94 V8 Jeep - No Spark - New CPS sensor

Old 05-09-07, 03:20 PM
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Question 94 V8 Jeep - No Spark - New CPS sensor

My son has a 94 Jeep Grand Cherokee V8 that I thought had a bad Crankshaft Position Sensor (CPS). I found the old sensor is located on top of the bell housing for a V8. I installed a new CPS sensor and the car started immediately. I ran it for 30 minutes and I turned it off. Restarted fine once. Now new problem. When I put it in reverse, the car backed up and when I put it in drive the car instantly died - again no spark. Check engine code only shows battery disconnected recently. My son had almost the same thing happen before it quit last time. He put it in reverse and the car stalled and it wouldn't start. Now new CPS and same problem again. Is it possible that putting the car in reverse can have anything to do with the problem?

The new CPS was for a Dodge 318 that cross references to work on a 94 Grand Cherokee V8. The plug connection was different, but the sensor body looked identical; so I switched the plug and soldered the wires. As stated above the car started fine with the new sensor, so I don't think switching the plug on the sensor is the problem.

The car engine had a complete rebuild about a year ago and ran great. The car first stopped after a fender bender and my son had it towed to his home. When I worked on trying to get it started, I found it had spark and power to the coil for only one second. After one second, the autoshutdown relay clicked off and there was no spark or power to the coil. I put a jumper wire to power the coil positive wire to get the car started to get it to my home. I took off the jumper wire at home and it started right up and ran OK for 2 weeks before the same problem started again when putting the car in reverse it stalled. This time I towed it to a garage but they didn't want to work on it after I told them I had put power to the coil to get it home, but they thought it was likely the Crankshaft Position Sensor (CPS). I read a number of similar posts and it sounded likely so I got a new sensor and installed it.

In response to my first post, one suggestion was to replace the camshaft sensor. Not sure what to try next. Is there a coil energizing relay?
Old 05-09-07, 04:51 PM
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Did you see my post to your other thread?

Seems you are having bad luck with the vehicle....

When the vehicle stalls when put into a gear, it is usually the lock-up solenoid or the torque converter.

Though....with the other issue you were having, it may be computer (module) related.
Old 05-09-07, 06:13 PM
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Mark thanks for the post

Thanks for the reply. I would guess that if the lock-up selenoid was the problem, I could restart it after it stalled? The problem is it has no spark or power to the coil again - as you say I was considering the ECM but it started fine and restarted once after the new Crank Postion Sensor (CPS) was installed.

Would the ECM work intermittently and then stop working? I can try a new ECM, but I would guess that either the crank sensor replacement did not install properly (allowing ~1 restart) or the ECM is shutting down the coil for some other reason. The articles I find say the crank sensor tells the ECM when to fire the coil and sends the signal to the ECM to complete the ground to power the coil.
Old 05-10-07, 02:46 AM
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its possible you could have a wiring problem as they tend to show up from the little movement of the engine when placed in reverse or drive would check the wiring closely for bare spots around the engine bellhousing area where it may have rubbed through.
would probably check codes if the computer isnt receiving a crank signal it should set a code 11 believe you can still check codes on your 94 model by just cycling the key on and off three times leaving it on at the end of the cycle.
might also check for spark at the coil instead of at the plug or coil wire as the coil does go bad fairly often on dodge and jeeps, and will usually show a weak spark at the coil but not nearly enough to make it to the spark plug.

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