Interesting 6.5 problem

[phantom309]

I,ve had 5.7's 6.2's and 6.5's,. so i got asked to 'help' you know what that's like right?

Truck is a 95,. the guy tells me it seems to keep running out of fuel,.and he wants to put all new fuel lines and a big spin on filter like i run, so ok .
We replace the fuel tank and sending unit with new parts, and run a dedicated rubber fuel line from tank to pump to engine,. Filled the filter and after 2 20 sec cranks it fires up and runs so nicely!! After about 3-4 minutes it slowly comes down off the faster cold idle a little and then shuts off like you turned the key off. I had a spare pmd with me swapped it and still no fire,. I unplugged temp sensor first,. then checked fuel solenoid, rechecked my spare pmd in my truck,. then verified his original with my truck,.
Turns out that this truck has actually been off the road for about 3 yrs and this is now exactly the same problem as it had when it was parked,.
He tells me that he has gotten it going 2-3 times in 3 yrs and it does same thing,.
The only common things i can see is it supposedly will restart after "time " has gone by,. often with out the batteries in it,.
So,. i,m asking has anybody had to replace an ecm that gives up after it gets 'warm' ? i,m a little stumped here,.

[JohnC]

Maybe a "dumb' question, but, have you verified it isn't simply running out of fuel (at the IP)?

[Yukon6.2]

bad pump,plugged injection pump,
I had a skidder that would act like you described
It ended up being a fitting in the fuel line that was getting plugged.In your case i am thinking in the injection pump.
Each time i would change the filter the plug would dislodge and go back towards the tank.After running for an hour or so it would slowly die like the filter was plugged

[arveetek]

Like has been suggested, verify that you actually have fuel being pumped to the IP.

I had the exact same symptoms on my 6.5L several years ago; I nearly pulled my hair out trying to figure it out. In my case, I was able to determine it was running out of fuel - I still had the factory fuel filter, and I could remove the top of the filter, and see the filter housing was empty. I was able to run the lift pump manually, but no fuel would come from the tank. Give it a few minutes, and it would eventually pump fuel again, but only for a short while. Everything had been replaced - fuel lines, filters, lift pump, fuel pickup. Turns out it was the aftermarket pick up sending unit assembly I had replaced a few months prior. It used an inferior "sock" (screen on the end of the pick up tube) that would slowly collapse shut after pumping fuel and then block the pick up tube, preventing any fuel from getting pumped from the tank to the IP. Let it sit for a little while, and the sock would relax, allowing fuel to start flowing and then the process would start all over again.

I ended up have to scrounge up an OEM "sock" and putting on the end of the pick up tube. Never had a problem since.

Casey

[DmaxMaverick]

OEM fuel filler caps are about 10 bucks. Leaving a bad one loose is free.

[phantom309]

There is no sock i took it off,.i don't believe in them, 5 yrs on my old truck, and 3 yrs now on my burban,.
The lift pump is brand new
There is no fuel cap on it, i told him to ditch it it is an aftermarket locking cap for a gas pot,.
Fired up this morning just fine did the same thing,.
fired up this evening,. same scene,. IT IS NOT a fuel problem,.

Thanks for all your replies.

[Yukon6.2]

One of the many wiring issues my old tow truck with the 6.5 had i resolved at the time with back feeding 12 volts into the harness at some extra solinods it had for wrecker functions.
I replaced the ignition switch and the need for back feeding disappeared.
The truck would just die for no reason randomly,i had a jumper wire from a battery with an alligator clip that i would hook up to the solinoid.It would click and the truck would start.

[More Power]

The gas fuel cap won't work for a 6.5L diesel. It has to be a diesel fuel cap.

Eliminate the oil pressure switch as a potential cause. The electric fuel lift pump in 1994-95 models is powered only by the oil pressure switch when the ignition key is not in the "crank" position and at least 7-psi of oil pressure is present. A typical 6.5 will run without an operational lift pump if there isn't some other problem, like an air leak in a fuel line or partially plugged fuel filter.

Next, monitor the voltage to the FSO (Fuel Shut-Off) solenoid on top of the fuel injection pump. A rough test is to wrap your hand around the vertical solenoid and cycle the ignition key from off-run a couple of times when it won't start. You should be able to hear/feel the solenoid activate. This not only tests the solenoid but also the ignition circuit.