Eng stalls then won't start

[fxxm747]

I'm going nuts.....91 MTX stalls and won't start again until it sits anywhere from 15 minutes to an hour or so. Go to start it and it fires right up. Could be for days to a week or it could do it again a mile down the road. Anybody know what would cause this? EEC codes show PIP circuit and front O2 sensor. Other than this problem the car screams. Also, it only appears to stall when downshifting/slowing the vehicle down with the backpressure from the motor. At least it seems like thats when it always happens. Anybody....anybody???? I need help pleeeeeaase!!!

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Jim
91' Gold MTX

 

[BeatDaSHO]

yo man. when u go to start it again does it turn over and just not start? or does it not even turn over? If it turns over and doesn't start it might be your cps. This is the crank position sensor. This goes bad because your water pump leaks water and other shit onto the sensor when it heats up. This will cause it to shutoff and not be able to start until it cools down.

Greg

 

[jthomas68]

Next time it does it,look at the tach.If it drops to zero while cranking,it`s the CPS.FWIW,it will keep getting worse until it won`t start at all.

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Jeremy Thomas
Modified 91+
Pic Of The Week:

 

[sdpatt]

The PIP is the crankshaft position sensor and those are textbook symptoms you just described of it failing. While you are in there, you may want to think about the timing belt, water pump and front main oil seal if any of these are in need of or due for replacement.


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Scott

1991, 252K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
Class II hitch, Silver award at the SHOklahoma Car Show

 

[fxxm747]

Originally posted by sdpatt:
The PIP is the crankshaft position sensor and those are textbook symptoms you just described of it failing. While you are in there, you may want to think about the timing belt, water pump and front main oil seal if any of these are in need of or due for replacement.

Oh man, I know the PIP code includes the CPS, Cam position sensor & ignition module. I was hoping it was only the ignition module or the cam sensor. CPS is a big job and one I don't have time to undertake, especially where I live without the benefit of a garage. Well this helps, I didn't want to take it to the shop and have them second guess an intermittent problem and have to take it back repeatedly. Is the CPS a chronic problem? I already know I have to pull the intake manifold and replace the seals there for a different problem. Found oil in the plug holes when I changed out the plug wires. (what a bitch to route them the same way I found them). I don't spose anyones had this problem from oil on the plugs have they? I know the classic symptom of this is missing and loss of power on the low end. Anyway, thanks for the advise and if anyone has any different ideas let me know.
Thanks a MILLION!!!!!!
Jim

 

[fxxm747]

Originally posted by BeatDaSHO:
yo man. when u go to start it again does it turn over and just not start? or does it not even turn over? If it turns over and doesn't start it might be your cps. This is the crank position sensor. This goes bad because your water pump leaks water and other shit onto the sensor when it heats up. This will cause it to shutoff and not be able to start until it cools down.

Greg

Yes, it turns over fine just won't start. CPS? DAMN!!!!

 

[fxxm747]

Originally posted by jthomas68:
Next time it does it,look at the tach.If it drops to zero while cranking,it`s the CPS.FWIW,it will keep getting worse until it won`t start at all.

Actually now that I think of it I believe the tach drops to 0 like right now. Same as it does when you turn off the ignition, only you get all the lights the same as when you first turn the ignition on.

 

[fxxm747]

Originally posted by jthomas68:
Next time it does it,look at the tach.If it drops to zero while cranking,it`s the CPS.FWIW,it will keep getting worse until it won`t start at all.

OOPS, didn't read this that carefully, when you go to start it up the tach DOES show rpm. Only about 150-200 but it does show the motor is cranking. BUT when it stalls the tach goes to "0" immediately and I don't think it shows RPM when it happens when it's in gear. Like I said it usually happens with the car in gear and slowing.

 

[jthomas68]

Yup,CPS.Be ready to shell out in the neighborhood of $1000 to a mechanic,or about $400 to do it yourself in a long afternoon.

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Jeremy Thomas
Modified 91+
Pic Of The Week:

 

[AutoXSHO]

$400 to do it yourself?

Heck, I was freaked out about tearing apart the front of the motor but once I got in there it's not that bad at all.

The CPS itself is what, $50? May as well do a H20 pump too, possibly a timing belt if it's more than 60k old, but not $400 certainly.

I got the front of the motor apart in a little over 3 hours, and back together in two, and I had never done it before.

John V+

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95 MTX with mods.

 

[TedB]

If the PIP flags a code, consider replacing it.

FWIW - There is a relay pack mounted just above the radiator (black box with a wiring harness). If this unit is failing, the car will either not start intermittently, or it will stall when hot, and not start again until cool. When this unit fails, it does not flag a code, but can cause a lot of head-scratching.