[MitchUpton]

For the third time now, the ECU/PCM module on my 92 5.2 has failed (no 'Check Engine' light, no connection to OBD-1 scanner, etc.). I drove the original ECU for a couple of years before it failed. Got a refurb'd unit from O'Reilly and it worked great. That one made it less than a week before it died. Put another one in (O'Reilly exchanged for free), and it has now died after only a few months.

What gives? Is it possible there is something with my truck that is killing these refurb units or are they all just so old that it's likely they'll die quickly. I can't have this keep happening.

I may need to consider an aftermarket ECU (or maybe a later Ram truck one?).

Mitch

 

[modelcitizen]

Recommend starting with a thorough charging system test including a check for AC ripple. Need to be certain all power/grounds to PCM are solid with no corrosion in connectors,also verify integrity of complete PCM harness end to end. No chafing,rub thru. Verify injectors resistance in spec. Sometimes refurbed units suffer from quality control issues.
What actually fails on PCM,same thing each time?

 

[ToxicDoc]

Do you have any modifications to the vehicle? any add-on electrical fan? Anything that can cause a voltage surge?

 

[dodge82273]

On the A/c compressor clutch connector , there is a set of diodes , if this is a 3 speed no overdrive , there are diodes in the relay for that , a shorted wot kick out relay for the A/C , and if you installed any aftermarket items with a coil or eletro magnet . Yes the A/C compressor does run in winter , every time you switch to defrost .  any voltage SPIKE that gets back to any computer can / will ruin it sooner or later , jumper cables , battery chargers .. when disconnected/connected ...

 

[MitchUpton]

Ah, now this is interesting. With the suggestion that it might be a loose/frayed connection, I started poking around, just slightly moving wires to look for anything obvious. I happened to turn on the ignition to check that nothing else was out/fried, and the ECU/PCM booted right up!

So, clearly there is some intermittent connection somewhere. Now the trick is to find where. I already need to replace my battery post clamps (they are old and starting to crack). Maybe I'll start there and work outward to make sure the main +/- connections (there are several, 3 off of each clamp) are all in good shape.

Stay tuned.

P.S. I believe this motor was swapped at some point in its life. The wiring does seem 'home grown' in the engine bay (strange things terminated in places), and the EGR has been deleted. I at one point checked the casting number and determined the short block at least looked like a 5.9 instead of a 5.2. However, the top-end is all 5.2 EFI. So, it's sort of a strange beast. Has anyone heard of such a swap before? FYI, it's a pretty peppy motor, and it has always backfired through the exhaust on decel. I'm inclined to believe it has a cam swap and a bunch of overlap or something. No lope at idle though, so I'm not sure what to think there. The ECU/PCM is the 'stock' one though, with code 7141.

Mitch

 

[modelcitizen]

With key on,manipulate harness/connectors at PCM and try to determine as best you can where problem might be.
Try to start engine,if it starts, move wires,wiggle connectors at PCM.
If you can get engine to shut off by manipulating a particular wire/connector,turn key off and investigate wire/connector.
Look closely at pins in PCM/connector to be sure they're not bent or not fully seated or corroded.
It is possible the prior PCMs may not have been bad,a poor/questionable connection  could be the culprit.

 

[dodge82273]

the factory manuals have pictures of all the splice locations in the wiring harness . These factory splices are really "spot" welds , wires are squeezed together and heated electrically , then that joint is taped up , these often fail intermittently over time , then fella's "fix" stuff by running new wires , cutting old ones and leaving them . If you label each connector and to what it goes , you can remove the entire harness , open it up where the splices are , inspect / repair , and re-tape  fairly easily , and much better/neater than while its installed piecemeal . regular ole masking tape , it removes easy afterward ..   

 

[MitchUpton]

I like the idea of pulling the engine harness and really giving it a thorough inspection and rewrap.

I started looking at the way the engine harness sits in the bay today and it's actually resting directly on top of the inner fender well. That doesn't look right. Was there some bracket that held the major bundle of wires (from PCM to fender, tee'ing to engine and firewall) up off the inner fender? Attaching a couple pics to show the current state.

 

[dodge82273]

there is/was just the plastic wrap , and here and there a plastic loop loom attached to a hole in the fenderwell . all loose means someone has been there ...  yeah ounce you tag the connectors , fix whatever is bad , it will lay in there and you'll almost think you didn't need the tags , but .... why not ,  easy enough....  Personally , I used heaver wire for the alternator output , knowing that in production 1/2 of a cent savings on each auto matters to the bean counters .