92 Pontiac bucking when hot, loss of power

I've had a persistent problem with my 92 Bonneville SE (3800, 3.8L V6 engine, 4-speed tranny with overdrive, 221000 miles [no typo]) that has me perplexed. When I have been driving a while (at least half an
hour), especially in slow traffic, I lose power when accelerating. That is, I can accelerate gently and the car will operate normally. I can get it up to 95mph with no problem, if I accelerate gently enough. However, if I try to accelerate harder, the car gives me no power at all, except for a few intermittent bursts where the car will accelerate. These bursts last under a second, and are separated by several seconds with no power at all. This situation occurs at about 3000 rpm once the problem is fully developed. On its way there, the car will start to accelerate unevenly around 5000 rpm. The longer I drive, the lower the threshold becomes until it reaches about 2900 rpm. At one point, on a long road trip, it got to the point where it started doing this at about 2000 rpm, and I couldn't enter the freeway or maintain speed up a hill.
Once this happens, I can turn off the car and leave it for a while. The longer I let it sit, the better it runs, but it takes about six hours for the car to be in good condition. (Until it heats up again, of course.)
In neutral, I can rev the engine as high as I want with no problem, and the engine behaves very well when power braking. (But the RPMS are relatively low when power breaking. This phenomenon occurs at high rpm.) Before I replaced the spark plugs, the car began stalling at low speeds or when decelerating.
I've replaced the plugs, wires, MAF sensor (it was cracked anyway) and fuel filter. Starter had to be replaced at 205000 miles.
The car performed very well after I replaced the plugs and wires, but it was back after about 2000 miles. I pulled the plugs today, and there were in almost-new condition.
I don't know if this is related or not, but the transmission fluid has begun to smell burnt, especially after driving a long time. Also, in this condition, when I'm idling at a light and I release the brake, the car doesn't creep like it normally does for a second. Then I hear (and feel) a loud pop and the car begins to roll again. Oh, and the main driving belt (whatever it's called) is shorter than it should be because it bypasses the air conditioner compressor. I'm told the AC is broken anyway. I bought the car like that. (All the problems appeared after I purchased it, when it had 200000 miles on it.)
I've brought this car to several garages, but none of them have been able to reproduce the problem. As luck would have it, I drove past a garage one day while it was doing this and a mechanic was able to deal with it right away. However, leaving the car off long enough to go inside and get him was enough to let the car operate normally while he was there.
The oil pressure gauge behaves interestingly. Normally, it's at about 40psi, but when I accelerate, it VERY quickly goes to maximum, then returns to 40psi some unpredictable time afterwards.
The problem became worse after a recent oil change, but I have no idea what kind of oil was used for it. (*Grumbles about people not owning my car doing service on it*)
I have no idea what to do now. I've read that it could be my ignition system (this model uses a DIS system. There are three ignition modules that the plug wires connect to. I've examined each of them, and they all seem clean and secure. I can borrow a multimeter if necessary.
I'd greatly appreciate any advice. Thanks!
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I would check the fuel pressure also the screen in the tank could collapse after a period of driving and cause fuel flow problems. The trans, although unrelated sounds like it is going to be a problem also. Be cautious about how much repair you do to this, based on it's value.

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You're right about the value. I bought it for $700, so I shouldn't be surprised if it fails now. I think I'll junk it when the transmission finally goes. But for now, if I could just repair that problem, I'd be happy. Is there a particular tool I would use to check the fuel pressure on this model? And how would I check the screen without dropping the tank? Doing that would take all day. Thanks.
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This could be a problem with the ignition module (potentially either one or more of the coils, or the module itself). They can sometimes cause problems only after they heat up.
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To me it sounds like part of the problem could very well be DIS Module Heat Soak. I would replace the entire DIS unit with a used one.
Then I would check the coolant temp sensors, and make sure the fans are comming on and running properly. Overheating will cause power lose.
As for the transmission. You need to have the fluid flushed, and replaced. As well as the filter. Fluid that smells burnt or is discolored needs to be replaced. Charles
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QuoteMstr wrote in alt.autos.gm

When I read this post I knew I had seen the problem discussed before. I did a search of the forums that I read and I found something like this on one or two of them. I think you need to check your crank and cam sensors. The crank sensor tells the ignition system when to fire, and if loose it will misbehave. Oil pressure, I am not sure about.
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You brought up something I forgot. The crank sensors over time can lose their stringht from the magnet. At times the plastic hosing for the sensor is already broken (before removial). When that is the case, they are very difficult to remove. Yet never attempt to push on down in to the block or oil pan as a removial methiod. Charles
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Where can I find the crank position sensor, and how much does one cost to replace? Can I test one without replacing it?
Also, referring to your previous post--where can I find the DIS module itself? Are they the three small things that the plug wires connect to?
Thanks a lot, Dan
P.S. - I'm a lot closer to solving the problem now, thanks to you guys.
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lose
sensor
very
or
On a 3.8 it is on the timing cover around the crank pulley. If the plastic breaks, or is already broken they are a nightmare to remove. A few years ago I watched someone hammer one down in to an engine. Two weeks later I watched them change the engine, and that was a ASE Master Tech. As for testing it, probably not. It won't act up untill the engine is hot.

The DIS module should be behind the coil packs. Which the plug wires go to. Don't go by the tests offered by AutoZone. I took them 5 modules to test. 3 known bad, a known good, and a mystery module. All tested good on their tester.
If you plan to keep and service the car your self, buy a set of factory service manuals. It will take the guess work out of the majority of repairs. Charles
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