Chrysler Repair: Repeated CPS Failure on 3.0L V-6:no start, crank sensor, plymouth voyager

Question
QUESTION: Hi,

I have a 97 Plymouth Voyager and I am having repeated crank sensor failures (3.0 engine with 3 speed transmission).

I replaced the crank sensor once, and about 20-30 minutes later the engine shuts off. I was getting no spark so I replaced the CPS again. It ran for 20 minutes and shut off again.

I then replaced the computer & cps & asd relay and it shut off 5 minutes later. I replaced the CPS once more and checked all the wiring and again it shut off 5 minutes later!

It shuts off while idling (luckily) I've been hesitant to take it down the road.

I searched google everywhere and it seems like no one has had a similiar problem before. Can you think of anything else to try? What would cause a CPS to fail so quickly? I install new sensors with shims on the tip. I tried letting the car cool off a whole day but it doesn't work. Once the CPS fails it's done with, it has to be replaced.


Thanks!
Dennis

ANSWER: Hi Dennis,
What is happening to the shims on the tip? Are they wearing away, or are they untouched? If wearing away quickly and totally then I would suspect that there is too much play in the rear crankshaft bearing or some such out-of-roundness that is damaging the tip of the cps. If not showing any signs of wear then you are probably not pushing the tip of the cps firmly against the flex plate surface to make contact and so the signal is too weak. Other than that you could check the voltage that is being applied to the orange wire to be 8V or so.
Those are the only possibilities that I can see that would damage it.
Roland
PS Please let me know what you find.

---------- FOLLOW-UP ----------

QUESTION: Hi,

I was getting 4.9 volts on the gray/black wire, nothing on the orange wire.

I took the latest CPS out and the shim was still on it. I tried putting it back in and pressing down on it while torquing it but nothing would work. I think the CPS is already bad just like the previous ones.

The CPS before this one had the shim removed but no scratches or anything. This problem developed all of a sudden after I washed the engine compartment out. I didn't have any problems such as oil leaks or rattles.

I did check the wire harness and it looks fine. Could anything else besides the computer cause the CPS to die so quickly?

Any advice is more than welcome at this point.

Thanks,
Dennis

ANSWER: Hi Dennis,
There has to be some sort of voltage on the orange wire at the plug (with plug removed but ignition switch on) otherwise you wouldn't have 4.9 on the gray/black. So check that out again for having 8V. Then try measuring the voltage on the gray/black while you turn the crank pulley bolt over by hand to test whether the cps is sensing the motion of the flex plate. It should oscillate the voltage on that wire from 4.9 to 0.3 and back repeatedly per revolution. If it is doing that then the cps is OK. Then check that there is a good connection from the gray/black to pin 32 of the pcm, and verify by piercing the insulation at that pin on the pcm plug that you are getting that pulsing at the pcm itself. If so, then the cps is good and so is the signal to the pcm. You might want to remove the pcm plugs and spray them and the sockets with electronic circuit board cleaner and let it evaporate away. There may be some shorts in those connections resulting from the wash job.
Roland

---------- FOLLOW-UP ----------

QUESTION: Hi,

I checked all the wiring and it was fine. I replaced the computer, ignition coil, ASD relay, distributor, Crank sensor. I replaced all that because now it doesn't want to turn on even with a new Crank sensor... what else can I change? I thought that was about everything in the ignition system. Something is wrong somewhere.

I don't have much test equipment except a multimeter and code scanner.

Thanks,
Dennis

Answer
Hi Dennis,
Just on a chance try turning the ignition key:"on-off-on-off-on and leave on, doing that in 5 seconds or less elapsed time. The watch the check engine light, which remains 'on', to see if it begins to flash, pause, flash, etc. If so, count the number of flashes before each pause. Then keep repeating until you are sure of an accurate set of flash counts. Then tell the counts in the order of appearance.

How about the voltages that I suggested measuring. Are they OK?
Do you hear the fuel pump run when you turn the key to 'run', for about 1 second?
Do you have spark when you are cranking it over.
Have you checked the egr valve to see if it moves. Look for the egr in the small pipe that branches off the exhaust manifold on
the side nearest the radiator, and goes across the front of the engine. It's body is in the pipe, then there is a flange connecting the body to the round vacuum actuator of the valve. Look inside the flange and you will see a rod with a slot which is the valve stem. Spray some WD-40 on the stem where it enters the valve body and then take the tip of a screwdriver and put it in the slot of the
stem and move the stem back and forth to free-up the action. You will feel spring-action which is trying to close the valve to a dead stop. Make sure it moves to a dead stop position (closed), then try and start it up.
Those are some ideas which I hope you will pursue before buying any more parts.

Roland