Can anyone direct me to a good trouble shooting guide? My son and i are trying to determine why His truck is runing rough. It acts like it is running out of fuel.

 

define rough running and what you have done already.
also what fuel pressure do you have at idle and wot?

and have you pulled codes if so post what they are.

here is VP diagnostic help

http://www.bluechipdiesel.com/vp44diagnostichelp.html

 

Here is a list of what I have done to my truck so far.
I really appreciate your help.
Thank you.


Original problem was a broken fuel level sending unit.



1) Dropped the tank and replaced sending unit.


2) Reinstalled tank and test drove truck. Truck broke down in half a block.
Acting like it is out of fuel


3) Bled each line at the injectors.


4) Checked pressure before and after the fuel filter.

No pressure when truck is running.

18lbs. when I bump the starter.


Took truck to Outlaw Diesel Shop. Here is what he did.


1) Hooked computer up to truck.

Bad injector pump code.

Replaces injector pump.

Starts truck. No fuel pressure

2) Checked pressure before and after filter.

No pressure when running.

18lbs.when pump is priming.

3) Checked voltage to the lift pump while truck is running.

14volts.

Diagnosis is bad lift pump.

Replaces pump.

Still no pressure.
**
4) Retraces my original repair steps.

a) Check quick connect fittings at the tank.

Replaces quick connect fitting at the tank.

Still no fuel pressure.

b) Check fuel line from tank.

Vacume test shows line is good.

5) Eliminates tank and sucks fuel from a gallon jug.

No fuel pressure.


(From step one he is seeing air bubbles in a clear fuel line between the
filter and injector pump)


6) Bipasses filter still have air and bad fuel pressure

7) Replaces fuel line from the tank to the lift pump.

I take my truck home……….. Still broken.

1) Install new draw straw in tank.

2) New fittings at the tank.

3) New fuel line from lift pump to filter.

3) New banjo bolt washers everywhere in the line.

4) Truck runs good for twenty minutes at an idle.

Good fuel pressure. 18lbs when lift pump is priming.

10 to 12lbs when truck is at idle.

***** Does not drop under 6lbs when reved to 3000 rpms.********

*****Truck looses all pressure when I go for a test drive.*****

5) I check my voltage from the ECM to the lift pump. 14 volts at an idle

for a couple of minutes.

***Voltage then drops to zero for a split second and then right back to

14 volts.*****

6) New fuel system relay

7) Went to Atlas and bought an ECM of a 220,000 ml.truck. Motor was running

very well.

Test drove it. Didn't get a block away before I lost fuel pressure.


This is the best we can remember. Hope some one can help.

 

It looks like maybe the ECM is thinking the engine is not running then shuts off the lift pump.or you might have a bad ground or electrical connection causing it to turn off the lift pump. it could also be a bad wire in the loom that is loosing contact from engine vibration. these truck can do strange things You need to go over the wiring real close and make sure all grounds and connections are clean and tight

 

what happens if you "hot "wire the LP, I'm guessing it will stay running? maybe start tracing backwards toward the ecm to see where voltage stops or is intermediant

 

Did you put in an aftermarket lift pump in? This sounds like the samething mine was doing. If it is aftermarket I had to take out the old fuel pump to get mine to quit dying.. but my new problem is that the tank is pressurized and blowing fuel out off the cap.

 

your problem is not likely the fault of a lift pump but that either an injector hold down is loose or one of the copper washers is bad that seals the injector from the combustion chamber.