1996 Cadillac Deville No Spark unless one crankshaft sensor

Tiny
MBANKH
  • MEMBER
  • 1996 CADILLAC DEVILLE
Computer problem
1996 Cadillac Deville V8 Front Wheel Drive Automatic

Hello. I have ran into a very strange problem that I have never seen before. I have a 96 deville I am working on that is a no spark situation with no codes present and no cranking rpm on scantool. If I unplug either crankshaft sensor the car will have a long crank but will start and run. Both crank sensors are 1140 ohms. Wiring to them from module is good and not shorted. Cam sensor is also in spects. I have looked in the crank sensor holes with a mirror and reluctor looks to be ok. The module has been changed with a known good one. All six wires from pcm to module also are good No shorts to ground or voltage. Pcm is also substitured with a known good one I have the most recent update flashed to it. I did ac voltage checks at the module plug with car idling on each open sensor. Crankshaft sensor a reads 5.1 volts when car is running and sensor b around 7 using a fluke 87 meter. I had two more cranks sensors on hand and tried them. Same results. Seems like a crank sensor sync problem of some kind. I have disconnect cam sensor with both cranksensors plugged in and no cranking rpm or spark. Has anyone ran into this? Seems very odd. Almost like the reluctor is a problem but I don't see how when it will start with either crank sensor just not both. Hope someone can give me a direction.
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Friday, August 7th, 2009 AT 9:04 PM

2 Replies

Tiny
FACTORYJACK
  • EXPERT
Thats a good one, haven't seen anything like it to this date. If you can, pull the cam sensor and see if the pin came out of the sprocket. It seems that it would still start, it just may be extended crank due to loss of #1 sync pulse. I had that happen in the past, can't remember the vehicle it was on. What is the history on the vehicle, did this all of a sudden occur, or has someone been in it before you. Is it capable of setting codes, does it set codes when you disconnect sensors. Are the crank sensor connectors reversed perhaps? I can't figure what disconnecting one crank sensor would change, since they are signal generators, unless it is defaulting. Is the ground strap to the module base present? These are just some ideas.
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Friday, August 7th, 2009 AT 10:51 PM
Tiny
MBANKH
  • MEMBER
Thanks for the reply. Yes it does generate a code for missing crank sensor 1 or 2 can't remember the code at the moment and displays service ignition system in message center. If I clear the codes they do not reappear until I create them. The history is that everyone has had their hands in it. Thats why I hung another pcm on it and flashed it. Ground strap is present. Power and ground to the plug good. No voltage drops. I had a 94 northstar in yesterday that was running so I wanted to see if I disconnected the 6 wire connector to the module if it would still have spark in base mode and that car did. This one don't. Can the reluctor become magnized and create havok? I don't know. Im usually pretty good at this stuff but this one seems to lead back to the reluctor. I would love to solve this. I don't like losing. Not to mention what if another comes in with the same problem. Thanks again for the reply. They were all very good ideas.
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Saturday, August 8th, 2009 AT 6:52 AM

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