1996 Pontiac Bonneville issue - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-24-2009, 05:50 AM   #1
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Angry 1996 Pontiac Bonneville issue

Well as of right now i've owned the car for 72hrs, and for whatever reason i have the worst luck with 3800'*. Earlier today i had a friend patch up a leak in my gas tank, and i figured that was the end to the issues with the car since what i pay'd for it was a steal and for the most part it'* in good condition. Well after doing so i drove home and got right onto my road and the car just up and died about 150ft away from my drive way. Up untill my friend stopped by to help me figure the issue out i was clueless, he pulled the Tb off and found there to be coolant running right from the upper plenum. Earlier while working on the tank i looked through all the fluids and added almost a entire bottle of coolant to the car since there was none in either the radiator or the res.
So we than pulled all the plugs out and cranked it over, coolant shot from every which way and after that we went ahead used my other plugs and re installed the wires and gave it another go. For a min all it was doing is burning off all the coolant and when it came down to it where we poored coolant back into the radiator it ran for a short period of time up untill it eventually died once again.
From what im hearing my friend told me that it'* the UpperPlenum that needs to be replaced, apparently there is a tube that comes up from the lower part of the plenum that has a common issue to go bad. With that being said , and from what i've already posted do i need to replace the plenum along with a new upper plenum gasket? Or is there more major problems that im not seeing?

In the state of Michigan there is a 30day lemon law that id obviouse fall under , i have to get into contact with the dealership tommorow morning and see what there willing to do but id like to see what everyone on here has to say about the issue i've stated above.

Any ideas?

Anything and everything is welcome .. thanks
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Old 07-24-2009, 08:15 AM   #2
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You need to change the gasket. It goes bad around the EGR tube. Hopefully you didn't damage the bearings by running it with coolant in the cylinders. I suggest draining the oil and flushing it out real good when you change the gasket.

EDITED: This post is wrong, please do not rely on it.
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Old 07-24-2009, 08:41 AM   #3
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Sorry for editing your post Dan, it'* a bit incorrect as to the problem.

The problem that occurs is the EGR port in the UIM gets heated by the EGR gasses in the stovepipe that passes through the LIM and UIM to deliver the EGR gasses into the UIM for reburning.

The heat degrades the UIM and causes a weak spot that typically cracks. The coolant supply for the TB is on the other side of this cracked part of the UIM and fills the LIM with coolant until it spills into the cylinders. This has the potential to hydrolock the motor.

When you change the UIM, I would suggest changing the LIM gaskets at the same time if they are black in color. Black means they are the plastic material and not the updated GM dealership aluminum gaskets.
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Old 07-24-2009, 01:51 PM   #4
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How hard is it to change the LIM exactly? Im still awaiting the responce from the dealership because i know that as of now im going to need the plenum with gaskets, along with new plugs and i was going to change the oil as well.. Is there any products that are good to use when i do a flush on the engine?

Anything else i should look for as too going wrong on this whole tare down?

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Old 07-24-2009, 10:40 PM   #5
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The gasket I was referring to was the UIM gasket. Guess I should have stated that more clearly.
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Old 07-24-2009, 11:09 PM   #6
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I understood you Dan
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Old 07-25-2009, 12:58 AM   #7
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To change that manifolds is deffinatly an all saturday job if you have the right tools...and beverages... If you are mechanically enclined, it shouldnt be too hard. i think there is a post in the tech info section on how to do this. i havent really checked... but maybe... anyway... yeah, if you are proficient around an engine, go for it.

Edit! here you go. this should help.

https://www.gmforum.com/t278911/

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Old 07-28-2009, 02:33 PM   #8
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Well we went ahead and replaced the Plenum, and the car runs great now.. Only took about 1hr to pull the plenum off and install the new one .My next issue is why i am getting about 250miles to a tank..... I changed the oil, put new plugs in the car and the wires are in pretty good condition, my next bet would be change the fuel filter, and clean my K&N drop in.. any other ideas?


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Old 07-29-2009, 12:38 AM   #9
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tranny service and keep up on the tire pressure. easy on the pedal.
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Old 07-29-2009, 08:26 AM   #10
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While you were burning coolant there is a good change it fouled out your O2 sensor.

The bank 1 sensor 1 (the one that matters) is in the rear exhaust manifold and can be seen by looking down past the strut tower bar.

Many have had bad luck with Bosch O2 sensors. The suggested brands are AC Delco or Denso. Rockauto usually has a rocking deal on the Denso'* and using the club discount code you save even more.
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