1989 LeSabre T-Type maintaining RPM problem

[hoss77]

My 1989 LeSabre T-Type 3.8 engine does not maintain it's RPM. As soon as you start the car the RPM goes to zero and dies. If I press on the gas pedal and keep the RPM up above 1,000 the car runs rough and misses but keeps running. When I let of the gas pedal, the RPM drops, the car sputters, back fires, the RPM drops to under 1,000 then to zero the engine dies and the catalytic converter gets real hot and turns orange.

Prior to the above happening my check engine light came and I had a diagnostic check done that indicated the cam sensor was faulty. I kept running the car with the faulty cam sensor. Eventually the car started to miss at all speed that got worse and the engine finally died. I drove the car home by keeping the RPM above 1,000. I then changed the cam sensor, changed the fuel filter and idle air control valve, but still same problem.

Sure could use some help!

Thanks, Hoss77

[rustbucket]

If it was a distributor car, I would think the timing was off, but now the computer controls that. How many miles? How does it start? Did this come on all at once, or gradually over time. It sounds like the spark is not working correctly and dumping raw gas into the catalytic converter.

[hoss77]

Originally Posted by rustbucket

If it was a distributor car, I would think the timing was off, but now the computer controls that. How many miles? How does it start? Did this come on all at once, or gradually over time. It sounds like the spark is not working correctly and dumping raw gas into the catalytic converter.

The car has 71,000 miles, to start the car I have to step on the gas pedal and keep the RPM above 1,000 to keep it runnung and the engine surges from a high to low RPM even with the gas pedal accelerated, but if I keep the RPM above 2,500 RPM the engine runs pretty smooth. The car started to miss very slightly about three weeks ago and gradually got worse when driving and then the car died on a shopping trip as I put the car into reverse and thats when I had to keep the RPM up to keep the engine running. What would cause the car not to spark correctly to dump raw gas into the exhaust? Also, the exhaust does have a strong smell of unburnt gas fumes!

[rustbucket]

Have you changed the sparkplugs and/or sparkplug wires?

[hoss77]

Originally Posted by rustbucket

Have you changed the sparkplugs and/or sparkplug wires?

I changed both the sparkplugs and the wires about 6 months and the o2 sensor about 3 months ago.

[rustbucket]

When starting, if you didnt touch the pedal, does it start and then die, or does it not start at all. Does it almost start?

[hoss77]

Originally Posted by rustbucket

When starting, if you didnt touch the pedal, does it start and then die, or does it not start at all. Does it almost start?

On the first attempt, the engine attempts to start and then on followup attempts the engine just cranks.

[michtom]

check your exhaust back pressure, possible bad convertor

[hoss77]

Originally Posted by michtom

check your exhaust back pressure, possible bad convertor

Started the car and there's a lot of back pressure from the exhaust.

Thanks for the response!@

[rustbucket]

How does one check back pressure from the exhaust?, and what is too much?

[Hypsi87]

Check your MAF

[Magnus42]

Man, I joined this whole thing just to tell you this.
My '89 T-Type did the same thing and it ended up costing me a rod throught the oil pan. I hope it isn't too late.

The computer cotrols the timing, yes. But with mine, I had a leak in my radiator, and it overheated really bad one day after some... hard driving. It broke down the oil and generally messed the engine up. It warped my timing chain cover, and I replaced the cam sensor 3 times. What happened, is I think the cover being warped rubbed something, cause there was a jagged edge at the end of the cam shaft. It threw the magnet off the camshaft when it warped, and that coupled with the cover being warped caused the timing to be off. It wouldn't run right and randomly died. I had no choice at the time but to drive it with the timing off... horribly off. It eventually threw a rod cause of the timing. So check your cam shaft. The sensor you replaced is a magnetic sensor, and if the magnet it corresponds to has fell off, the you're gonna have big problems until you get a new camshaft.

[avatar307]

You may want to pull the timing cover off and confirm that it is aligned properly and none of the teeth have sheared off. I know of several late-70s to early-90s vehicles which some strange timing gears. They were like alunimum alloy with a hard nylon shell on the teeth to keep them from wearing.

Eventually the teeth just start sheering off and it throw your valve timing out of whack. That could result in raw unburned gas fumes being dumped into your exaust, as well as misfires and all sorts of other things.

If such is the case, you're catalytic converter needs replaced. Anytime anything other than exaust fumes are introduced into the exaust system (gas, coolant, metal shards, oil, etc) your catalytic converter will be clogged and need replaced to make your engine run properly. (See exaust back pressure above.)

Beyond that, you may want to check the vacuum lines to your EGR valve as well as replacing the EGR. If it's behaving extremely poorly, can cause some syptoms like this, but not near as severe.