ROUGH RUNNING '94 6.5TD

[NOEL_ISAAC]

I have a 94 K3500 6.5TD, it is giving me problems...again. this time my fuel pump was barely pumping, so i changed filter, then drove it to see if that would help. the stupid truck got worse and died on me as i was rolling into AUTOZONE, as the fuel pump burned out on me. i replaced that i my church clothes in parking lot, bleed the air out, and then drove it home. it was stuttering intermittenly, but was alomost normal. after shutting the engine off for a few hours then starting it up again, it would take for ever to even fire. then it ran like pooh, and i had to bleed the air out of the filter again. i have to bleen the filter everytime i go to start it now, and it is still running rough (runs best after bleeding, but gets worse as it is driven).

IVE DONE ALL I KNOW TO DO. REPLACED FUEL FILTER, AND FUEL PUMP...and has 20,000 miles on the injection pump. Could PMD/FSD be causing this problem? if so, this will be my 3rd one, and it is on an FSD Cooler, and it is about 35 degrees here in iowa. However, a few times in the last few weeks my truck just shut off, and it started right back up...which tells me that the PMD is going bad again. i really dont want to spend the $$$ until it gets warmer unless it is the root of my problems. i am going to bleed the injectors tonight, but any other advice would help.

the truck has 184K on it, new heads and injectors @ 155K from dieselautoservices.com...

the only codes that come up are for the transmission, and i have had those for years.

thanks, Noel Isaac

[rjschoolcraft]

It's sucking air from somewhere. Make sure all of your line fittings are tight. I believe that you said you changed the lift pump? Make sure those fittings are tight. From there, just check everything that can allow air into the system.

[john8662]

Also sounds like maybe the lift pump isn't getting the power it needs. You may have a bad Oil Pressure Switch, which powers the lift pump. If your lift pump isn't getting power it will get behind and you will have an air lock like situation. Get access to a volt meter and check the voltage with the truck running at the lift pump power connector. If your above say 11 volts your ok. If your getting like 5 volts or none at all, then you have found your problem. Just something to check, if its hard to bleed all the air out of the system, this is a sign.

Another yet simpler way to check would be to find the fuel drain petcock on the thermostat housing in the engine bay. While the engine is running, open the petcock, if you get and maintain a steady stream of diesel fuel from the outlet hose connecting to the petcock with the engine running your lift pump is working. Otherwise the truck will die. This will make a mess though, so park somewhere over some dirt.

edited for sp stuff, I was a walking zombee all day, sleepy

[ 02-24-2004, 06:13 PM: Message edited by: john8662 ]

[Barry Nave]

What happens when truck is running and you open the water drain vavle?
OPS could be a good check.
FSD, have you read about the screws on the FSD?
Truck should still run good with out the lift pump,under hard pull the injection pump would not have enough fuel to have full power.
When you bleed the filter do you see air first then fuel?

[NOEL_ISAAC]

i am continuously bleeding the air out of the filter (see air bubbles and hear air come out), as well as bleeding the fuel out through the valve. it is almost as if something were sucking the fuel back out of the system....i have checked my fuel cap too. screw it, Im gonna take it to the Pro in Des Moines, Im sick of it. thanks all for your advice though. I appreciate it. keep on truckin'! i may just trade it on a new Duramax, and just not shut it off at the dealership.

[lupey6.5]

been through this about once every 2 years on mine. when you cvrank the motor the lift pump is sent power via ignition system.BUT after the truck starts the power only goes to the lift pump if the oil pressure sens. allows it to even if the ops gauge on the dash seems to be reading right. this is a safety feature that keeps the lift pump from pumping fuel into the engine compartment when oil pressure is lost but ignition may not be(auto accident). you can check two things: the before mentioned-open the air filter bleed valve slightly while the engine is running if it sucks air in instead of pushing fuel out then the lift pump isn't getting it there.THEN hook a simple volt meter to the wires feeding the lift pump and observe the cranking voltage then the running voltage, if the volts drop off after the truck starts then its 99% oil pres.sens./// if the voltage doesn't drop dramatically you may have a clogged tank pick-up screen which requires draining and dropping the tank. NO FUN but i've done it before i was edumacated by an expert.