92 Lesabre has no acceleration after 60+ miles of driving.

OptimistPrime

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I've got a problem with my 92 Lesabre that I just can't pin down. The car drives great, perfectly, for about 60 miles. Then it starts to have no acceleration. Step on the pedal and nothing happens. The only way to get it to accelerate is to feather the gas pedal, but even then the problem gets steadily worse, until the car barely drives at all. For example, I recently drove to a town 50 miles away. Car was great on the way. It sat for a couple hours while I performed the work I was contracted to do. Then on the way back, it malfunctioned about half way home. I know it's not a fluke because the car has done this before several times when I drive it that cumulative distance. I had previously thought it was the ignition control module, but I just put two new ones in and it still does the same thing, after 60+ miles. I have made a topic here before and the general consensus was bad ICM. I replaced it and the car seemed to drive better, but what I didn't know then was the distance the car predictably goes before it breaks. I thought I had fixed it, but really I just didn't have a reason to drive the car long enough for it to mess up again. I'm fairly certain the ICM is fine.

I took it to a local shop and they turned me away, saying they don't have time to drive the car enough to get it in the problem state. And that even if they did, it would be too hot to work on. I guess this car's fate rests only in my hands now. It's only got 76k miles on it so I'm keen to find out what's wrong. However someone recently rear ended it, and there's a good chance the insurance company will total it. If I let this thing go to the crusher without knowing what was wrong with it, it will always bother me. I really hope someone here has some insight.

Since most vehicle problems are an issue of fuel, air or spark, I began troubleshooting there. We already know it's getting good spark when I crank it, so I guess my next thing to try will be getting the car to its problem state and then testing spark to see if there's any difference. I have a feeling the spark is a dead end though. It's got new plugs, coils and a new ICM. I even tried a set of MSD coils but they made no difference.

Ruling out spark, we now have air and fuel. I think the air is fine because the filter is clean and the MAF sensor is fairly new. Plus, the car hasn't done any of the stalling it did when the MAF previously went out. Even in the worst of its problem state, it never stalls or acts like it's close to stalling. The guy at the shop who turned me away was pretty sure it was the cat, but I've previously had it tested and it was fine. Perhaps the cat only clogs up when it's super duper hot. Like the honeycomb inside is busted up and flapping around? I heard of that happening on some guy's truck before. A piece would flap down over the exit hole when the cat heated up. Since this car no longer needs emission tests I could just delete the cat. But I'd like to be sure before doing that.

The final possibility is fuel. I only bring it up because the car's problem state seems very similar to how it behaves when I have a low tank of gas and take a tight turn. Then all the gas sloshes to one side and starves the fuel pump for a couple seconds. The car struggles to accelerate. It happens only when I'm nearly out of gas, unlike the other problem which happens even with a full tank. Bad fuel filter maybe? But the car runs flawlessly when it's cranked. No sputtering even in its problem state.

I don't think it's an issue being detected by the computer, because there's no warning lights and the cruise control works fine. When this car previously had a check engine light on from a bad throttle position sensor, the cruise control wouldn't work. The other day when the car was malfunctioning, I tried the cruise control and found it had no problems at all maintaining speed. Transmission seems fine, and even when the car won't accelerate well it still will shift gears fine. Usually the car idles great, even in the problem state. However, sometimes on warm start, it will trundle like a dump truck. That doesn't mean it's about to malfunction, though. I just give it a few revs and it calms down. Bad cam or crank pos sensor perhaps? I wonder if a bad one of those sensors would act up more after being super heated.

Sorry for the long-winded post, but I'm just trying to get down everything I can think of about this problem. If anyone has any ideas I'd love to hear them.
 

MelsRegal

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How often do you let the tank run low enough that turns are effected.
The pump uses the surrounding gasoline to absorb heat, which doesnt happen if the tank is too low and shortens pump life.
 

OptimistPrime

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I may have missed it, but did you change the wires?

Yes, the plug wires are new as well.

How often do you let the tank run low enough that turns are effected.
The pump uses the surrounding gasoline to absorb heat, which doesnt happen if the tank is too low and shortens pump life.

Not very often. It happened today because I'm still unsure if it's getting totaled or not, so I've been hesitant to fill up. It's actually pretty hard to tell how much this car has in it when it gets below a half tank. Now I'm thinking I might put one last tank in it and drive around my city's 60 mile beltline loop until I start having the issue. If it's an easy fix I'll buy the car as salvage and fix its dents myself.
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MelsRegal

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Since you may have a 28 year old fuel pump, that might be another possibility.
 
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My vote is the cat. If it was a fuel issue it wouldn't slowly lose power it would act like it was completely out or start sputtering. Try some full throttle runs after the engine and cat are up to temp and see if it goes through the whole rev range with out bogging down. If it's the cat you'll notice a problem right away. Just cruising would take longer to make the cat act up.
 

Regal LTD Coupe

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I would cut the exhaust pipe just before the cat and take it for a drive.
 

OptimistPrime

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At this point I'm committed to chopping this thing. The car will never be emission tested again, so a cat is just dead weight. This way at least I can recycle it and recoup part of the cost from paying a shop to weld it for me. I can get a fouler cap to cover the O2 sensor so the check engine light stays off. I'll get the pipe welded and take it around my city's beltline loop road, which by amazing coincidence is exactly 60 miles. Of course I'll have to wait until Tuesday to get all this done, because of the holiday. But in the meantime I might take it around and see if I can spot any redness on the cat. I'm not sure if I can get under the car with my sawzall to cut it off myself. It was hard enough making the cut on my S10, and that thing has way more ground clearance.

The guy at my local shop had suggested unscrewing the O2 sensor for more airflow, but I think he was under the impression this this car has a pre-cat sensor, which I do not think it has. Unscrewing the sensor after the cat will do nothing if the cat exhaust outlet is clogged. This is why I prefer to do my own work.

Thanks for all the help, guys. I'm excited to see what this thing runs like without cat restriction.
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The o2 is pre cat not after the cat. Newer cars have four o2 sensors. Two before and two after unless it's a four cylinder. You need to keep the o2 in the system or your engine will not run very well. You lo will have a check engine light and poor performance. Just cut the cat off and replace it with a straight pipe. Remember to do some hard acceleration runs while you're doing your city loop run.
 

Regal LTD Coupe

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If the cat has blown its innards into the muffler and is causing a block, the cat will be hollowed out and be of no more value than its weight in scrap metal. Since it's still running there's a good chance this hasn't fully happened yet. I'm only guessing that's what the problem even is but a good Magnaflow cat and muffler could be sourced and welded in for a few hundred dollars.
 

OptimistPrime

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Okay, think I might have this problem sewed up. I drove the car long enough to get it in the trouble state, then examined the cat. No redness that I could see. I located the O2 sensor but didn't have a big enough wrench to get it off. I think it's like a 23mm? I also couldn't find the fuse for it on the panel. So, I just unplugged the O2 sensor pigtail and left the sensor in place. I went and drove the car about 80 miles. 20 on surface streets and 60 around that loop road. Full throttle the whole way, too. I waited until dark so traffic would be lighter. The car drove great, except for the check engine light being on. Previously the car had driven well for about 30 miles, lousy for 30 miles after that, and then it would finally hit the wall after 60 or so miles. I crossed my fingers that the thing wouldn't crap out on me 30+ miles from home. As I got past the half way point, I pressed the car harder and harder. She ran like a top the whole time.

Is it possible the O2 sensor was the culprit? I've heard of a bad one causing the car to run like crap, but never something like this. Still, 80 miles of driving is the farthest I've had it out without the problem hitting me, so I'm inclined to say something is working right.
 
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Did you check to see if you had any engine codes before you unplugged the o2 sensor?
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I would clear the codes if possible and plug the o2 back up. Then drive it till the check engine light comes on. Then take it to an auto parts store that can scan it for you. That's what I would do to see if the o2 was doing or has gone bad. I bet your gas mileage has suffered quite a bit since this problem started.
 

2007LucerneCXL

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It's a OBD1 so it can't be done by parts store as they can only do OBD2, a service shop or someone who has a OBD1 scanner would be the option.
 
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You can pull the codes off an OBD1 pcm with a paperclip yourself. I just don't remember which pins to cross, but it will flash the code through the check engine light. Maybe someone will remember what pins you need to cross or just Google it.
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OptimistPrime

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I seem to remember having this O2 sensor replaced at one point. It's not OEM. I had to have like $900 bucks worth of work done to the car for it to pass its very last emission test, and the sensor was one of the things they changed.

I would clear the codes if possible and plug the o2 back up. Then drive it till the check engine light comes on. Then take it to an auto parts store that can scan it for you. That's what I would do to see if the o2 was doing or has gone bad. I bet your gas mileage has suffered quite a bit since this problem started.

Thing is, the light hardly ever comes on with the sensor plugged in. Even with the car totally messed up and not accelerating it has no light. Maybe once every few weeks I've spotted it come on for a second, but then it's gone again. Part store scanners can't diagnose it since it's an OBDI car. And yes, it's gotten lousy mileage for a while now.

You can pull the codes off an OBD1 pcm with a paperclip yourself. I just don't remember which pins to cross, but it will flash the code through the check engine light. Maybe someone will remember what pins you need to cross or just Google it.

Oh right. I forgot about that. I'll have to google it. I think it's the farthest on each side that need to be shorted. But I have no idea how to translate what the flashing means. Maybe there's a listing somewhere online.
 

OptimistPrime

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The parts company sent the wrong O2 sensor, so I'm still waiting on the new one, but I'm confident to have found the issue. Now my biggest problem is that the lousy shop I took this car to all those years ago that changed the sensor apparently cross-threaded the thing and torqued it down with an air gun. Half the threads were stripped. Now I'm worried this the sensor won't stay torqued.

While I worry over that, and wait for the part to arrive, I spliced a switch into the O2 sensor circuit, so I can turn it on and off at will. I went to the junkyard and cut the O2 sensor pigtail out of a dead Lesabre. Each side of that pigtail runs to a corresponding side of a switch under the dash. Then I plugged this in between the existing O2 sensor wire and the car's O2 sensor pigtail. So I have this working without having to cut my car's original wiring.
 
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So what's it do when you switch it off and on? Does it make a difference?

If the threads are stripped just weld it in. Jk.😁 If you have a tap I would chase the threads and clean them up.
 

OptimistPrime

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So what's it do when you switch it off and on? Does it make a difference?

If the threads are stripped just weld it in. Jk.😁 If you have a tap I would chase the threads and clean them up.

With the sensor on, the car runs pretty much like it's been running for the better part of two years. Sluggish and poor gas mileage. I assume if I drove it far enough it would have the acceleration issue as well. With the sensor off, I get more power and better mileage, though the service engine soon light is on constantly after a few miles. Haven't had a problem with acceleration yet, and I've driven it a couple hundred miles like this.
 
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