1992 Lesabre - after driving for 8-10 minutes, starts to stall. Engine jumps on highway

[watertree]

Hey, my car has been acting up for a while now and two mechanics haven't been able to fix it. I am hoping for some insight here. The car is a 1992 Lesabre Limited Edition 3.8L v6 engine. It was well taken car of for 20 years, including a brand new transmission with less than 10k KM on it. it has about 150k KM in total on the vehicle.

Here are the symptoms:

1) oil gauge starts to go crazy after driving for a few minutes and the engine has warmed up (touching the accelerator makes it go to max). Someone suggested this might just be a faulty sensor.
2) After driving for about 10 minutes, the car will have small erratic spikes in RPM and possibly what feels like misfires. Sometimes when slowing down, the car stalls.
3) when driving on the highway at high speeds, occasionally, the car feels like the front end jumps (maybe misfire?)
4) check engine light is on. The machine read faulty crankshaft sensor and air intake sensor. It also gave a code for the timing chain. I have replaced the crankshaft sensor and the problem persists.

Both mechanics and everyone I talk to do not believe it is the timing chain and that it is something else but it is getting costly to find. If there's any suggestions I would certainly like to hear them.

 

[TerryP]

What codes is it throwing? You need that before anyone can give you a 'good' answer!
Here are a couple pages that I found with how to retrieve it at home and a page of codes.
Come back and let us know the codes.

How to read older GM OBD diagnostic codes for free
GM Trouble Codes - 2 digit codes
GM OBD 1 Trouble Codes

 

[SAYBER]

What codes is it throwing? You need that before anyone can give you a 'good' answer!
Here are a couple pages that I found with how to retrieve it at home and a page of codes.
Come back and let us know the codes.

How to read older GM OBD diagnostic codes for free
GM Trouble Codes - 2 digit codes
GM OBD 1 Trouble Codes

Yup! Scan it DIFFENITLY! Guessing and just throwing parts at it will get costly. A faulty o.p.s. Will not cause the issues your describing....

 

[BuickGirlFromMars]

I had a faulty computer in a 1990 that caused me to have codes for various unrelated issues. So you definitely want diagnostics. What do the codes say? Then check the codes. If air intake sensor is bad, check its voltage while car is key on. if it varies with temp(and if you can find its spec, even better) then you know its not receiving it, or the computer has issues. Etc. So definitely start with codes

 

[watertree]

Sorry for taking so long, had to track down the old report. It was scanned before doing repairs. It was suggested by the mechanic who performed the diagnostic that it was a bad crank position sensor (huge amount of work, super cheap part) and I replaced that and the old one had a crack in it. But the problem still persists. He also said it could possibly be the PCM.

The codes are:
12 and 34

 

[MelsRegal]

Code 12 is a normal code indicating communication
Code 34 is a MAP sensor code.
Why are they telling you timing chain, is there a rattle from the front of the engine?
Does the shop have ASE certified technicians?

 

[BuickGirlFromMars]

They likely used a universal code source. codes were make-dependent although they followed a general rule of thumb, a buick code 43 and a olds code 43 of 1989, for example, could be two different things.

It means you have low resistance in your MAP sensor. which iirc, means you have very little manifold vaccuum.

you know what that means?

Vacuum leaks. These things on these older cars HAUNT you.

I chased many on my 1990.

SO you know, a vacc leak can be almost not present at start but once you warm up, and the engine heat makes things expand, move, etc, it could be moving something open that then pulls air or it could be just thinning your A/F ratio with Oxygen sensor data that then is unreliably affected by your vacc leak periodically giving too much unmetered air.

Remember, your MAF sensor and your oxygen sensor on obd1 are the only things adjusting A/F assuming your MAP is constant and your atmospheric pressure is constant. Your MAP isnt constant, generally, because wide open has no vacc but idle should have lots. BUt if you are say, part throttle and you have no vacc, then things get weird. Your computer cant sadly account for unmetered air of varying amounts nor could a carb.

FIRST, confirm no engine vacc leaks.
SECOND, make yourself a nice picture albulmb of their locations after finished and how to get to them.
THIRD, start car and run like you have, if you notice its better, its prob better.

There is a slight chance this is your MAP sensor being bad, but i dont think it is.

 

[SAYBER]

They likely used a universal code source. codes were make-dependent although they followed a general rule of thumb, a buick code 43 and a olds code 43 of 1989, for example, could be two different things.

It means you have low resistance in your MAP sensor. which iirc, means you have very little manifold vaccuum.

you know what that means?

Vacuum leaks. These things on these older cars HAUNT you.

I chased many on my 1990.

SO you know, a vacc leak can be almost not present at start but once you warm up, and the engine heat makes things expand, move, etc, it could be moving something open that then pulls air or it could be just thinning your A/F ratio with Oxygen sensor data that then is unreliably affected by your vacc leak periodically giving too much unmetered air.

Remember, your MAF sensor and your oxygen sensor on obd1 are the only things adjusting A/F assuming your MAP is constant and your atmospheric pressure is constant. Your MAP isnt constant, generally, because wide open has no vacc but idle should have lots. BUt if you are say, part throttle and you have no vacc, then things get weird. Your computer cant sadly account for unmetered air of varying amounts nor could a carb.

FIRST, confirm no engine vacc leaks.
SECOND, make yourself a nice picture albulmb of their locations after finished and how to get to them.
THIRD, start car and run like you have, if you notice its better, its prob better.

There is a slight chance this is your MAP sensor being bad, but i dont think it is.

If you do replace the map, get a delco or delphi or Hitachi brand. I bought a cheap brand and left me stranded the next day! Replace your pcv too and make sure the orings or grommet are on it, very important!

 

[BuickGirlFromMars]

If you do replace the map, get a delco or delphi or Hitachi brand. I bought a cheap brand and left me stranded the next day! Replace your pcv too and make sure the orings or grommet are on it, very important!

is 92 still like the 90? annoying to get to? or is where they put the series ii nice and ontop motor?

 

[watertree]

@MelsRegal - interesting. There is no rattle in the front and I do not believe at all that it is timing chain. I don't know how qualified the mechanics are there as it was a one time visit.

@BuickGirlFromMars - thanks for all the info here, I will look into this.

 

[watertree]

Here's an update:
TLDR - no vacuum leaks. MAF replaced with aftermarket one. No longer stalls. Engine runs terribly, always high RPM.

Full story:
I unplugged the MAF sensor and found that the car no longer stalled while driving. However, the rpm's at idle were not quite consistent. They would still spike a little (100-200 rpm +-) from time to time.

I took the car to a good mechanic this time (I know the owner and very trustworthy) and they tested everything for vacuum leaks. There were absolutely no leaks. Came back as a faulty MAF sensor (they replaced the oil sensor as well). They put in an aftermarket MAF sensor and took it for 3 road tests. It no longer stalled but the engine didn't quite feel right and he explained that to me. He suggested I drive it for a few days (if there's a problem, I will get credit for all the work done/parts used).

I drove it for 2 hours after, and it felt like the engine was shaking a lot more. I stopped in a parking lot and tried running the gas while in park, hitting 3000 RPM. With a steady foot, the RPM's became very erratic. The car then kept accelerating with the foot off the gas pedal for a few minuts. I turned it off and found the engine coolant tank boiling. After cooling off, I started the car and the RPM's stayed at around 2500 in park. Turned it off again, let it cool, rpms were around 1500, so I went into drive and then consistently at 1100. While driving, the car never decelerated unless I hit the brakes. It felt like permanent cruise control.

I am returning the car to the shop to get a factory MAF sensor which will take 2 weeks to ship. I was also informed that its possible something else may be exasperating the problems along with the sensor. It is really frustrating at this point because of the amount of time money spent on finding the problem.

 

[SAYBER]

Here's an update:
TLDR - no vacuum leaks. MAF replaced with aftermarket one. No longer stalls. Engine runs terribly, always high RPM.

Full story:
I unplugged the MAF sensor and found that the car no longer stalled while driving. However, the rpm's at idle were not quite consistent. They would still spike a little (100-200 rpm +-) from time to time.

I took the car to a good mechanic this time (I know the owner and very trustworthy) and they tested everything for vacuum leaks. There were absolutely no leaks. Came back as a faulty MAF sensor (they replaced the oil sensor as well). They put in an aftermarket MAF sensor and took it for 3 road tests. It no longer stalled but the engine didn't quite feel right and he explained that to me. He suggested I drive it for a few days (if there's a problem, I will get credit for all the work done/parts used).

I drove it for 2 hours after, and it felt like the engine was shaking a lot more. I stopped in a parking lot and tried running the gas while in park, hitting 3000 RPM. With a steady foot, the RPM's became very erratic. The car then kept accelerating with the foot off the gas pedal for a few minuts. I turned it off and found the engine coolant tank boiling. After cooling off, I started the car and the RPM's stayed at around 2500 in park. Turned it off again, let it cool, rpms were around 1500, so I went into drive and then consistently at 1100. While driving, the car never decelerated unless I hit the brakes. It felt like permanent cruise control.

I am returning the car to the shop to get a factory MAF sensor which will take 2 weeks to ship. I was also informed that its possible something else may be exasperating the problems along with the sensor. It is really frustrating at this point because of the amount of time money spent on finding the problem.

I've said this before and I'll say it again, always always always use one for electrical parts! Get yourself a delco maf and a map and change pcv, all delco parts. Get them on Amazon, MUCH cheaper and install yourself. I had this exact problem, replaced those items and has been perfect, over 4,000 miles now.

 

[SAYBER]

I've said this before and I'll say it again, always always always use one for electrical parts! Get yourself a delco maf and a map and change pcv, all delco parts. Get them on Amazon, MUCH cheaper and install yourself. I had this exact problem, replaced those items and has been perfect, over 4,000 miles now.

You coulcould also get the Hitachi brand or even delphi, which is an oem supplier, half the price of a delco maf.

 

[BuickGirlFromMars]

Everything you described came to me replacing my ECM. The prom chip I transfered to a 1988 LeSabre ECM. This was a 1990 tho. I'm just saying, you have a data communication problem. Even without the maf, it shouldn't be doing that behavior I think with warming up the pcm is having a short that gets worse with heat. Or something