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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29522
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Need help on my 98 Chevy Silverado with 6.5L Turbo Diesel.

Customer Question

Need help on my 98 Chevy Silverado with 6.5L Turbo Diesel. Having possible fuel issues. Two weeks ago about half way on a 45min trip towing my horse trailer, the truck stuttered/jumped under load. At 1st just once, then a few jumps, then the more I pushed it, the more it shuttered, with a definite loss of power. Once at our destination, I unhooked the horse trailer and drove the truck to dinner. It jumped/shuttered some but not as bad without the trailer. The next morning, drove around to several yard sales for a few hrs with no issues what so ever. The next day, we hooked the trailer back up and headed for home. about half way home, the issue started again and got progressively worse, again. Im an auto mechanic and the best I can describe the issue is if you had a 4cyl gas engine that had 1 plug wire boot arching to ground.

Ive replaced a handful of PMD moduals in the past and this issue seems different. My truck currently has the PMD relocation harness and heat sink located in front of the radiator.

Things I've Done Recently: Pryer to this misfire/shuttering issue, my vacuum pump seemed noisy, so after the shuttering issue I wanted to take a closer look at the vacuum pump. I hooked a vacuum guage to the vacuum line at the waste gate solenoid and only found about 9hg at idle. It would go up to 20hg when I reved the engine. I replaced the vacuum pump and now have 20hg at idle so I do think I had a problem there, but still having the missing issue.

I did some googleing and decided to disconnect the return line near the firewall and connected a clear hose, ran the engine and looked for air bubbles(possibly from leaking fuel lines), no bubbles.

I turned the key on and felt for the lift pump operation, its pumping.

I then moved to the "T" valve up by the oil fill to see if the lift pump was actually pumping fuel. I replaced the black rubber hose from the "T" valve with my clear hose so that I could run the fuel into a clear jar and not all over my driveway. At idle, there is a steady flow of fuel out of the "T" valve, but I noticed some shiney metal flakes swirling around in my clear jar. So I emptied that jar and sprayed out the jar with brake cleaner. I then filled the jar again via the "T" valve, this time only had a few metal flakes.... Repeated and the 3rd jar didn't have any metal flakes. The volumn of fuel from the "T" valve tells me the lift pump is pumping correctly.

Now I pulled out the fuel filter and found more metal flakes in the bottom of the fuel filter housing, and this is where I left off.....

Now for a little history: My PMD moduals have progressively lasted shorter and shorter. Back in about Nov14, I started having the telltale engine shut-offs. The guy I was buying my PMD's from insist that I have an under or over charging issue, or bad ground, ect because he said my modual shouldn't be going bad so fast. So while waiting for another PMD modual, I test alternator output and find that it is a bit on the low side(13.8+-) so I replace the alternator. I also had some fuel seapage around the fuel filter O-ring and when I go to replace the filter, notice quite a bit of metal particles in the housing, and one of the ears broken off the housing causing the fuel filter O-ring to not seat properly.

I go to a diesel repair shop close by to ask why they think I have all those metal flakes in the fuel filter housing. They tell me my injection pump is shot, I need to replace that, replace all injectors, drop and flush the fuel tank, replace lift pump and flush all fuel lines. They said those metal flakes would have made it back to my tank and contaminated the whole system. So at that time(back I Nov14), I got a new fuel filter housing, and while the fuel supply line from the lift pump, I pumped some fuel into a clear jar and had no metal flakes coming from the tank..... Looking at the old fuel filter housing, it looked as though the metal flakes could have been chipping off of the inside of the housing, so I installed the new housing, put in a new fuel filter, and she has ran like a champ until my issue towing the horse trailer two weeks ago??? I still even have a new PMD that I never installed, because after fixing the alternator, the truck didn't have the stalling anymore.

Im at a loss about these metal flakes, and there is so much conflicting info on the web. Delaminating fuel tanks, lift pumps coming apart internally, injection pump issues, oil pressure sensors, ect

FYI, the truck went into the dealer at 50,000 and 98,000 for what they said was injection pump replacements under warranty. I now have 163,000


Submitted: 2 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 2 years ago.
Hello, I'm Cam.
Ne, Your information is great, very detailed.
So looking your issue I am left with 3 possible causes, lift pump, injection pump or injectors. The metal flakes have certainly compromised the injection pump. This is not a PMD issue, that you are correct bout. the PMD issues are stalling issues.
Fuel supply, your lift pump is running. The only spec we need be concerned about is the pressure. IT should deliver 4-7 psi.
So here is what I would like you to test first, see what pressure the lift pump is putting out. Also go to the connector for the lift pump and see if there are traces of fuel in that connector. IF so, the internals of the pump are failing and causing low pressure.
Second, injectors. I suggest taking these out and having them tested. IF any of those metal flakes make it to the injectors, it would cause a flow issue and result in your misfire.
If the injectors test out fine then we are left only with the injection pump itself. I know its not all that old, but these are the weakest link behind the PMD on these engines. IT was so bad that GM had a hotline for dealers and one option was if the pump was replaced recently, meaning there were enough bad pumps sent out.
Check these out and lets see where it takes us.
Customer: replied 2 years ago.
I will check the lift pump pressure. Should I pull all the injectors to have tested, or just a few as a sample test?
Expert:  GM Tech (Cam) replied 2 years ago.
Myself I would do all. Most are easy and most likely bad due to contamination from that junk in the fuel.