ALDL is where you connect the scan tool:
Diagnostic codes OBD I - Diesel Place : Chevrolet and GMC Diesel Truck Forums

PMD's are only on 94+ trucks with electronic injection pumps.
93's were mechanical injection only so if you have a PMD please post a picture.
Also the easy way to tell the difference between mechanical and electronic injection pumps is:mechanical IP's have a throttle cable from the peddle to the IP's eklectronic IP's only have wires connected to the throttle peddle and IP.

Also in 2 different replys you have stated the truck is a 93 and a 94,there were big changes between those years so please clear up what year the truck really is or post what the 10th digit of the vin is.

maybe im driving a 93 and a half? i do not have a throttle cable for sure ...ill go out and take another look for this ops ...i looked for it yesterday with a pic of where to look in hand and i didnt see it ..

There is a chance that the engine has been changed out for a newer model short block or complete,in that case the OPS will be much further into the valley under the intake about 1 1/2 inches.

Since you have what appears to be a 94,the LP runs during cranking by the LP relay,and the OPS powers the LP during engine running.
So safely park the truck and put the gear selector into drive and turn the key to run to get the LP to run for testing purposes-the safety neutral switch should prevent the engine from cranking but the LP should run to bleed the filter or whatever.

If that happens you know the LP works and so does the relay.The OPS only activates when the engine is running or you can power the LP directly through the relay by putting 12v to ALDL pin G

Often the PMD fails and causes stalling and no starts but this guide can help diagnose a bad PMD:
http://www.accuratediesel.com/nostart.html
This is not foolproof,replacing the PMD with a know working PMD is the best for diagnosis in the short run for a quick check and every electronic IP owner should carry a spare PMD so a relocation Kit with PMD,resistor,heatsink and extension harness that allows you to mount the PMD outside the engine bay is something that should be had.

tried a good pmd today no luck ..i guess i need to learn how to check my lp..

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ok so i went out to try to fire it up and still nothin ..but i cracked the t valve bleeder and cranked it over and got a lil fuel squirt out ...but now nothin again ...

Not sure how to make this any clearer.

Have a friend put the gear selector in drive and turn the key to start and hold it there,the LP should now be running and pumping.

Open the bleeder valve on top of the fuel filter and bleed out any air in the filter(while your friend holds the key in the start position).

Once the filter has no air and the bleeder is closed,your buddy can let go of the key.

Now crack 1 easy to get to injector high pressure fuel line loose at the injector.Tighten that line back up when the engine starts.

Begin cranking the engine over(with gear selector now in park) in burst of no more than 15 seconds with a 1 minute starter cooldown period between cranking sessions.

The truck should start and run with about 3 cranking sessions if all else is in working order.

If your new PMD is not fastened to the IP or an aluminum heatsink and relocated outside the engine bay with an extension harness you will fry it within about 10 minutes run time.

ok tried that ..no fuel and now a weird friction sound in front of engine

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ok so i tried that and no fuel ..and now there is a weird friction noise when cranking ..

Lift pump relay on the firewall chattering?
Check the LP fuse on the firewall?


Not really sure what you mean by friction sound- a video with good sound posted here might help identify the noise?

sounds like the front by the fan...more of a grind...try to get vid

Idler pulleys,vac pump or AC compressor seizing up?

under the ip? does that make sense?