1993 Pontiac Bonneville Car runs bad in high temps

Tiny
BCRAIGH
  • MEMBER
  • 1993 PONTIAC BONNEVILLE
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 178,000 MILES
I have a 93 Bonneville 3.8 that seems to run ok when the weather was cold. As the weather gets hotter, or if I'm in rush hour traffic for an extended time on a cooler day, the car seems to run as if it is out of gas. On a hot day, like yesterday when it was in the upper 90's, the only way I can drive the car is by barely touching the gas pedal. If I press the pedal very hard the car falls on it's face and will eventually gets to where I cannot go over 20 miles per hour and the car has no power to pull up a hill. It will also sometimes quit if I come to a stop. I can turn the car off and wait 5 minutes and the car will start back and be somewhat driveable for another mile or two.

I have changed a dozen or so fuel filters, checked the fuel pressure (40 pounds no running and 36 when idle, and goes to 40 when pressing the gas), changed the mass airflow sensor, cleaned the throttle body intake, changed the thermostat, and the air temperature sensor. I also had the exhaust checked to see if the cat was stopped up and it was fine.

Any help with this problem will be thoroughly appreciated!
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Wednesday, June 25th, 2008 AT 11:21 AM

13 Replies

Tiny
DOCFIXIT
  • EXPERT
Has the ECM been checked for trouble codes? If not have it done, if you have what where they?
Let me know
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Wednesday, June 25th, 2008 AT 11:43 AM
Tiny
BCRAIGH
  • MEMBER
The only time the check engine light has come on is when I was on the highway for 3-4 hours, and after trying to limp to the next exit the check engine light will come on. After shutting the car off the check engine light is gone. I purchased an inexpensive code scanner and no codes were displayed. The check engine light normally does not come on. But to answer the question directly, I have not had the car checked for codes by a garage with a better diagnostic machine.
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Wednesday, June 25th, 2008 AT 11:48 AM
Tiny
DOCFIXIT
  • EXPERT
O.K. So you get a light when it goes haywire but it sets no hard code you can retreve later. Lets hook up you coder leave it hooked go drive if she goes see if a code is caught.
Let me know we will get this baby fixed
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Wednesday, June 25th, 2008 AT 11:53 AM
Tiny
BCRAIGH
  • MEMBER
Well, that has been a bit of a problem to duplicate. The only time the light has come on is when I've been on the road for 3-4 hours straight, and still it doesn't come on until it's very dangerous for me to be on the road (going 25 mph on the interstate). The light has not been on for several months just because I'm afraid to go on any trips in the car.

I was just thinking of looking at all 6 spark plugs to see if there was anything obvious in the color. The car has 178k miles and has original coils and most everything else. I did do a tune up (plugs, wires and air filter) about 1 1/2 - 2 years ago. The air filter is new now.
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Wednesday, June 25th, 2008 AT 12:00 PM
Tiny
BCRAIGH
  • MEMBER
Actually, right this minute I can drive the car and it seems ok other than being just a tad sluggish as long as I only push the pedal 1/3. As soon as I push harder than that it falls on it's face.

By the way, in case I didn't mention it earlier, I have also replaced all of the vaccuum lines that I can find.
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Wednesday, June 25th, 2008 AT 12:02 PM
Tiny
DOCFIXIT
  • EXPERT
Being that this is temp related and the fact that weak coils often do not work when they get hot and driving long distance really heats them up and yours are OEM that might be the thing to replace.
Do you agree let me know what happens
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Wednesday, June 25th, 2008 AT 12:07 PM
Tiny
BCRAIGH
  • MEMBER
I will definitely let you know. I've been thinking about the coils for a while but I've just spent a lot of money already guessing. The last car I had that had coil problems missed all of the time and this car just doesn't do that. Either way, I will go out and get 3 new coils within the next hour and try that.

I do have another problem or two with this car that I'll log another question with later.
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Wednesday, June 25th, 2008 AT 12:12 PM
Tiny
BCRAIGH
  • MEMBER
New coils, wires and plugs. That didn't seem to help.
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Wednesday, June 25th, 2008 AT 3:36 PM
Tiny
BCRAIGH
  • MEMBER
I think I have this one licked. I spent the day doing new plugs, wires, coils, cleaning throttle body and all sensors, EGR, and a number of other things. Nothing helped. I finally just went for a drive to get the see how far down I had to press the accelerator to get it to duplicate the problem, then came straight home to put my fuel pressure guage on it. It read 40 pounds like before and 36 when at idle. When I pushed the throttle 1/3 it read a steady 40 pounds but when I gave it full throttle the gauge went to 20 and fluctuated between 15 and 20 or so. I think the fuel pump needs to be replaced, which was my first diagnosis a year ago. I just didn't do it then because I was guessing at it and the fuel pump is an expensive and not so easy to replace part. I will probably do tomorrow (I'm tired of working on this thing). Does this sound reasonable?
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Wednesday, June 25th, 2008 AT 10:00 PM
Tiny
DOCFIXIT
  • EXPERT
Yes fuel pressure should not fall. Pump presure and delivery seemed good at idle but by taking it up in RPMS you proved it can not deliver enough fuel.
It must have been intermittent for the last year and now decided to lay down.
Great detective work
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Thursday, June 26th, 2008 AT 7:50 AM
Tiny
BCRAIGH
  • MEMBER
I got the fuel pump replaced a few days ago (after getting the wrong one the first trip to the parts store) and now the car runs great. All of the other parts I replaced must have help because I'm getting 31 mpg with my first tank of gas on the highway and 26 in rush hour traffic. And when I push the accelerator the car takes off and keeps going like I thought it should. Thanks for your help.
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Tuesday, July 1st, 2008 AT 7:58 PM
Tiny
BMRFIXIT
  • EXPERT
Fuel pressure should be 41 - 47 psi
if not check fuel filter , pulser and fuel pump
fuel tank need to removed for the pump and pulser
good luck

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Tuesday, July 1st, 2008 AT 8:17 PM
Tiny
DOCFIXIT
  • EXPERT
Glad to hear your good results and not giving up. Sometimes mechanical things defy logic.
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Wednesday, July 2nd, 2008 AT 7:42 AM

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