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6.5TD dies after running awhile, especially when slowing down or after running and idling

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Cattapper

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So I bought this 96 GMC 3500 4x4 single wheel 6.5TD with 87,000 miles on it. Great truck, great condition. However it had sat awhile and had stale fuel in it. I did all the obvious things like new fuel, injection cleaner, fuel filter {twice}. It was new to me so when it started cutting out i thought it was the fuel but turned out to be the PMD. I relocated it and it ran great for about 500 miles. Then it started this random dieing. Sometimes you just need to recycle the pump and it starts up, other times wait a couple minutes and then it starts. If not I get out open T valve and cycle the pump a few times and close. It then starts. So i thought it was a fuel or fuel component so i started at the tank and worked forward. Here is what i have done and im still getting this issue.

1-Replaced Fuel sending unit and sock
2-Replaced Frame pump
3-Replaced Fuel relay module
4-Replaced Oil Pressure Switch
5-Replaced the Sensor right ontop engine by PMD harness. Cant rember name
I keep coming to the conclusion that its getting a air lock or air in the line and kills it. when it dies it doesn't cut out, it just dies!!

Any help very much appreciated
 
Welcome @Cattapper first line of diagnosing is the clear line like Ak said. then we move on to checking fuel pressure at the IP inlet in front of the fuel filter. the line is a 1/4" and you can pick up a 10' roll at the hardware store. it does not have to be rated for fuel. most of us run that same hose and it will last a couple of years until it starts turning dark.

when you relocated the PMD, did you replace it with a new one or re-use the old one? If new, did you remove the resistor inside the PMD connector and install into the new one?

If you just relocated it and still running the old one, it's possible the old PMD is the issue, but check for air first in the return line.
 
dbrannon79 said:
Welcome @Cattapper first line of diagnosing is the clear line like Ak said. then we move on to checking fuel pressure at the IP inlet in front of the fuel filter. the line is a 1/4" and you can pick up a 10' roll at the hardware store. it does not have to be rated for fuel. most of us run that same hose and it will last a couple of years until it starts turning dark.

when you relocated the PMD, did you replace it with a new one or re-use the old one? If new, did you remove the resistor inside the PMD connector and install into the new one?

If you just relocated it and still running the old one, it's possible the old PMD is the issue, but check for air first in the return line.
Click to expand...
I did replace the PMD with new one and it came with the a resister. I tried to get the old one out but it was very tight and i didn't want to break it. I just plugged it in to see if it ran. It did and was not jerky anymore. I will revisit this again tomorrow when in working on the truck.
 
Cattapper said:
I did replace the PMD with new one and it came with the a resister. I tried to get the old one out but it was very tight and i didn't want to break it. I just plugged it in to see if it ran. It did and was not jerky anymore. I will revisit this again tomorrow when in working on the truck.
Click to expand...
I had a problem with my truck running jerky and doing all sorts of weird 💩.
Plugged in the other PMD and it then run perfectly fine.
I had a spare resistor so removed the resistor from the rough running PMD, plugged in the spare resistor, switched back over to what was the rough running PMD and it then run perfectly fine and normal.
So with that I learned a lessen. If a PMD is causing the engine to run rough and doing weird things, try first changing the resistor before condemnng the Pump driver.
After moving the driver to behind the front bumper, I now just call it the pump driver, or the FBMD. Front bumper mounted driver. 😹😹😹
 
Confirm the advice on fuel pressure at the Fuel Filter manager. A quick and dirty way is to use an inexpensive pressure/ vacuum gauge. Replace the hose with a long enough length of 1/4” line to run from the T-Valve and up to the windshield. Tape the gauge securely to the windshield so you can monitor what’s going on while driving. Return and report results.


To give you an idea on the clear line, BigT just posted a great video of his clear fuel line diagnostics (he had a return line leaking down. After he found the issue, the fuel remained in the line with only a small bubble at the top of the loop (normal). It’s normal to have some bubbles but, a lot or continuous…not so much.
 
Yeah most of us just eliminate them and run a pre-filter somewhere before the LP. I opted to add an inline one, then later when I replaced the LP (lift pump or frame pump) with a facet that has it's own 50 micron screen and bowl, eliminated the inline filter too.
 
I will preform the air test and see where im at. Im also really leaning back to bad PMD. When i ordered the relocation kit it came with harness and grey stanadyne pmd. Ive read mixed things about them. So i went to parts store and got a Doorman PMD. However Im not able to hook it up as the connection is different than my harness now. Always someting.
 
Cattapper said:
I will preform the air test and see where im at. Im also really leaning back to bad PMD. When i ordered the relocation kit it came with harness and grey stanadyne pmd. Ive read mixed things about them. So i went to parts store and got a Doorman PMD. However Im not able to hook it up as the connection is different than my harness now. Always someting.
Click to expand...
If I remember right. With a little filing and a pocket knife, they can be connected
 
Yes there is a TSB out there somewhere from GM that states a new design on the connector where you have to file or trim the male end to make it work.
 
Item# 300 where they made something not interchange so they could track ifthe change made the correction. (Hint: it didn’t).

Is the one you bought lifetime warranty? If not return it and buy one from Leroydiesel.com.
Having a ready to go spare on hand is a simple requirement of owning this ds4 6.5.

Drive on the lifetime warranty unit. When a problem occurs, swap to the backup and ship out your warranty unit for replacement. When it comes back run on it again and keep the non warranty unit as the backup.

My suggestion is have a second heat sink with the second pmd mounted ext to the first (or both on one large heat sink). Put a dummy plug into the spare pmd to keep it clean. When a problem pops up, just move the wire and you know instantly if that was it. A fast repair when in bad weather or dangerous location easily makes the effort worthwhile. Then remove that bad one later at home when convenient to ship off for warranty.
 
Cattapper said:
… I just plugged [the new PMD] in to see if it ran. It did and was not jerky anymore….
Click to expand...
Can we assume correctly that by ‘just plugged it in to see if it ran’ you mean you had the new PMD mounted on to a heat sink the whole time you were testing it to see if it ran? Just making sure.
 
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