hard to start after 80 or 90 miles drive
 

Gmc 99, 6.5, with relocated PMD, after driving a good distance becomes hard to start. Once it does, drives back OK. What could it be? Changed PMD a few months back, as well as fuel filter, fuel pump injector(under drivers side) it's increasing hard to start. It cranks and cranks as if no fuel was flowing thru. It only does this after a long hot drive. Any suggestions? dont know of any codes. It has over 220k miles, sems if i shift from park to drive before turning the key on got it started once. Thanks

Try pouring water on injection pump next time it wont start,if it starts your pump is on it's way out.

sounds like the IP, i had the same issue with my old trk it did the same thing after my ops went bad.

hard to start after long drive
 

Could you tell me what the IP is diesel head and how to change it

IP is your injection pump, its not cheap or easy to change. As Mase said next time it does not start try pouring water on it to cool it down and see if it starts, also check to see if your lift pump in the frame rail is actually working, it works off of the oil pressure sensor and that circuit often fails which starves the IP for fuel and eventually makes it go bad.

On a 99 the OPS is only a back up power supply.
The ECM controls LP operation at all times through the LP relay on 96+ trucks.
the only time the OPS should be noticed activating the LP is after engine shutdown while oil pressure bleeds off-the LP continues to run for a few seconds.

The advise is great as the LP should be operational and able to move a good volume and pressure of fuel though-if replacement of the LP is required AC Delco EP158
DELPHI Part # HFP905

update, on hard to start gmc
 

Well, I changed the electric fuel pump, drove it awhile. Parked it. Waited about 30 minutes and it is still hard to start. Tried it several more times and it starts. So the problem still exists. It is frustrating, but, what else can I do?

hard to start.
 

What is LP ? What does it stand for?

LP is short for lift pump. It's the same thing as the electric fuel pump your talking about. To test it open the t - valve at the front of your engine or unscrew the plug at the top of the filter (with the engine running) You will get steady flow of fuel coming out if the LP is working properly.

To add if the truck stalls the lift pump is not working for some reason yet to be determined.