1992 Buick Lesabre mystery intermittent rev problem happens

Tiny
FACELVEGA
  • MEMBER
  • 1992 BUICK LESABRE
Engine Mechanical problem
1992 Buick Lesabre 6 cyl Front Wheel Drive Automatic 99k miles

My 92 LeSabre (3800 V6) is in generally excellent condition, running well and getting very good fuel economy (27mpg highway), but has developed a problem similar to one I've seen posted in various forums, but never really answered: when the engine gets unusually hot for fifteen minutes or more and reads a tick or two higher on the temperature gauge for a while (typically in stop-and-go traffic, after a jam, or on a long steep hill-- but on a long highway drive it never happens), it will suddenly not rev above a certain level, usually either around 2800 or 2000rpm, but one or the other, not fluctuating during an episode.

When the engine tries to rev above this, it cuts out as if it's getting no fuel, but then recovers immmediately. Pressed very hard, it hesitates badly and once even stalled, though it started right back up in neutral. The problem persists even if you stop and restart the engine, but resets if I let the car cool for fifteen minutes before restarting. Occasionally after this has been happening the car will not restart at all for about 15 minutes, though this may be an unrelated problem. Normally the starter and battery work fine. But without being stopped and cooled, the car will continue to do this indefinitely, even if it gets a long stretch of highway and cools back down to normal operating temperature.

No codes the two times I've checked, though haven't checked recently and the problem is getting worse, either over time or in the summer heat. I've had the crank sensor replaced since this started, but it seems only to have cleared up a possibly unrelated problem of intermittent stalling from a stop light. New plugs, wires, coils, alternator, and water pump since the problem started as well. Fuel pressure is good (though never tested when the problem occurs) and filter is clean.

Next step? ECM? MAF sensor? Potential EGR or vacuum issue I haven't noticed, or a fuel pump problem (but then why is it so intermittent, and why have others with similar complaints not fixed them with an expensive fuel pump replacement)? It seems to me it must be a sensor/computer issue since the car runs so well otherwise. Throttle position sensor? I'm stumped.

many thanks for any advice!
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Friday, July 31st, 2009 AT 1:37 PM

4 Replies

Tiny
JACK42
  • MEMBER
Could be something in the ignition breaking down when it gets to a certain temp. Those had issues with crank angle sensors (usually no-start situation) and ignition modules, coils. Temp usually wont change fuel pressure, but using a manual gauge will verify if it is good. When it wont start after doing this, does the engine turn over and not start or not even turn over? That is when you will find out the problem if it turns/wont start. Check for spark and injector pulse. Has the check engine light ever come on when itis doing this?
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Tuesday, August 11th, 2009 AT 7:57 AM
Tiny
FACELVEGA
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When the engine won't start for 15-20 minutes after the rev problem happens--which is so far three times out of dozens of incidents--it doesn't turn over at all, as if the security system has cut it off. Everything always goes back to normal when the car cools down, though. The check engine light does not come on.

So since I've changed the coils and the crank position sensor and the fuel pressure seems to be fine, would you say the ignition module is my best bet for a next move? Or should I also re-check that crank sensor and its connections?
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Tuesday, August 11th, 2009 AT 11:27 AM
Tiny
JACK42
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Could very well be the module, but it is an expensive try. Last I saw they were pricey. The anti-theft on that car should only shut down the fuel pump, not the starter circuit. Have you checked to see if it has 12 volts at the small wire on the starter when it wont crank over? If nothing, check at the ignition switch for good power in and out when in crank position
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Tuesday, August 11th, 2009 AT 12:45 PM
Tiny
FACELVEGA
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Many thanks, Jack! I don't think it's the security system, but I do think it's electrical and not fuel related (Of course, I want to think that with needing to drop the tank to get at a lesabre fuel pump). I see some new old stock modules online for a reasonable $50, but I'll check the voltage at the starter wire first. Wish I'd thought to change it when my brother swapped out the coils and plug wires.

The not starting isn't much of a problem for me, it's the intermittent unwillingness to rev. I'm in central NYC, so when she suddenly won't do 2000rpm while I'm climbing a busy bridge or in the middle of the Holland Tunnel it's a real issue, and the traffic jams here mean that the problem gets triggered ten times more often than it would if I was out in the country or suburbs.

Thanks again!
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Tuesday, August 11th, 2009 AT 4:23 PM

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