1993 Pontiac Bonneville Upper intake/throttle body problem

Tiny
CPLEMMONS
  • MEMBER
  • 1993 PONTIAC BONNEVILLE
Engine Performance problem
1993 Pontiac Bonneville 6 cyl Front Wheel Drive Automatic

I recently replaced the plastic upper intake manifold on my Bonneville. I had to do this because I cracked the old one putting it back together after replacing the intake manifold gaskets. When I assembled it with the cracked upper intake it ran fine, but the reason I had to replace it is because it was starting to leak coolant from around the area I cracked. I went to a local junkyard and got an upper intake and throttle body from a 93 Buick Park Avenue (it was a 3.8L and looked identical to the engine in my Pontiac). Everything bolted up just fine, but for some reason the car will not run now and blows a very dense smoke when it tries to start. It's definitely an intake issue, and I've been over the vacuum lines and sensors a hundred times, and everything is connected correctly. I don't have any OBD devices or anything, but I'm thinking it may be a problem with the mass airflow sensor. The MAF sensor on the new throttle body was stamped with different numbers, so I did try the old MAF sensor with it, but it did nothing. When the engine turns over, it sounds as if it is choking and backfiring, but when it fires, it runs up to about 2500-3000 RPM and then shuts down. It's acting as if it's carbureted and someone left the venturi on the back of the carb open. It just fires and dies immediately. If you have any answers for me, I appreciate it! I'm trying to isolate the problem so I don't end up buying a new MAF sensor when it's not really the problem. Spending 140 bucks for no reason would suck. Thanks!

-Chris Plemmons
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Monday, November 16th, 2009 AT 2:33 PM

3 Replies

Tiny
KNOWYOURAUTO
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First, I am assuming you installed a new gasket for the intake and not reused the old one. You probably already know but it can cause a massive vacuum and coolant leaks inside the motor.

The two intakes may be a little different. Although the throttle bodies match up the bolts the coolant passages cross into the air intake and dump antifreeze straight into the motor. I had this problem on a 1992 Bonneville that I ordered but got a 1993 intake. Even though the model years matched for the used car you took the part off, the build dates can be different enough to have an updated part.
Take a close look at the throttle body and the intake when you have it off, you'll probably see they don't match up.

Good luck.
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Wednesday, November 18th, 2009 AT 2:18 AM
Tiny
CPLEMMONS
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I was entirely stumped when the car wouldn't run for even a few seconds. I really had it whittled down to the throttle body as the culprit, I knew when I saw the two different part numbers on the MAF sensor things would get ugly. I'm going to head to a salvage yard maybe this weekend and get a throttle body off of an actual 93 Bonneville. I really thought the main engine components on those GM 3.8s would all be the same for a number of years, but that's definitely not the case! Your solution is excellent, with the thickness and smell of the exhaust when it fires, I'm sure that's what the problem is. Thank you so much for that.
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Wednesday, November 18th, 2009 AT 2:29 PM
Tiny
KNOWYOURAUTO
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Thanks for the update. Couple more notes, with all the coolant that has entered the engine you should do the following to prevent further damage.

1) Remove the spark plugs (all 6), disconnect the fuel injectors and crank the engine over a half dozen times to expel the coolant. Skipping this step can cause the engine to hydro-lock and bend a connecting rod.

2) Change the oil, water doesn't lubricate engines very well.

Your votes would be greatly appreciated.

Good luck.
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Wednesday, November 18th, 2009 AT 2:56 PM

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