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PMD replacement, now no fuel...

The OPS is bad as mentioned, that's why the LP only pumps with 12v jumped to it.
Where is the FSD remote mounted? If the extension is from Edam in Quebec both it and the PMD are suspect.

Leo
 
x2 on the OPS, it is a 95, so OPS is needed for LP during run.

The challenge is we don't how long the OPS has been bad causing the LP not to run. Try to replace the OPS first with ACDelco OPS. See if it can start. In a no start condition because of non working LP/OPS, you need to get the air out from the fuel system first.
 
Problem still exist with LP jumped.

IF it were my truck i'd get real time fuel pressure with LP jumped just to verify you have proper fuel pressure when vehicle dies via gauge.
If you do have proper fuel pressure verified with gauge, then you can rule out LP/fuel pressure, and deal with teh OPS issue after.


Does it always die exactly 30 seconds? or sometimes 10, sometimes 1 minute, sometimes 30?
 
explain how you know LP is not running? In 95 it wont run with just IGN on, so are you actually checking it when LP should be powered in a 95?

In 95 you should be able to put truck in gear and turn key to START and LP should run. Verify this. Then put a multimeter to pin G (bottom left) of OBD1 port and fire truck up, if you dont see 14V there as soon as truck starts then OPS is bad. Check the fuel pressure at the T-valve drain while truck is idling (that 30 seconds or so).

Sounds to me that you have an air leak into the fuel. Unplug the Optical Sensor (black stubby connector on top of IP) and it will probably run without dying, except be in limp mode.

Are you at least getting DTC12 when you check codes?
 
also checking voltage and even pressure of LP (idle and drive) still leaves open the question of volume if i am correct. The LP can have 12V and good pressure (as in my case) and still not deliver the volume due to an air leak (link to pics of rusted fuel lines on top of tank now).

just another thought. the leak can come from anywhere between IP and Fuel Sending Unit.
 
The lift pump did not energize with the key on or in start. I jumped it to 12v and got fuel from the t-valve. The owner had checked fuel pressure and only saw 3psi. I'll verify that next time I'm there.

Can I just put the gauge on the t-valve?

I will check for and fix any fuel or air leaks in the fuel system. and report back.

Does the OPS do anything other than run the LP?

The truck dies at aproximatly 30 seconds, not exactly and sometimes it will run long enough to move it a short distance, but never runs for any real length of time.

What is a good fuel pressure with LP on and truck off? Truck at idle?

Thanks for all the info. I'll be checking on all this stuff asap.

Bill
 
Yes, you can put gauge on the t-valve. Idle pressure should be >7 psi. WOT >4 psi. So it can be both LP and OPS.

OPS also sends signal the the Oil Pressure Gauge, so it has 2 separate functionality.
 
JMJNet said:
Yes, you can put gauge on the t-valve. Idle pressure should be >7 psi. WOT >4 psi. So it can be both LP and OPS.

OPS also sends signal the the Oil Pressure Gauge, so it has 2 separate functionality.
Click to expand...

To cause the vehicle to die it would have to read zero or close to it. The IP will suck on its own too, so it may read a negative value before it dies.

Also helps to see if it holds pressure at turn off. If it does, that would eliminate air leak possibility i would think.
 
Look to make sure your LP fuse isnt broken. Thats more likely, otherwise you also have a broken LP relay. Or the Crank fuse. My 94 is a little different, but I have a pre (Crank fuse) and post (LP fuse) LP relay fuses.
 
Ok, I unplugged the Optical Sensor and the truck didn't stall. :) The lift pump definatly isn't working and the fuses are fine so I am assuming the OPS is bad. I told the owner to replace it with one he has on a different engine, or to just go buy a new one. I could tell there was a leak by the filter and was told that the owner has a new filter so I told him to replace the filter and check for leaks. Finally, could it be the Optic Sensor itself? Is the optic sensor picking up air bubbles in the fuel or what? :S The owner is pretty happy at this point because the truck hadn't run for that lenth of time in like 6 months.

Thanks for any help...

Bill
 
The best way to check the LP is to jump it to override the OPS. So if the LP is also bad, then you know it. Also, make sure he puts ACDelco OPS not other brand.

Leak from fuel filter usually caused by not seating the filter properly or the old o-ring is still there. Trouble is once it is tightened up, the o-ring deformed and will not seal anymore. Needless to say, he needs a new filter since you cannot get just the o-ring. Happened to me.
 
Advise the person to also change the relay for the LP, that powers it when the IGN is in the start position.

The Optical Sensor might just be seeing air and killing the engine.
 
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