94 6.5 TD PMD, Strange Issue
 

OK, so my truck is a 1994 6.5TD Z71 with 166k on it and an auto transmission. I've been working through a no start situation the last few weeks. Air/fuel filters are all new, lift pump is good, fuel system is primed w/o any air issues. Ran through the Accurate Diesel no start guide (www.AccurateDiesel.com - PMD Installation Instructions - Accurate Technical Services, LLC) and all checked good until the PMD and IP checks. To continue troubleshooting, I bought one of those $25 PMD's from Pensacola Diesel just to see if a replacement PMD would fix it. Low and behold, she fired right up and purred like a kitten, it was beautiful.... for about 30 mins. Died suddenly just like someone turned the key off, one very small buck and it was dead. The dash lights were on the entire time. Now it will not start or even hit again, just turns over. I'm pretty well certain this issue is connector to the PMD, so I bought a brand new PMD and cooling plate kit with 6' hardness and #9 resistor and installed that certain that this would fix it, unfortunately it did not, still will not even hit while turning over. Before I start over on the progression I wanted to see if anyone has had a similar experience with one of these and what the solution was. Is there an adjacent failure that is common? I'm going to pick up a scan tool and pull codes tonight if there are any and will report back. The truck has been sitting for roughly 3 months if that matters. Any help is greatly appreciated.

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Just checked the codes and got nothing, just 12 repeatedly. Any ideas or thoughts?

Make sure that the IP/PMD harness ground is located on the IP or drivers side battery ground ONLY.

It also does not hurt anything to add a secondary ground from the heatsink to a good engine or battery ground.

Yes sir, that harness is grounded to the little ground screw on top of the IP, clean and tight. I'll add that other ground, I'll try anything at this point!

One thing I didn't note earlier was on that heatsink - the new PMD didn't fit squarely on the predrilled holes on that plate. Because it doesn't align exactly the pmd doesn't sit flat into the plate like it should, there is a small air gap beneath it. I wouldn't think it would really matter, but it may? I will upload a pic to show what I'm talking about.

Here is a pic showing the defect. Poor QC on the plate, two holes are about a 32nd too narrow. Anyway this is the result, and the screws are tight. They were pretty specific in the instructions to tighten at 20-22in lb, impossible with this set up.

That air gap definitely needs to be fixed. It won't transfer heat away from the PMD properly.

The PMD MUST be fit flat and snug to the heatsink(20-25 inch pounds torque on the screws) and needs heat transfer paste or heat transfer pad fit between the haetsink and the PMD.

That gap will cause a very short PMD life-you may even want to send that heatsink back.

Thanks guys, I will call the Pensacola Diesel folks in the morning and see about a swap. They seem like good people, hoping for the best. Gonna try and get that used PMD replaced too, had like 30 day warranty I think. While I'm waiting for these parts to come back, any recommendations on a logical next step? I've been all over the boards and fuel shut off / cps seem to be very common failure. Seems that they would throw a code and I hate to toss money at it blindly... Recommend replacing cps, and if still no start after that try taking that screw out of fuel shutoff (read that in another post)?

I really appreciate the help!

You may want to take a look at the OPS as well. It cuts off power to the lift pump if it doesn't sense oil pressure.

The lift pump is working, but that's a good idea too. This many miles on it, if it isn't bad yet - it probably will be soon! I will knock these three problem children down, hopefully the problem is with one of them

Are the glow plugs working?


Most likely still a PMD issue-if that gap was present for 30 minutes run time the new PMD is probably fried.

Used PMD's are often junk when you get them-it tends to take several attempts and warranty procedures to get a good used PMD.