Mister MOPAR

Hi, is there any way to clean a heated 02 sensor from a 1997 3.8L Buick LeSabre V6? The car only has 37,000 miles, but occasionally going up a hill in overdrive (going at least 45 mph, but up to 110 mph), the rpm's will rhythmically surge several hundred rpm's. The car also idles a little erratically (it idles smoothly most of the time but the revs jump around every 30 seconds or so, then smooth out)I had a Flowmaster 80 series exhaust on the car, and, thinking that the free flow muffler was confusing my OBD II, I swapped the stock muffler back on. The car will still surge going up hills while in overdrive (especially if I give it enough gas in overdrive to load the motor pretty good, but not enough gas to make it kick down to 3rd). A GM technician told me that a lazy O2 sensor may cause my condition. I know that the O2 sensor is on my rear exhaust manifold. I think there is also a sensor behind the catalytic converter? Could this sensor be at fault too? I'd appreciate anyone's thoughts on why my V6 would be acting up while cruising up hills in overdrive.

Vader

Mr. Mope,

Funny you should mention that the car has "only" 37,000 miles. Bosch recommends changing O2 sensors at 30,000 miles as a preventive maintenance measure. Don't you find it a bit of an paradox that the maker of the sensor advises changing at 30,000 but the warrantor (GM) of the sensor advises CHECKING the sensor only?

In any case, you are correct. There should be sensors at both ends of the cat for diagnosis of its effectiveness. Fuel trim is handled primarily by the front sensor. Unfortunately, as the sensor output degrades, it tends to enrich the mixture rather than lean it out. You may have the exception, however.

The 231s have a history of running very smoothly at idle and very well until something is very wrong. It's such a smooth design that the engine will idle without a detectable miss on five spark plug wires. There is also a history of the ignition coil packs stressing out from the heat and misfiring under load (sound familiar?). Your PCM should catch that and at least set a pending DTC. As a diagnostic measure, you might want to remove the plugs and search for one that may appear different from the rest. If you have a scanner, you can connect and observe the pending DTCs as a guide. If not, you might also want to test the ignition wires and coil secondary resistances. Ususally when a coil dies, you lose two cylinders. That should be noticable under load and would cause the vibration you describe.

Then again, your technician may be right and all you need is an oxygen sensor, but I feel that the "bad O2" diagnosis is the modern knee-jerk reaction to any inexplicable fuel or spark problem, just like the old automated response was "new plugs and carb adjustment". This may be rightly so, since far too many people overlook the 30,000 mile replacement recommendation and many times it may be at least part of the problem's cause.

Just my 2¢

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Later,
Vader
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"Let the bodies hit the floor!"
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Engineboy

OBD2 runs constant system checks on everything that is PCM controlled, it is always comparing the 2 O2s to see if the readings are in range,(FWIW, the rear O2 doesnt do much for driveability..it just lets the PCM know how well the cat is working) I would think if you had a lazy O2 it would set a DTC like Vader said.

Have you tried something as simple as a fuel filter??

If that didnt work I would get into the system and check codes, but on an GM OBD2 system, if there is no light, I would bet there are no codes....

As Vader stated above, I would look at the basics.

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...

R.I.P. #3
"He can see air"

[This message has been edited by Engineboy (edited June 05, 2001).]

Mister MOPAR

Thanks guys! I'm thinking I have a bad coil pack because the shop found a bad plug last week when I had them check the car. The plug had a hot spot on it, the tech said, and he replaced the bad plug (since they're platinum, he didn't do all of them) and he replaced all plug wires. The car had a severe miss when I brought it in due to the bad plug. However, I don't think that the plug was the cause of the problem. I'm thinking that, like you guys suggested, a bad coil is causing a miss on one or two cylinders. I will have the coils checked out. I find it funny that even when the car was missing and popping like crazy when one plug burned, I didn't get a "check engine" light at all. So much for OBDII advanced engine management.

Steven