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Unread 10-19-2013, 06:41 AM   #16
Jer-Bear
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PCM is dead, get a rebuilt one and have it programmed to your VIN. No cheap way of getting out of this one I'm afraid, I had the same problem. Use a meter to check your TPS for any juice, if it has nothing, your PCM is definitely dead.

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Unread 10-19-2013, 06:54 AM   #17
doityourselfMM
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How long has it been sitting? You say it ran fine, and then sat for a while?

If the battery has enough charge to turn over the engine, then I don't suspect it's a voltage supply problem. And I'm not sure, correct me if I'm wrong, but the starter shares a common grounding bond with the engine block. So it the starter turns, the grounds are OK to the block.

I'm still concerned about no gauge activity. Jer-Bear and 86cj74.2L might be on the right track with the PCM. Or the voltage supply to the PCM. Fuses? Oxidized connector pins?

Keep the 'updates' coming. Between us all, we'll get to the bottom of it.


EDIT - Just checked the FSM for my 99 4.0. The Automatic Shutdown Relay supples voltage to the ignition coils. (The OP said he had no voltage there.) The ground circuit to operate the ASD relay is controlled by the PCM. The PCM regulates ASD relay operations by switching its ground circuit on-and-off.

Prior to looking at the PCM, you can check Fuse 6 (30A) in the Power Distribution Center. It supplies voltage to the ASD relay. You can also check the relay which is also in the PDC. The switched relay contacts then feed voltage to Fuse 26 (15A) also in the PDC. This fuse supplies voltage (finally) to the PCM. All easy stuff to check with your volt meter.
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Unread 10-27-2013, 09:43 PM   #18
pitsy
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Minor update: Confirmed the issue is electrical by spraying starter fluid into the TB while cranking. Battery voltage was 11.6V, so I pulled it and had it load tested. Bad battery. New battery installed turns it over better, but still no start.

BUT, there is full system voltage at the coil rail connector. Using my spanking-new FSM, I was able to check every fuse and relay in the starting/ignition circuits. I also jumpered system voltage into the ASD relay output slot in the PDC and measured no voltage drop between there and the coil rail connector.

I've disconnected and cleaned all the harness connectors on that side, and everything hooked up to the TB, plus every connector going into the junction box on the firewall. Still no start.

I'm finally having it towed to my place so I'll be able to work on it more comfortably. I'm about to get medieval on that wiring harness.

Oh, to answer the question about the instrument cluster: When I turn the key to ON, the odometer displays mileage and various warning lights illuminate briefly. No readings on the fuel gauge, battery gauge, or the other needle-type gauges.
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Unread 10-27-2013, 10:47 PM   #19
Jeeples
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Quote:
Originally Posted by Jer-Bear View Post
PCM is dead, get a rebuilt one and have it programmed to your VIN. No cheap way of getting out of this one I'm afraid, I had the same problem. Use a meter to check your TPS for any juice, if it has nothing, your PCM is definitely dead.
Not entirely.

You can get a used ECM from a junkyard and have it flashed to your VIN. I recently did this with a WJ I bought for cheap due to a no start condition. I paid $35 for the ECM and $65 for the flash at a local parts store.

Worst case scenario take it to a local dealer for the flash. All my local ones quoted me $100 to do it.
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Unread 10-27-2013, 10:54 PM   #20
Jeeples
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Quote:
Originally Posted by pitsy View Post

Oh, to answer the question about the instrument cluster: When I turn the key to ON, the odometer displays mileage and various warning lights illuminate briefly. No readings on the fuel gauge, battery gauge, or the other needle-type gauges.
Sorry posting via mobile so no multi-quote.

The no readings from the fuel and battery gauges typically means the ECM is not powering up. Like Jer-bear mentioned you can check for 5V power at the TPS with the key on to determine if the ECM is functioning.

If the ECM is dead, refer to my earlier post.
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Unread 10-27-2013, 11:49 PM   #21
Jer-Bear
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Quote:
Originally Posted by Jeeples View Post

Not entirely.

You can get a used ECM from a junkyard and have it flashed to your VIN. I recently did this with a WJ I bought for cheap due to a no start condition. I paid $35 for the ECM and $65 for the flash at a local parts store.

Worst case scenario take it to a local dealer for the flash. All my local ones quoted me $100 to do it.
I'm talking about the PCM, Power Control Module. It controls the engine and electronics. If its out, you can't just pull one. It has to be rebuilt.
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Unread 10-28-2013, 09:06 AM   #22
Jeeples
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Quote:
Originally Posted by Jer-Bear View Post
I'm talking about the PCM, Power Control Module. It controls the engine and electronics. If its out, you can't just pull one. It has to be rebuilt.
Yeah, the guy mounted against the firewall on the passenger side. Technically it's called the Engine Control Module, since WJ's have a seperate Body Control Module and Transmission Control Module. On older vehicles the correct nomenclature is PCM (Powertrain Control Module) since both the engine and transmissions (where applicable) were controlled by one computer.

Semantics, I know, but it can cause confusion.

But you are incorrect, if your ECM goes out, your only option is not a rebuilt unit. You can pull a used ECM out of the same MY WJ (and same drivetrain) and have it reflashed to your VIN. I ended up paying roughly 1/3 the price by doing this vs. going with a reman.

And yes, you are taking a risk buy purchasing a used ECM, and I would only suggest doing this if you have a decent supply of WJ's to pull from. Of course if your local yard charges a lot for used ECM's it might not even be worth it.

EDIT:

A quick and dirty test to see if your used ECM is good would be to plug it in to your WJ and turn the ignition key on. If the fuel and battery gauges come on, you should be good to go. You could also start it, but it will only run for a few seconds before the SKIM shuts it down.
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Unread 10-28-2013, 09:32 AM   #23
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Forgot to mention, you may want to check the wiring harness for the cam position sensor, crank position sensor and the O2 sensors. Sometimes the harnesses get damaged and shorts the power to ground, which can cause symptoms similar to a dead ECM.
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Unread 10-28-2013, 10:19 AM   #24
Jer-Bear
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Quote:
Originally Posted by Jeeples View Post

Yeah, the guy mounted against the firewall on the passenger side. Technically it's called the Engine Control Module, since WJ's have a seperate Body Control Module and Transmission Control Module. On older vehicles the correct nomenclature is PCM (Powertrain Control Module) since both the engine and transmissions (where applicable) were controlled by one computer.

Semantics, I know, but it can cause confusion.

But you are incorrect, if your ECM goes out, your only option is not a rebuilt unit. You can pull a used ECM out of the same MY WJ (and same drivetrain) and have it reflashed to your VIN. I ended up paying roughly 1/3 the price by doing this vs. going with a reman.

And yes, you are taking a risk buy purchasing a used ECM, and I would only suggest doing this if you have a decent supply of WJ's to pull from. Of course if your local yard charges a lot for used ECM's it might not even be worth it.

EDIT:

A quick and dirty test to see if your used ECM is good would be to plug it in to your WJ and turn the ignition key on. If the fuel and battery gauges come on, you should be good to go. You could also start it, but it will only run for a few seconds before the SKIM shuts it down.
My mechanic lies then, thanks for the info!!
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Unread 10-28-2013, 10:20 AM   #25
Jer-Bear
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Quote:
Originally Posted by Jeeples View Post
Forgot to mention, you may want to check the wiring harness for the cam position sensor, crank position sensor and the O2 sensors. Sometimes the harnesses get damaged and shorts the power to ground, which can cause symptoms similar to a dead ECM.
^^^x5 My cam sensor wiring was rotted away from being soaked with oil and shorted it all out. That's what killed mine.
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Unread 10-28-2013, 12:02 PM   #26
pitsy
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Thanks for the help everyone. I do have a good source for a used ECM, if it comes to that. But like I mentioned, there's a lot of corrosion going on so I'm gonna subject the wiring harness to some serious scrutiny. I'm really excited about having it towed to my place tomorrow! It'll be right outside my back door, with an autozone on the next block.
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Unread 10-28-2013, 12:33 PM   #27
Solomon
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Not sure if your issue is resolved yet but I had a similar issue with my WJ about a week ago. I had to have it towed to a shop. They determined that it was the crankshaft position sensor. They changed it out and now I'm good to go. hope this helps
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Unread 10-28-2013, 03:31 PM   #28
Jeeples
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Quote:
Originally Posted by pitsy View Post
Thanks for the help everyone. I do have a good source for a used ECM, if it comes to that. But like I mentioned, there's a lot of corrosion going on so I'm gonna subject the wiring harness to some serious scrutiny. I'm really excited about having it towed to my place tomorrow! It'll be right outside my back door, with an autozone on the next block.
Good luck!

Also, just double check all the grounds, make sure they good and clean. There's also a ground attached to the ECM case as well.
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Unread 10-30-2013, 12:20 AM   #29
pitsy
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OK, it's been delivered to my place, safe and sound. I've got a flat, clean workspace (outdoors), electrical outlets for tools and lights, and a fridge and internet twenty feet away. If I have time tomorrow, I'll take a good set of "before" pictures inside and out to document this project. I'll continue this thread until I get the thing running, but I'll start a new thread for the overall project.

The theme for this project is "Shoestring, Junk-Yard, Handmade". The sub-theme is "When was your last tetanus shot?".
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Unread 11-07-2013, 02:31 PM   #30
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