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I have a 95 intrepid with 3.3l engine and 78000 original miles. The car has been very reliable until just recently. It starts normally and runs for first few minutes then begins misfiring and stalling. Engine will start back up but appears to be running on 2 cylinders. Converters get very hot during this time. Fuel pressure hovers between 36 and 40 psi. I have replaced crank sensor, cam sensor, throttle position sensor, spark plugs, coil pack, fuel pressure regulator, and all the relays, yet the problem persists. Not getting any codes. Really stumped by this problem maybe a bad ECU? Just want to see if any one else has had this problem and if so what was their solution. Really need to get this car back on the road.
 

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MAP sensor on these early 3.3 motors is a very common failure part and causes all kinds of issues like this. they all fail eventually. at the back of the intake plenum box shaped sensor threaded into the plenum. three wires. if its original then its probly bad,. easy to check with digital voltmeter or tech tool. make sure there is 5 volts and grounds to all sensors too. they all run off the ASD relay.
 

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Have replaced the map sensor along with several others and the problem still occurs. Engine runs normally for exactly 2 minutes after first start then stalls and begins to run poorly when restarted. Also the cruise light on the gauge cluster begins to flash on and off randomly during this time. This happens even if the cruise control is unplugged. Thinking the problem might be in the ECU.
 

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The flashing CC light usually indicates multiple misfires that will potentially damage the catalytic converters. Other than that info I can't really help much.

Might be the PCM. You might go on www.car-part.com and enter your vehicle information and search. Search for ECU or Engine computer in the drop down.
 

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Discussion Starter #5
That makes sense, as the engine is definitely misfiring and I suspect that raw fuel is being burned in the converter and that is why they are getting so hot. The cruise control light is driven by the ECM so I'm suspecting that is where the problem is. Also the engine runs fine for exactly 2 minutes from a cold start which is about when the cold start function times out and the ECM will go into closed loop operation.
 

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coil or wire or plug or injector. check all of them on the cylinder that the PCM says it detects the misfire on. if all parts check out good then wiring or injector driver in pcm possibly but not usually. air and coolant temp sensors and map sensor also.
 

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Discussion Starter #7
I have replaced the coolant and map sensors, I am getting misfires on cylinders 3,5,2,6. Only cyl 1,4 appear to be operating normally and they are fired by the same coil in the coil pack which is also new. The trigger signals for the coils come directly from the ECM. I suspect that one or more of the coil drivers in the ECM are going bad.
 

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Discussion Starter #8
Well now I'm at the end of my rope. replaced the ECM and it did not fix the problem. I'm out of ideas, unless anyone out there has any more suggestions. Might try taking it to a shop and see if they can do anything with it. Other than that it will likely end up in the scrap yard. Hate to see that happen it had been a good car.
 

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have you checked the o2 sensors?
only other possibility is cats starting to plug off. or maybe a blockage further along.
remove the front o2 sensors and see how long it runs. only other possibility that came to mind.
and when was the last time some injector cleaner was run through?
 

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Discussion Starter #10
Discussed the issue with an auto shop owner today and he suggested removing the o2 sensors as well, also told me to remove and clean all the ground connections. Said try unplugging the coolant temp sensor so the ecu will always think the engine is cold. Ordered a set of noid lights to check the injector function. Will post if this helps.
 

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Discussion Starter #11
Talked to an auto electrical specialist, he suggested unplugging the O2 sensors to keep the system in open loop. Also to back probe one of my other sensors to check for the 5v refrence to see if its being pulled down. Said it could even be RF interference possibly from the alternator.
 
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