Hey Ferm

Skools Out · #1 11-20-2011, 11:46 PM

Hey have a question what would cause my diesel to die like it's running out of fuel? i replaces the fuel shut off on the pump didn't fix it. the pump was replaced about 2500 miles ago. the other night i drove it out and run fine i cut it off went in came out wouldn't start i purged the fuel system and it cranked for a sec or 2 then wouldn't start. towed home and then it cranked right up now can't kill it. ugh what ya think?

THEFERMANATOR · #2 11-21-2011, 12:15 AM

Sounds like a bad PMD/FSD to me. If it is still mountred on the pump or on top of teh intake then it is suspect as to being bad. Even mounting them outside the engine bay isn't a guarantee they will last, but it sure seems to help. I know they can cause all kinds of problems when they go out though.

Skools Out · #3 11-21-2011, 12:23 AM

sorry should have saved ya thoughts on that, have new one mounted outside engine area when it acted up first thing i did was go to my back up i have under the hood on a cooler and same problem. so it's not that...

THEFERMANATOR · #4 11-21-2011, 12:29 AM

What year? Is the fuel pump working?

Skools Out · #5 11-21-2011, 12:34 AM

1994 with newest avail pump from Heath Diesel. the lift pump is making noise and when i turn the key it pumps out the top of the filter if i open the primer cap. it didn't start acting up till it sat and with the new pump. when i get home i was going to replace the fuel filter first and when i opened the primer petcock on top of the water neck for the pump i never got fuel thru the pump.

THEFERMANATOR · #6 11-21-2011, 12:49 AM

On a 94 the fuel pump runs either by the oil pressure switch once the engine is running, or by the relay which is triggerred by the ignition switch start circuit. The oil pressure switches are a known issue for 95 and older GM diesels as they run the entire fuel pump load through the oil pressure switch and burn out pretty often. Most wire them to run all the time when the key is on, or install a relay inline to carry the load and use the oil pressure switch to trigger the relay. If the pump works when you hit the key, but you don't get fuel while it is running then most likely your oil pressure switch is bad. Only use an ACDELCO replacement as the aftermarkets will cause you to pull your hair out. No fuel presssure while running can cause all kinds of problems, and also take out your injection pump.

Skools Out · #7 11-21-2011, 12:53 AM

ok will replace the oil pressure switch when i get home the oil pressure switch is original it has 230,000 miles on it. what do ya mean take out the pump? you mean replace again?

THEFERMANATOR · #8 11-21-2011, 01:07 AM

Quote:

Originally Posted by Skools Out

ok will replace the oil pressure switch when i get home the oil pressure switch is original it has 230,000 miles on it. what do ya mean take out the pump? you mean replace again?

The DS-4 injection pump doesn't like to run hot as it is cooled by the fuel flowing through it as well as lubricated by it as well. They really need a minumum of 2PSI at all times to make them live and function properly. When teh lift pump fails it causees it to run under vacuum and can cause teh injection pump to fail as it will eat up the internal seals. Normally it took out the PMD/FSD before any pump damage occurred though in a stock application. Also pin F of the ALDL plug can be jumpered to 12V+ and make the lift pump run for testing purposes, or you can check it for power while it is running to see if the pump is getting power.

The pic is upside down.

Skools Out · #9 11-21-2011, 01:11 AM

it's only done this twice to me. but you know last time when it wouldn't restart i don't remember hearing the lift pump when i first turned on the key but when it did start i heard it. hum maybe it's just a bad lift pump. it is original lift pump too.