Hopefully you guys can help me catch this little gremlin.


Symptoms
Once the engine has been running for 20-30 minutes, and the engine sees more than 2500 rpm (moderate acceleration), it starts to stall and run rough. Sometimes it cuts off and takes 10 or more seconds to restart. Idles fine, and when driven easy (less than 2K rpm) it runs okay.


Remedy attempts:
1. Cleaned battery terminals and grounds thoroughly
2. Replaced Fuel Filter (the new one is not a GM filter)
3. Installed new factory air filter AC1300
4. Replaced Oil Pressure Switch
5. Previous owner (my Dad), said he just replaced the Lift Pump (I can hear it running during Wait to Start: It looks new)
6. Checked for frayed wiring (found one frayed spot on the Glow Plug thingy behind the Turbo Power cover: The cover looks to have worn off the red insulation: wire OK)
7. The fuel tank sender unit has been replaced recently (fuel gauge jumps around erratically: Was told a competent mechanic replaced it and compared the old vs new before installation: noticed connector is covered in dried mud)
8. Replaced gray Stanadyne PMD (located beside fuse box in the engine bay on aluminum cooler)
9. Relocated the new Stanadyne PMD/cooler to the bumper opening with the fins facing oncoming air: reused #9 resistor off old unit)
10. Inspected diesel fuel tank cap (it says diesel fuel only, there is a slight hiss when opening sometimes: tried driving with it off to no avail)
11. Checked for Water in Fuel (none)


Other recent maintenance items:
1. Replaced 4L80 fluid/filter
2. Checked all drivetrain fluids/greased fittings
3. Removed Directed Electronics Remote Start System model# 552T
4. Add diesel fuel supplement per fill
5. New seals in oil filter adapter (was leaking)
6. Cleaned the engine compartment with degreaser.


Notes:
There is oil in the intake track. Some parts of the ribbing has pooled oil.
MAF sensor definitely has been cleaner, but I don't want to bother those resistors if not necessary.
Lift pump seems to be working while engine is at idle, but the whole truck is shaking, can't tell if it is actually running. It definitely works on start up though.
Ignition switch is hard to turn sometimes, and is showing its age.
One day it was stalling everytime I went over 2500 RPM, so when I got it home I put the vehicle in park with no load, revved it up to 2500 RPM and it died after a couple seconds.
The wiring harness is greasy and dirty. Some of the weather locks have broken off due to brittle plastic. Well, the whole engine is greasy and dirty below the valve covers.


Any help would be appreciated.

 

Finally got it fixed. Thought I had it fixed three other times. We will see how long this lasts before disappointment sets in. I have learned not to get my hopes up.


I was cleaning random electrical connections and noticed a group of about five connectors below the hydraulic brake system on the driver's side. Lo and behold the connector was full of what appeared to be hydraulic fluid. Upon closer inspection, at least three connectors below the brake system were drenched in fluid. It had seeped past the weather connector seals somehow. One of those connectors went to the lift pump. There is evidence of a significant, extended fluid leak under the driver's side.


I thought for sure that was the problem and the gremlin was dead. Then 20 minutes into the test run, right after topping off the tank, she died on me again. This time she took a while to crank and I couldn't hear the lift pump at all during Wait to Start.


She limped home and the next day I launched Operation Straight Wire. I put a big 30 amp switch in the driver's side kick panel and ran a 10 ga wire to the lift pump. I found the ground wire on the lift pump (black) and noticed it went towards the rear of the truck? Never could find where it was grounded, so I made a new ground in an easy to work on location. And just like that I had complete control of the lift pump. FYI, it uses 14 ga wiring for the pump, 10 ga is overkill. I ran power from the fuse box and used one of the two 30 amp accessory ports.


During the test run it ran terrible, stumbling, farting, smoking, no power, but it DIDN'T STALL. I got back and revved it a couple times with no load and she was definitely 'missing.' I popped the hood and started looking around.


I turned on the lift pump and unscrewed the filter bleed until diesel spewed. There was quite a bit of air trapped inside. Restarted and revved a couple more times, still missing.


Then I noticed one of the glow plug wires I cleaned was just dangling. DOH


I also reinstalled the old Stanadyne PMD.


It started running right. I cautiously took her for a little spin. After getting down on it a couple times without stalling or stumbling I think it is safe to drive. (drove for about 30 min)


Some notes:
Use 12 or 14 ga wiring for stock lift pump straight wire
For firewall hole use a rubber grommet
Make sure you have at least three 30 amp fuses, two for the accessory ports, and one spare (there is a spot for the spare in the fuse box)
Make your own trusted ground
Top of the driver's side kick panel is a good spot for the switch, especially if you have kids that would love to play with it
Remove the 30A accessory fuses and the courtesy light fuse during work


Could it be the new Stanadyne unit was junk? Only bought it to have a spare.

 

I think you found the trouble and missed it.

You have air getting in the fuel somewhere between the fuel level and the LP.

 

I agree with racer55.. air leak, likely instigated by an intermittent, inop or faulty LP.. Assuming the new fuel sender's fuel strainer was the correct one. Common knowledge that nearly all aftermarket replacement diesel fuel senders are shipped with the incorrect gasoline fuel strainers that significantly restrict fuel flow, specially in high demand and/or cold weather operations.

A clogged or restricted fuel strainer will cause the lift pump to work that much harder and hotter, eventually failing. As the lift pump begins to overwork and overheat, it starts drawing more amps further stressing the underrated OPS switch and so goes the frequent failure rates.

An inop/faulty LP for what ever reason, will often expose air leaks that otherwise wouldnt exist.... Unfortunitely, once exposed, they dont typically disappear after the fuel system pressure is restored (LP fixed) and can cause havoc when parked for extended periods (ie fuel system loses prime).

Air leaks are not always pre-lift pump, and many post LP air leaks dont leak fuel, most dont even exhibit wet spots to indicate a breach.. If it were only that easy..


FWIW. Proper lift pump replacement procedure includes dropping, inspecting and cleaning the fuel tank if necessary. Removing, cleaning, inspecting and testing the fuel sender, and replacing the fuel strainer.. Unlike our gasoline counterparts, our lift pumps are conveniently mounted on the frame, outside the fuel tank so most PRO's and DIYrs dont bother following PROPER PROCEDURE until its cost em a few OPS and/or OEM lift pumps if not a high dollar lift pump or two also..

If your not 110% positive your new fuel sender was fitted with the proper fuel strainer, that would be my FIRST suspect... See attached...

Also, if your fuel filter is made of black plastic w/ molded retention nut, that would be my 2nd suspect. I strongly suggest the metal tops w/ seperate element retention nut, the one pc black plastic molded pos is prone to leaking (losing prime when parked for extended periods)... See attached...

 

You guys are right. I thought it was fixed until after driving about 45 min at freeway speed it started to stumble and shut off. I almost didn't make it back home. I ended up swapping PMD's in and out and sitting beside the road quite a bit while my wife looked on. Thankfully she was following me to pick up a load of dirt. Holy moly that was disastrous, the thing shut off on me at least 15 times, and I am afraid it cooked both my PMD's.


Unscrewed the Fuel filter housing and turned on the lift pump to get a look at the flow, it barely was working. Fuel was pulsating out, but it was more of a leak than impressive pressure. LIFT PUMP IS FRIED. Also noted it was a Precision lift pump, not ACDELCO.


Also, the Filter housing had quite a bit of sand and debris in the warmer filter area. I also had just installed the black plastic top filter recently (don't know if I mentioned that)


What I have ordered:
EP309 lift pump
OEM Fuel Separator (comes with new filter)


My Dad did have a new sender unit installed in the tank. He didn't do that one himself, and the mech told him that he compared the two units side by side. Sounds to me like the fuel strainer MUST be checked now.


What a pain, as I just topped off the thing. That tank must weigh 500 lbs!!

 

Oh yeah, and I got a one year warranty on the PMD I just bought, sending it back for a new one.


I will be checking the strainer in the meantime. I will let you guys know the results.


Thank you for help.

 

Update:
Installed a new lift pump (OReillys replaced the Precision pump for free). Noticed the O ring was missing from the fuel line (tank side of the lift pump)


Installed a new OEM fuel filter housing (came with metal top filter)


Installed the old PMD and took it for a spin (new one will not be in for a week)


Result:
Started shutting off repeatedly after about 30-45 min. Wait a bit, starts right up. Limped home. Glad I don't go far!


Tried to get the part number for the strainer with no luck. The mech would only say he was sure he ordered the right part.


Also the ACDelco lift pump came in. Should I use it instead of the new Precision pump?


I was tempted to run them BOTH!

 

pm sent. let us know what you find..

 

It was the fuel sock. Took it off and she ran for hours...with the old Stanadyne PMD installed.

 

imagine that... If you didnt replace the strainer, dont let the fuel level drop below 1/4 tank (last 4-5 gallons of fuel). As the fuel sloushes 'round, it could expose the pick up tube to atmosphere and inject a big gulp of air into the fuel system.. The pick-up tube does NOT reach the bottom of the fuel tank. Its raised up an inch or two and the fuel strainer acting like a wick draws the fuel from the bottom of the tank.


As for it working with the old PMD, common.. Ghost of Mr GoodWrench mistaken as just another passing PMD goblin...

Glad you got it fixed..