Been having this issue for quite some time (3 years), been through all these post about the same stuff and short of replacing the damn IP, I have: replaced and relocated PMD, replaced LP, replaced OPS, unplugged the IP OS (no start).

So I have been lead back to the fuel relay. What is it's function, as when I attempt to turn it over (without it instatlled) it still runs the LP, and does just about everything normal. But when I bench test it the coil ohms out to about 57 ohms and the normally closed contacts read short but when I put 12vdc to the coil the NC contacts remain shorted and the NO contacts remain open... ok so that tells me it's bad, but what it is normal function and why would the truck run normally except for the random chugging that a failed PMD would normally give me? Thanks in advance

94 3/4 ton suburban 6.5l TD

 

yes PMD give you that clugging i have seen it many times just because new don't mean not going going on you you said your relocated where did you relocate to if the front good you may want ohm test cable make sure it not shorting out also is PMD still gorund to IP and check all the ground and clean the ground to the puters are at the back of motor on right side intake and there should be ground straps also right bolted to firewall under a/c dryer one to motor and other to the frame

 

PMD is located up under the bumper next to license plate in knock out for flood lights. Get's good airflow there so I figured, sure. Checked the extension all wires good. Checked ground for IP good now... check 1 ground on passenger intake. now good and both battery, now good. have to wait for snow to melt before I can check the others. Not keen on on laying in a snow bank to check it. But as soon as I can move it, will do. Back to my original question, though, What does the Fuel Relay functionally do? You have tons of experience with this stuff so I am glad you responded. Thanks for any and all help Crazy.

 

If i had read right the relay only activates lp during cranking, ops takes over after it starts

 

About the lift pump relay:Looking at the wire side of the relay with the latch facing up, the coil is the 2 narrow pins. The broad, offset pin is common.

with 12 volts to the coil: the broad right pin is open; the broad left pin is closed. The opposite readings when the power is off.

In the '94 6.5td I understand that the lp relay is only actuated during the start cycle so I doubt if it is the cause of your running prob. I had the same rough running problem along with wouldn't start hot and a few more aggravations which were all solved with a new pmd and relocation.

 

What is a pmd

 

PMD is what runs the IP system