1995 Buick Lesabre engine stumbling

Tiny
DPLEMEL
  • MEMBER
  • 1995 BUICK LESABRE
  • 3.8L
  • V6
  • FWD
  • AUTOMATIC
  • 160,000 MILES
Engine stumbles on acceleration. Runs good on full acceleration @higher rpm. Engine light code is icm trouble. Replaced icm, coils, wires, plugs, fuel filter, throttle position module, cleaned maf, checked fuel pressure. What is left when nothing has helped.
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Monday, March 23rd, 2015 AT 6:58 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
Have the charging system professionally load-tested. In particular, if all you can get is one third of the generator's rated current, and "ripple" voltage is very high, the generator has a bad diode. That is caused by the generator's design, but the battery helps to overcome that. To reduce the high number of repeat generator failures on '87 and newer GM products, replace the battery at the same time as you replace the generator unless it is less than about two years old.

By now you've figured out throwing parts at a problem is the most expensive and least effective way to diagnose a problem. On GM vehicles, the generators develop huge voltage spikes that can damage the internal diodes, the voltage regulator, and can interfere with computer sensor signals. The generator is the most common cause of intermittent, elusive engine running problems that defy diagnosis. Start with a fully-charged battery, disconnect the small plug from the rear / side of the generator, then drive the car. If the problem has cleared up, replace the generator and battery.
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Monday, March 23rd, 2015 AT 8:26 PM
Tiny
DPLEMEL
  • MEMBER
That didn't help. Still stumbles on partial acceleration.
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Wednesday, March 25th, 2015 AT 6:32 PM
Tiny
CARADIODOC
  • EXPERT
What didn't work? I listed a few different things. Tell me exactly what was done and the results of any tests. I like numbers to work with if possible, not just opinions.

I just had another unhappy car owner today who I told to replace the battery two weeks ago. He's mad because his new generator failed and needs to be replaced again. When I looked under the hood, I saw the battery was full of corrosion, the typical sign the battery is near five years old and is going to die a normal death within the next six months. After a lot of persuading, he finally put in a different battery, and even with the failed generator, his running problem cleared up.
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Wednesday, March 25th, 2015 AT 7:46 PM

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