96 van with 3.3L started running rough a week ago. From 20 to 40 mph the engine seems to be mis firing. Sometimes at a stop the car will stall out, but it will start right up again. At 70 mph it runs fine.

Dealer has changed plugs,wires & coil. Still runs the same.
Now they want to change the Power management module. But they won't guarantee that it will work and they want $800 to put it in.

Please help.
Bob

 

Welcome to DF
First of all, is the check engine light on? 2nd did the dealer do a compression test? And was the fuel pressure check as well. One more question, does it seem to misfire all the time? If you have any information on codes the dealer may have pulled for the controllers.

 

I would replace the Camshaft position sensor and Crankshaft sensor. They play a big roll in ignition timing, and they're only about $40 ea.

Also, sounds like an upstream O2 sensor wouldn't hurt it any either.
The O2 sensor helps the PCM determine the fuel mix by measuring the unburned fuel in the exhaust.
The O2 sensor lives in the harshest of environments, so I replace mine about once a year.
(The "upstream" O2 sensor lives closest to the engine's cylinder in the exhaust manifold.)
They cost about $50, and are a pain in the a$$ to change!
I have never changed my downstream O2 sensor.
If you see a big drop in mileage, the O2 sensor can be a major cause.

It also sounds like it could be the TPS (throttle position sensor).
The TPS acts just like a dimmer switch for a dining room light. The more peddle you give, the brighter the signal to the PCM.
They can get a dead spot and act up just as you described.
At a certain speed, rough. At other speeds, runs fine.

Also involved is the AIT (Air Intake temp sensor), EGR (Exhaust Recirculation valve), Coolant temp sensor, ect. that can cause erratic engine performance.

If you suspect the PCM is the problem, before spending $800, I suggest getting one from a salvage yard as a test.
Not to say the one from a salvage yard is good or bad, just does it run different from before.
In my experience, a PCM rarely goes bad. But it does happen.

If you suspect the engine itself is the problem, then MT's suggestion is best.
Check compression on all cylinders and fuel pressure.

One of your best investments is a Chilton's (or Haynes) repair manual for your van.
Even if you never do the work on your van, the book will help you understand how it works and what all the sensors do,
and possible effects of a failing input or output circuit.
Knowledge is power and can help you save at the repair shop.

You local auto parts store will gladly scan your PCM for error codes. (AutoZone is my fav)
Your van is OBDII, so you can retrieve codes with the "key dance" and the check engine light (the book has code definitions),
but a scan tool is best.

My '96 GCV has 200,000+ miles and still runs great!
Hope this helps you get your's running great again too.
Let us know what they find,
PinCup

 

plugged converter and/or plugged egr, very often no codes come up for them even though they need servicing. throw a can of seafoam from autozone in the gastank and drive it before anything else I think. also, check your coolant level and coolant temperature sensor, as engine temp is used to calculate air fuel ratio. timing belt slip very possible also. very good that we can eliminate spark as the issue since plugs wires and coil were changed. I'm leaning to three things, dirty fuel injectors, plugged egr and plugged catalytic converter. if you haven't ever changed o2 sensors, do it anyway, they are cheap and make a great difference in milage. order them someplace cheap online and while you're waiting for them, use the seafoam. you'd be amazed what it can do. it is not as good as BG44k, but right up there in ability to clean injectors. if you're the do it yourself type, try removing the first catalytic converter and see if you can see a light through the holes. if you can't, it is plugged and needs to be changed or drill a 1/2 inch hole from input to output with a long bit on a drill. but first things first, try the seafoam. spark will be of little benefit if you're not getting enough fuel due to plugged injectors

 

Just added Seafoam to the Gas tank. Will report back later if their are
any changes.

Thanks,
Bob

 

Thanks for all the suggestions.

Seafoam didn't make any changes. The van is still running the same.
Starts fine,but starts running rough at about 25mph and you can feel it through 45mph. At 70mph it runs fine. As soon as I slow down around 15mph the tach starts dropping below 300 and then shoots back up to 1200. Then the engine dies. Starts right up again!
Trying to decide what to do next. Should I just change out the PCM or should I start with the sensors? Oxygen sensor, Crank shaft sensor?
No codes are showing.

Help!
Bob

 

Bob
Is the check engine light on? If it is what are the codes?

 

Check engine light is not on. No codes.
When I picked up the car from the dealer he said no codes were showing.

Thanks,
Bob

 

It is speed related? it is possible it is a transmission problems.
gotta love mechanic that just ask ppl to "try this" and "try that" without even running proper diagnostic.
don't plunge down $800 without knowing it is the problems. and I don't think PCM would be the problem. If you HAVE to try it, I think on 96, you can pull a junkyard PCM a van with same motor, and it will work, ask ur dealer.

also, does engine REV freely without hesitation in Park?

mastertech, do you remember if 96 caravan has common "crack flexplates" problems? or was that only on like 1998 ish models.

 

It could be almost anything that be causing your problem, It does help if there were some codes. It could be fuel, throttle body dirty, AIS motor, crank or cam sensors. Or could be a cracked flex plate. These are only guess's. I wouldn't spend anymore until you find out the cause.