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2002 Buick LeSabre:
Misfire Condition Occurs only with Engine Load

Alex Steele
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I recently developed a disturbing problem with our car. We have a 2002 Buick LeSabre Limited 3.8-liter with an automatic. Recently we completed a round trip from Dallas to Des Moines and back, and after the last fill-up in Oklahoma the car developed what feels like a misfire condition.


It seems to occur only at an rpm range between 1500 and 2000, at 45 to 50 mph and still in 3rd gear. This occurs only when there is a load on the engine. I can rev the engine in park from 1000 rpm up to 2300 rpm and it runs perfectly smooth. I have run an injector cleaner (Seafoam) in two tanks and there has been no improvement.


Once it's in 4th gear (OD) it smoothes out with no indication that there is anything wrong. At first I thought it was a wheel balance problem, but when you let off the gas the stumble goes away, and coasting at 45-50 mph is smooth. New tires and balancing were done prior to the trip.




The first thing that comes to mind, and what I believe to be the most frequent cause of a misfire, is a failure in the secondary portion of the ignition system. That's the half of the system which actually produces and distributes the spark, including the ignition coils, ignition wires and sparkplugs.


The Buick 3.8-liter V6 uses a distributorless ignition with three two-post ignition coils. A technician may be able to narrow down which cylinder is acting up during a road test with a scan tool, or perhaps even replicate the condition in the shop. Knowing which is the problem cylinder makes diagnosis that much easier.


The coils, wires and plugs should also be visually inspected and resistance tested. Another possible cause of a misfire is the fuel injectors. Aftermarket products added to the fuel tank usually have no effect on injectors that are bad enough to cause symptoms. General Motors recommends a fuel injector test procedure using a special tool which compares fuel pressure drops through each injector. Then you know which ones to replace, and which ones may be saved with a special injector cleaning tool and solvent.


The 3.8-liter has also had a few cases of a hard-to-detect intermittent chuggle on light acceleration, caused by a defective throttle position sensor. It could even be a problem with the lockup torque converter engagement of the transmission. And this is just the top of the list of potential causes, so don't replace anything prior to a definitive diagnosis.


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Buick | Misfires | Ignition
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Earl Eidbo
14 Nov 2011, 14:38
Thanks Larry!
Everything you said was right. I replaced all the parts on the throttle body except the mass air sensor, which I cleaned very carefully. But I was also told that a common problem with that engine was a leaking gasket under the intake plenum. I checked, and sure enough the chamber was full of antifreeze. I replaced the plenum with the new improved version, and the reducer for the return exhaust valve.

I started it up with excitement, only to be disappointed, because it still stalled. I took it to another mechanic. He puzzled over it for a while, and discovered that the catalytic converter had fouled up from all the antifreeze going through it. I'm in the process of replacing the converter.
27 Apr 2011, 08:00
It is common for the throttle valve to cake up with carbon (coking) blocking air flow for the Idle Air Control valve (IAC), remove the air intake tubing form the throttle valve and use a cleaning spray like carburetor cleaner and a rag and clean out the valve, also take out the IAC valve and clean it out also. You may need to replace the IAC valve. The carbon inhibits the IAC to move properly and causes stalling. Check these two suggestions and let us know how you made out.
23 Apr 2011, 19:23
My 2002 Buick Lesabre starts and idles like there is nothing wrong.
It stalls when I step on the gas.
I tested the fuel injection regulator pressure and it read 42 PSI with the key in the on position. I started the engine and it read 42 – 43 PSI at idle.
I pushed on the gas to rev it up, and the pressure went up to 50 PSI, but it was stalling out very badly. I shut it off, and the pressure held very well at the idle pressure of 42 PSI.
Any suggestions? What should the pressures read?


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