light up the Check Engine Light, so you have to check it regardless of whether the light is on or not. The computer system teaches itself as it drives, so it should be good. The computer can figure out for itself what to do, and doesn't need you to adjust the distributor cap for it

Good luck!

Degnol · 06-20-09, 04:30 PM

So, are you thinking I don't need to go to the dealer and have the "Learning" proceedure done....that is if this fixes it? That would be cool

I gave the distributor cap three coats of Carnuba wax

so I should be good there.

Thanks,

Ed

Degnol · 06-22-09, 05:00 PM

On the advice of a mechanic buddy I replaced the distributor cap and rotor and VOILA! Starts(repeatedly) and runs fine. My buddy said to use only AC Delco or Borg Warner. I had it replaced at 98,000 miles, but I do not know what mfr they used. I think those flat caps have a tendency to short out inside. Anyway.....fixed.

Thanks!

Ed

Elbert · 07-05-09, 12:15 AM

FYI... you don't have to go to the dealer for the "learn process" most new scanners have the ablity to check the camshaft offset angle...

On the new engines you don't set the timing per say... The ECM controls the entire process, you do have to get the camshafte offset angle correct or close _+2 degrees. which you do my having the engine running as I recall at 1K RPM and monitor the offset angle with a scan tool , you move the distributor left or right to get it set right...which I think is 0 degrees. By the way its a challenget to get the dist set correct as almost any movement will change it by 5 or 8 degrees too much.