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Discussion Starter #1
Bought this truck 3 years ago and replaced the lift pump before I could even drive it home because it would run a few minutes, die, and wouldn't restart. Managed to drive it home 100 miles after that but parked it because of a transmission problem.

Fast forward 3 years and I think I fixed the transmission issue, bad TCM, and went for a test drive. a half mile down the road the engine quits. Cranks fine but no start, so I roll onto a parking lot and walk back to get some tools. I disconnect the fuel lift pump and put 12 volts directly to it from a jump box. I can hear it working so I get in the truck and it starts up fine, and also notice the water in fuel light on for the first time. Reconnect the fuel lift pump and manage to drive it back.

Any ideas why the pump isn't getting power periodically? I've started up the truck a dozen times in the past few years and let it run 10 minutes with no problem. The last 2 times it's quit like this time, but if I leave it and try a week later, it starts right up?
 

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Could be quite a few things.

The lift pump gets power from the Oil Pressure Sensor and the relay inside goes bad, the gauge will still work but won't supply power to the LP. Search the OPS relay mod. If you don't do the mod, at least replace the OPS with an AC Delco only.

Also, check ALL of your fuel lines for air leaks and it would be good advice to drop the tank and either replace or completely remove the pickup sock.
 

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Discussion Starter #3 (Edited)
Yes the oil pressure gauge does work. I also replaced the fuel filter above the IP when I replaced the lift pump. OK I'll replace the OPS as it's cheap. Is the fuel pump relay known to go bad? That's pretty cheap to and would eliminate 2 unknowns in the circuit, even though I hate to just throw parts at a problem. Would the truck even run at all if these were bad, or is it an intermittent situation?
 

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Intermittent power.... check grounds. Pull the black lift pump ground wire out and find where it is grounded to the frame... and likely you will find issues. This is how I fixed mine...
 

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Yes the oil pressure gauge does work. I also replaced the fuel filter above the IP when I replaced the lift pump. OK I'll replace the OPS as it's cheap. Is the fuel pump relay known to go bad? That's pretty cheap to and would eliminate 2 unknowns in the circuit, even though I hate to just throw parts at a problem. Would the truck even run at all if these were bad, or is it an intermittent situation?
Good idea to do the LP relay mod with all new items so you know where you stand with those. Letting the truck sit for a long time is an open invitation to vermin nesting and chewing on wire insulation. With the intermittent nature of the problem I'd do a VERY close inspection of the wiring and even run some new ones if in doubt. ~FH
 

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Discussion Starter #8
Just getting back to the truck now. I powered the lift pump directly by a jumper wire in the relay connector. It ran fine in the parking lot for 10 minutes idling, then I drive out to the street and it quits. Crank and no start. Got it started after about the 5th try. Drove it back in and it quits again, feels like it runs out of fuel. Idles a little rough then dies. Got it started again and parked it. What else to check? When it runs, it runs great, nice and smooth. I see in the wiring diagram a fuel shut off valve. If I remove the pink wire while the engine is running it quits immediately. Any problems with that valve?
 

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Just getting back to the truck now. I powered the lift pump directly by a jumper wire in the relay connector.
What relay connector?

It ran fine in the parking lot for 10 minutes idling, then I drive out to the street and it quits. Crank and no start. Got it started after about the 5th try. Drove it back in and it quits again, feels like it runs out of fuel. Idles a little rough then dies. Got it started again and parked it. What else to check? When it runs, it runs great, nice and smooth.
Did you replace the Oil Pressure Switch with an AC Delco D1808A? If you replaced it with an off brand you wasted your money. Put an AC Delco OPS in.

Did you do the OPS Relay Mod: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/268296-ops-relay-install.html?

Do you have a diesel rated fuel cap? If you are not sure, then get a new one. Stant 10591D for example.

Until you can pass the lift pump test (explained here: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/39350-reference-material-lift-pump-ops.html) you will continue to have fuel flow problems.

I see in the wiring diagram a fuel shut off valve. If I remove the pink wire while the engine is running it quits immediately. Any problems with that valve?
The Fuel Shut Off Solenoid must be powered or fuel is shut off to the Injection Pump. That is why the engine stopped when you disconnected the pink wire.
 

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I'm not seeing where you've determined that the lift pump is not getting power when the engine stops running. Have you? Are you sure it's not still running but not pumping fuel?
 

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Discussion Starter #11
What relay connector?
The fuel pump relay connector on the firewall.

Did you replace the Oil Pressure Switch with an AC Delco D1808A? If you replaced it with an off brand you wasted your money. Put an AC Delco OPS in.

Did you do the OPS Relay Mod
Not yet but for testing purposes, the jumper wire in the relay connector as mentioned above bypasses the OPS and runs the pump directly.

Do you have a diesel rated fuel cap? If you are not sure, then get a new one. Stant 10591D for example.
I has dual fuel tanks and the factory tank has a standard ratcheting cap and the aftermarket tank uses a simple screw on cap. I'll check the rating.

Until you can pass the lift pump test (explained here: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/39350-reference-material-lift-pump-ops.html) you will continue to have fuel flow problems.
I will try opening the valve to check fuel flow the next time it dies.

The Fuel Shut Off Solenoid must be powered or fuel is shut off to the Injection Pump. That is why the engine stopped when you disconnected the pink wire.
I meant does the solenoid go bad very often to cause problems like this?
 

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Discussion Starter #12
I'm not seeing where you've determined that the lift pump is not getting power when the engine stops running. Have you? Are you sure it's not still running but not pumping fuel?
Good point. Is that where opening the valve at the front of the engine will check it while the pump is running?
 

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Yes, perhaps. I was thinking of putting a test light on the pump to test the presence of 12 volts. On a 92, the pump only activates with oil pressure (later years they activated with the key even without oil pressure).
 

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Good point. Is that where opening the valve at the front of the engine will check it while the pump is running?
With the engine running, open the T valve. Make sure to have some rubber hose on the drain and use something to catch the fuel.

Fuel should come out in a steady stream.

If the engine stops running after 30 seconds or so, the lift pump is not working or it is not getting power to make it work.
 

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Discussion Starter #15
With the engine running, open the T valve. Make sure to have some rubber hose on the drain and use something to catch the fuel.
Looks like it's been over a year since I worked on this truck so it's time to try again. Been starting it up every few months since then. It may run just fine for 10 or 15 minutes before I shut it off, or it may run 30 seconds and die, won't start again. Got a pair of new batteries as a first step. Have a theory from searching on-line that the sock in the tank sender is collapsing after a little while and cutting off the fuel supply, so the first thing I want to do is connect a fuel pressure tester. Can I attach it to the hose coming from the t-valve? I got the fuel pump hotwired so if the engine dies, the pump will still be running so I can monitor the pressure. BTW, should it matter that I have 5 year old diesel in the tank, more than half full? Since it runs fine when it actually runs, I wouldn't think that is an issue. I did add some 911 to the tank 2 years ago.
 

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I go one step further on the battery bolt upgrade...

I use 2" SS bolts, and TWO nuts each terminal... one to tighten the cable to the battery, and one to LOCK the first one in place!:bigglasse
 

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Looks like something are growing in there.
 

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Looks like rust, plain and simple to me... Either way, it's due a cleaning...
 
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