92 Lesabre no acceleration when hot

OptimistPrime

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I just got done limping my Lesabre home through heavy traffic. It couldn't go faster than about 50 mph. Over the last week or so I had noticed a drop in power once the car heats up, and today the problem seems to have come to a head. I spend a LOT of time in traffic. Today's trip was about 30 miles and it was bumper to bumper most of those miles.

So now I'm trying to troubleshoot. I don't have a check engine light coming on, which make me think I can rule out the MAF and TPS. The car also hasn't stalled once, which was indicative of failure in both those parts. Vehicle has 67k original miles on it. Trans has been serviced recently, and it seems to shift fine. I'm suspicious that the catalytic converter might have failed. I haven't experienced many failures of those, so I'm not sure if heat effects the performance. I'm also suspicious of the crank position sensors, but as I stated the car hasn't stalled once, despite what seems to be a bad problem with airflow.

Is there anything I'm missing in my diagnosis? My state doesn't test emissions on cars as old as mine, so I might just cut that cat out and staightpipe it. Has anyone had success with a cat delete on one of these series 1 3800 motors?
 

2007LucerneCXL

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Age and not milage may be considered on service parts. Not knowing what has been replaced, if ever, could be the source. The cat would probably not be a issue as it would be a problem hot or cold in most cases.

Temp sensor, spark plug wires, thermostat, fuel filter or pump, ICM coils, it's a list that could be many items that may have already been taken care of. Could be a stored code, but you would a shop or a older reader.
 

OptimistPrime

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It has new plug wires and plugs. It hasn't had any problems starting, so I doubt it's the fuel pump. It doesn't seem to be losing spark or misfiring. I have no idea where the temp sensor is located on a series 1 engine, though I might be able to find the thermostat. Without a real temp gauge it's hard to tell if it's running hot.

Lately the idle has been a bit rough, especially if the car sits at a light for a minute or two. Doesn't always happen though.
 

2007LucerneCXL

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2007 Lucerne CXL. and 1995 Lesabre currently, past 1973 Riviera, 1968 Riviera
It's just going off the description of after it's warmed up and looking at items that may be affected. With no CEL or codes it's kind of in the dark, on a Series 1 only one temperature sensor so if it's not operating correctly, sensor or connections, it's not sending the right information to the ECM once it's warmed up and fuel/air is not correct. ICM and coils can also have issues once warmed up, wiring harnesses can also be subject to change when warmed up.

Sorry wish there was a simple fix, but it's a little hard on trying to pinpoint from this side of screen at times. Hopefully others on the forum may have suggestions to help out.
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OptimistPrime

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This car is so hard to work on not having those codes. I just can't take it to any shop around where I live. There's not a reputable place within 20 miles, and I've tried them all. There's a reason I do all my own car repair.

At this point I have a few questions. Forgive my ignorance for I am a novice.

1. Is there any picture anywhere on the internet of where on the motor the temp sensor lives? Because I have searched up and down Google and came up empty. Looooots of info on the series II motor though. Not that it helps me.

2. Is there a way to test the ICM and coils? I assume using a voltmeter, but what exactly to look for?

3. Could the temp sensor affect mpg? I seem to have noticed a bit of a drop, though I can't say for sure. It seemed to eat up a lot of gas today. I just had the temp sensor on my truck go out, and it cut my mileage in half when it wasn't working right.

I'm going to let it sit overnight and see how it drives. If I can find where the temp sensor is, I'll probably swap it out, since it's like a $15 part.
 

HotZ28

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This car is so hard to work on not having those codes. I just can't take it to any shop around where I live. There's not a reputable place within 20 miles, and I've tried them all. There's a reason I do all my own car repair.

At this point I have a few questions. Forgive my ignorance for I am a novice.

1. Is there any picture anywhere on the internet of where on the motor the temp sensor lives? Because I have searched up and down Google and came up empty. Looooots of info on the series II motor though. Not that it helps me.

2. Is there a way to test the ICM and coils? I assume using a voltmeter, but what exactly to look for?

3. Could the temp sensor affect mpg? I seem to have noticed a bit of a drop, though I can't say for sure. It seemed to eat up a lot of gas today. I just had the temp sensor on my truck go out, and it cut my mileage in half when it wasn't working right.

I'm going to let it sit overnight and see how it drives. If I can find where the temp sensor is, I'll probably swap it out, since it's like a $15 part.
#1. There are two temp sensor on the Series I, one located below the T/B in the LIM which is a 2-wire sensor that provides info for the ECM/PCM, and the other one is an 1-wire located on the back side of the drivers side LIM which provides info for the gauge/light.
#2. The ICM can be tested at most auto part stores. The coils can be tested with DVM ohm readings, but the best test is with a spark tester. I don't think that is the problem!
#3. The temp sensor can effect gas mileage if detecting a cold engine, after the car has warmed up, but I think you may be on the right track with the plugged cat! Have the back pressure checked and if above 2.5-psig, gut it, or cut it out!
 
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GliderRides

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One minute with a vacuum gauge will show if the cat is clogged.

Temp sensor can be checked with an ohm meter. Symptoms do point in that direction.

New plug wires are never a guarantee, I've had some dead wires right out of the box.
 

LARRY70GS

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One minute with a vacuum gauge will show if the cat is clogged.

Temp sensor can be checked with an ohm meter. Symptoms do point in that direction.

New plug wires are never a guarantee, I've had some dead wires right out of the box.

X2 on the vacuum gauge. Fully warmed up in Park, it should make an easy 20". Open the throttle to maintain 1500 RPM and watch the gauge. It should stay at 20" and not drop off. If it does, that indicates an exhaust restriction and the cat is the #1 suspect.

Lots of electrical components fail with heat. If you were getting misfires, I'd say plugs, wires, coils, but it doesn't sound that way. I'd check fuel pressure when hot, but again, if that was a problem, it would misfire.
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OptimistPrime

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I am going to get the cat tested at first opportunity. But, I drove the car around today and it worked fine. No problems accelerating or running rough. I'm starting to think it's the temp sensor under the TB. The engine was operating at unusual stress yesterday being stuck in that traffic jam. Perhaps the coolant became superheated due to the bad sensor. The car immediately drove better yesterday after giving it a short (five minute) rest with the hood up.
 

Homer Jay

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Whatever it's worth many years ago I had the identical symptoms with a 92 Bonneville. As suggested earlier, replacing my ICM solved the issues.
 

OptimistPrime

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I'll probably give that a shot if the problem persists after I swap the CTS. The fact that I was able to drive it for a number of miles today without the issue happening concerns me. This is the kind of problem that got me into working on my cars, because you know it would be big money to diagnose such a phantom condition at a shop. I had a place keep this car a whole month trying to diagnose one issue in particular. I said no more after that misadventure.
 

OptimistPrime

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I got the CTS swapped. Now to road test and see if it messes up again. I'm concerned about not being able to reproduce the conditions of that last drive without it being a lot hotter outside than it is.
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