1999 Pontiac Bonneville Acts like bad gas?

Tiny
CHEVELLEMAN
  • MEMBER
  • 1999 PONTIAC BONNEVILLE
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 108,000 MILES
I have a '99 Bonneville with 108K. The car at times, espicially when first starting out acts like it has bad gas and has no power and seems like it is missing. It isn't bad gas, because it has done it every tank for a long time. The gas mileage on the car is also dropping.I am down to 16mpg in town. I think it also might be going through some antifreeze, as that is what is smells like at times. I have had the plenum (?) On it replaced a couple of years ago because it was going through antifreeze. I was told that I should also have a backpressure test done to see if the catalytic converter is plugged. Any suggestions?
Thursday, November 6th, 2008 AT 10:16 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
It could be several things. It could be an intake problem, cat conv problem, O2 sensor, and a list of other things.

To get started, I would suggest having the computer scanned for trouble codes. Hopefully there is a code saved by the computer that will tell us exactly what is going on.

How much coolant are you loosing? Also, as far as having it scanned, find a nationally recognized parts store and have it done there. Most of them will do it for free.

Let me know what you find.

Joe
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Friday, November 7th, 2008 AT 9:19 PM
Tiny
CHEVELLEMAN
  • MEMBER
  • 4 POSTS
Joe, I couldn't PM you because I don't have 10 posts yet.

The code that came up on the car is a P1811 MAX, adaptive long shift strategies code.
The mechanic basically said that it is like it is staying in 2nd sometimes and that is what is causing it to act like "bad gas".
He recommended two different solutions. Do a complete transmission service, with some good conditioner at about $250 for the service, or replace the Pressure Control Celenoid at around $800.

I don't want to stick a bunch of money into the car, quite frankly because it probably isn't worth it. It is a nice car, and had been a great car, but we are probably going to sell it anyways.

What do you think?

Thanks
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Monday, November 10th, 2008 AT 4:56 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi:
I don't know where you live, but the prices sound really high to me. Yes this could be the problem. If you plan to trade the car, I don't think I would put the money into it. You'll be over a grand and praying it fixes the problem. It's hard to believe that a 1999 is almost 10 years old, so I checked Kelly Blue Book for you to see if the car's value is worth the investment. I found the following trade-in values based on the car's condition:

Excellent
$1,925

Good
$1,625

Fair
$1,125

I wouldn't put the money in it if you plan to get rid of it; however, if you plan to keep it, that is another story.

If you want to check out used car pricing, go to:

KBB. Com

I hope this helps. Let me know if you have any other questions.

Joe
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Monday, November 10th, 2008 AT 5:05 PM
Tiny
CHEVELLEMAN
  • MEMBER
  • 4 POSTS
Ya, I don't think that I am going to put the money into the celenoid, but I think I am going to have the transmission serviced. Do you know the process of replacing the celenoid. Just out of curiosity, is it a hard replacement?

I am not going to trade the car in anyways, I will try and sell it outright.

I thought that the price to repair the pressure control celenoid did seem high. Maybe the service will help out.

Thanks for the response to the question. I really appreciate it.
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Monday, November 10th, 2008 AT 5:24 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi:
To replace the solenoid you will need to get into the trans. I do recommend having a mechanic do it. However, I also recommend a second opinion due to price. Although I feel he is most likely correct, I can't see having to pay more than $400.00 for the repair.

Also, I did a little research for you. I found this is a common problem and the solenoid has been redesigned. Also, here are some other things that could cause the problem:

Sediment inside the pressure control (PC) solenoid valve, causing the PC solenoid valve to mechanically bind.

Sediment in the valve body, causing the torque signal regulator valve to stick.

Incorrect transaxle oil level.

If you have the trans powerflushed, it may help. In the Pittsburgh area the average cost would be around $100.00

I hope this helps you. If you have any other questions, let me know.

Joe
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Monday, November 10th, 2008 AT 5:52 PM

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