Pontiac Grand Prix

1999 Grand Prix GT not a S.C. 106,000 miles. Just replaced upper intake Plenum with gaskets and new PCV plus cleaned throttle body and replaced bad MAF sensor. Now car starts rough and sends a white plum of smoke right after ignition but that quickly goes away. Car is noe losing a lot of oil somewhere and there are no apparent leaks. There is a sucking air sound coming from EGR that I have never noticed before. Is this air leak from the EGR the cause of my oil loss? Also, OBDII scanner reports bad Knock Sensor. Could this the problem and where is the knock sensor located? My Chiltons doesn't even list it.

Thanks !
June 21, 2007.

Should have done the lower intake gasket at the same time, real common for leaks of both coolant, air and oil; with any combination there of. That is probably the white smoke issue and oil loss.

Do you mean the gasket between the Upper Plenum and Lower Intake or below the lower and if below the lower why all of the sudden the oil loss? The lower mainfold wasn't even touched.

Jun 21, 2007.
I'll update this when I can, and see if I can help better. The intake gasket is the lower one below the manifold, not between the plenum and manifold. I am assuming this is the 3.4 motor?

This may not be the problem, but would be a huge concern if it were mine and if it is the 3.4.

If you changed the vacuum in the motor from the work you did and made it better, a border line intake gasket can get pushed over the edge. I probably jumped the gun. Especially since there are no misfire codes.

Sorry, I have a 3.8 in the car. I understand what you are saying now about the gasket now.

Jun 21, 2007.

Hey I'll tell you one thing about those 3.8 motors is the plastic manifold goes bad. The coolant cuts a groove into it from poor engineering, and it can rapidly fill up a cylinder causing hydrolic lock and twisting the crank/piston etc.

I think I'd pull the egr off if needbe to investigate the sucking sound. Wonder if carbon got loosened up and is trapped in the egr? vacuum at the egr? Not sure on that, but would have expected a code. The code for the knock sensor may not mean it's bad. Her's the location anyways.

Paul, thank you for the knock sensor pic, it helps a lot. The coolant leak is the whole reason I changed the upper plenum, although I never had the serious problem I didn't want to take any chances but know it seems I've made things worse, the smoke and eating oil. Thanks for all of the advice and I will keep you posted on what I find. What do you think of the Tomco Kleen Screen EGR gasket Kit? Think it works?

Thanks again,


Jun 22, 2007.
Yes I like it, yes it works.