ScienceMagic

This will be a long and involved post, but I hope someone knowledgeable about these things can help me out!

I've owned my 1999 Dodge 3500 Van since new. It's had some major rust problems in the front end, due to being driven in Midwest winters. I had the front end replaced this summer, which involved removing the engine and transmission, sawing off the front frame just behind the spring perches, and welding on a clean frame piece from a van that lived in Georgia. Total cost was over $13,000. I figured it was worth it, since a new camper van would run over $100,000.
When the shop put everything back together, including the PCM (which they had removed), the engine would only run if the "signal" or "sensor" ground wire was physically grounded to the vehicle ground with a jumper wire. That wire would get quite hot, indicating a LOT of current going through it, which doesn't seem right. The sensor circuit shouldn't have a lot of current.

I checked the PCM ground wires by unplugging the connector and checking the pins with a multi-meter. They indicated continuity to ground. So it seems like the PCM is well grounded, but I don't know how to tell if the PCM ground is still good INSIDE the PCM.

I found the ground wire on the camshaft sensor, and was able to get the engine to run fine if I grounded this wire to the engine. This wire is called "sensor return" on the wiring diagram. If I disconnect the jumper, the engine will crank, but not fire, and the auto shutdown relay will constantly chatter (I tried replacing it already), and a "no bus" indication on the odometer. Connect that jumper wire, and I can hear the fuel pump switch on, and the engine starts right up.

I decided that the PCM must be bad, so the frame shop bought an un-programmed PCM from Auto Zone, and took the van to the dealer to have it flashed. The dealer has had it for over a week, and they claim the replacement PCM won't accept their programming. They have pretty much given up, and the van is sitting in their parking lot (400 miles away from me!). They cannot get the engine to run with the new PCM (so they say). Auto Zone has since told me that sometimes their aftermarket PCM's just won't accept dealer programming.
By the way, I replaced the PCM two years ago due to a "no bus" message on the odometer. I tried an Auto Zone unit, which didn't work right, and ended up paying for one from Mopar.

My theory is that the old PCM is somehow not getting grounded, unless I ground the sensor circuit, and then all the power the PCM needs is coming through the sensor circuit, instead of the normal PCM grounds. I don't think it should be driven that way, as I would think the sensor circuit traces on the PCM circuit board might get burned up.

If my theory is correct, then nothing that the PCM controls should work, am I correct? Like the fuel pump wouldn't work, which I have confirmed, or the fuel gauge, which I don't recall.

Auto Zone sent me a pre-programmed PCM that I have next to me, and I plan on driving to the dealership this week and trying to figure this out myself.

Anyone have any ideas on what's going on, or what steps I should take? I'm thinking about checking the PCM ground wires with a test lamp instead of just a multi-meter. Also thinking of checking the voltage on the sensor ground circuit referenced to chassis ground.

I'm attaching the wiring diagram that I got out of the powertrain diagnostics manual.

Thanks for reading, and offering any advice! "In the multitude of counselors there is wisdom!"

Lee

RacerHog

Sounds like it lost the ground. or grounds.... Check for Body to Engine Ground and make sure it has good Continuity...

ScienceMagic

Yeah, it does sound like a grounding problem. A mechanic online said to check the ground to the left rear of the cylinder head. I just can't believe that neither the frame shop nor the dealership would have missed that!
I'll check it this week when I drive down there.
Thanks!

RacerHog

One thing to remember..... The Shop you use is only as good as the tech that is working on your vehicle...
"My motto is" ( If any one of us knew everything, there would be no reason for the rest of us)...
Point being::: Most shops have strong point and weak points in their service they provide.. Careful when shopping for someone to work on you cars.
Hope you find the issue, Keep us posted... Cheers

NOTE:
You are on the right path I think... PCM should be providing the grounds for the circuits. But the rest of the grounds have to be intact so the signal can make it back, and not backfeed from someplace else.

ScienceMagic

Whelp....I drove the 400 miles yesterday to get to the van that was at a dealership. Went in this morning and took off the doghouse. 15 seconds later I found the loose ground wire. There were two wires with ring terminals, held onto the cylinder head with a bolt. The bolt was LOOSE! I pulled it off, shined up the terminals and the engine block, fastened the wires back on, swapped out the replacement, unprogrammed PCM for the one I put in two years ago, and it fired right up! I also put in the pre-programmed PCM from Auto Zone, and it worked too, so I'm just going to keep that one stored in the van in case I ever have a problem again. Takes less than 10 minutes to swap out the PCM, and you only need a Phillips head screwdriver and a 1/2" open end wrench.
Unfortunately, the frame shop routed the shifting cable and two spark plug wires against the exhaust header, which melted it, so now I have to find a new shift cable!

RacerHog

To this day I dont understand why people dont recheck their own work... Just no reason to route things the rite way....
Hope you make the trip home ok in the van?

Keep us posted !!!!! Cheers