Starting Troubles, CPS?

Eliminator89 · Feb 3, 2004

Drove into town a few days ago. Truck ('89 MJ, 4.0, 5spd, 2wheeldrive, 125k miles) ran fine, no indication of any trouble. When I came out of the store, the truck would not start. It cranked just fine. I tested for spark, nothing. I looked around the engine compartment, nothing obvious. I checked a bunch of connectors, unplugging, plugging them back in in case of a faulty connection. Nothing helped.

Approximatly 3 hours later, my brother showed up with the trailer. We tried it again, no spark, no start. We hauled it about 20 miles to a friend's farm where he has a heated (Minnesota) shop. Pushed it off the trailer, tried it again, it started right up.

Oral Roberts was nowhere in sight so the Comanche healed itself. From what I have read by searching the archives here, it would seem the crankshaft position sensor is the most likely culprit.

What do you guys think?

I am going to clean all the connectors I can find. I may also change out the existing sensor for reliability's sake and keep a spare along with the neccessary tools. This sensor seems to be a fairly common problem.

JimC · Feb 3, 2004

Eliminator89 said:
Drove into town a few days ago. Truck ('89 MJ, 4.0, 5spd, 2wheeldrive, 125k miles) ran fine, no indication of any trouble. When I came out of the store, the truck would not start. It cranked just fine. I tested for spark, nothing. I looked around the engine compartment, nothing obvious. I checked a bunch of connectors, unplugging, plugging them back in in case of a faulty connection. Nothing helped.

Approximatly 3 hours later, my brother showed up with the trailer. We tried it again, no spark, no start. We hauled it about 20 miles to a friend's farm where he has a heated (Minnesota) shop. Pushed it off the trailer, tried it again, it started right up.

Oral Roberts was nowhere in sight so the Comanche healed itself. From what I have read by searching the archives here, it would seem the crankshaft position sensor is the most likely culprit.

What do you guys think?

I am going to clean all the connectors I can find. I may also change out the existing sensor for reliability's sake and keep a spare along with the neccessary tools. This sensor seems to be a fairly common problem.

If unplugging and replugging the CPS connector didn't help at the time (not sure if that was one of the connectors you tried), I don't think you can safely say it's a bad CPS. When mine started going bad, the unplug-replug routine worked for a few months before it died completely.

Eagle · Feb 3, 2004

The CPS is the most likely culprit, but it could also be the ignition module. On an '89 you should be able to test the CPS with a multimeter. Look for a resistance of around 200 to 250 ohms cold. When craking, it should generate a low (less than 1.0) voltage -- a search might indicate what the spec is, because this was discussed recently.

Although CPS failures are ofetn encountered, I would not classify it as a "problem." They typically go 100,000 miles or more before requiring replacement. Other than a length of wire, I don't think it's fair to expect any electrical component to last forever.

For that reason, when I replaced mine I bought two, and I carry the spare with me.

Eliminator89 · Feb 4, 2004

I don't beleive the CPS plug was one I tried. I haven't been able to get to it today due to a home plumbing repair I had to do today. The ones I unplugged were on the throttle body and the coil.

If I get this plumbing job done tomorrow, I'll be able to dig into the truck again with a good multi-meter.

Eagle · Feb 4, 2004

The CPS is mounted in the top of the bellhousing. If you visualize sitting in the driver's seat and using x-ray vision to look through the firewall at the engine, the CPS sits at abput the 11:00 o'clock position.

Two wires lead up from it, at the back of the head/intake manifold. There's a GM-style environmental connector, from which the wires continue into the main wiring harness. The connector itself is a 3-terminal connector, but one terminal isn't used.

8700XJS · Feb 14, 2004

Eagle said:
The CPS is the most likely culprit, but it could also be the ignition module. On an '89 you should be able to test the CPS with a multimeter. Look for a resistance of around 200 to 250 ohms cold. When craking, it should generate a low (less than 1.0) voltage -- a search might indicate what the spec is, because this was discussed recently.

Although CPS failures are ofetn encountered, I would not classify it as a "problem." They typically go 100,000 miles or more before requiring replacement. Other than a length of wire, I don't think it's fair to expect any electrical component to last forever.

For that reason, when I replaced mine I bought two, and I carry the spare with me.

Would there be any spark present if the CPS was bad. I am getting spark and fuel when cranking but no start.

Ed in North Ga. · Feb 14, 2004

8700XJS said:
Would there be any spark present if the CPS was bad. I am getting spark and fuel when cranking but no start.

no, spark=good CPS

you got spark, and fuel, and its not starting?

youve got ghosts.

are you getting anything at all? backfire? one would think if theres gas in the hole, and a plug firing, all would be good.

8700XJS · Feb 14, 2004

What happened was she was running and I pulled the connector off the idle stepper motor. I hooked it backup and it died. I have not been able to get it to start since. I have ordered an Engine Control Unit. It should be here tomorrow.
We'll see.

I did check the spark at the distributor and the plugs. I also checked for gas in the fuel rail. No problems with either. My thought is I blew up the ECU somehow by disconnecting and reconnecting with the thing running.

Kenny

Ed in North Ga. · Feb 14, 2004

8700XJS said:
What happened was she was running and I pulled the connector off the idle stepper motor. I hooked it backup and it died. I have not been able to get it to start since. I have ordered an Engine Control Unit. It should be here tomorrow.
We'll see.

I did check the spark at the distributor and the plugs. I also checked for gas in the fuel rail. No problems with either. My thought is I blew up the ECU somehow by disconnecting and reconnecting with the thing running.

Kenny

Ive done that-didnt hurt mine- the stepper motor is just idle anyway- a maybe...maybe not....
curious- you got spark, you got gas at the rail, but the gas isnt in the holes, is it? that would be either the CPS, or the thingy in the distributor that picks up the rotation(like hall effect-ford/only its jeep)- this makes the injectors wake up and squirt.

bottom line- the injectors arent fireing- check the CPS for proper ohms. If its down and out, the ECU dosent know the engine is turning over, and wont fire the injectors- And dont hold the throttle to the floor. That shuts them off as well.

badge714 · Feb 14, 2004

Starting Troubles Cps

HI I THINK WHAT ED FROM GEORGIA IS REFFERING TO IS THE CAMSHAFT POSITION SENSOR. IF THE CAMSHAFT SENSOR IT WILL NOT STARt. UNLIKE THE CRANKSHAFT POSITION SENSOR wHICH WILL ALLOW IT TO START. THE CAMSHAFT POSITION SENSOR. IF THE CAM SIGNAL is LosT WHILE THE ENGINE IS RUNNING <THE PCM WILL CALCULATE SPARK TIMING BASED ON THE LAST CMP SIGNAL & THE ENGINE WILL CONTINUE TO RUN> HOWEVER THE ENGINE WILL NOT RUN AFTER IT IS SHUTOFF. DALE -----
[email protected]

8700XJS · Feb 15, 2004

Ed in North Ga. said:
Ive done that-didnt hurt mine- the stepper motor is just idle anyway- a maybe...maybe not....
curious- you got spark, you got gas at the rail, but the gas isnt in the holes, is it? that would be either the CPS, or the thingy in the distributor that picks up the rotation(like hall effect-ford/only its jeep)- this makes the injectors wake up and squirt.

bottom line- the injectors arent fireing- check the CPS for proper ohms. If its down and out, the ECU dosent know the engine is turning over, and wont fire the injectors- And dont hold the throttle to the floor. That shuts them off as well.

Well I got it working. It was the ECU. Somehow when I unplugged and plugged the connector back in I killed the ECU. I got a new (rebuilt) one from NAPA at a cost of $125. The stealership wanted $308 for the same thing. In my wonderful trouble shooting I determined that the fuel pump was bad. Should of changed the ECU first. Oh well I have a new fuel pump now.

Kenny

Starting Troubles, CPS?

Eliminator89

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JimC

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Eagle

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Eliminator89

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Eagle

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8700XJS

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Ed in North Ga.

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8700XJS

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Ed in North Ga.

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badge714

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8700XJS

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