Won't Stay Running?

[88fordidi]

Alright, so I've been struggling with my truck for the better part of 3 weeks now. (My truck is 88 7.3 with banks non-wg, 5spd 4x4)

The problem first occurred while I was driving, I was just about to the floor at about 2700 RPMs when suddenly I dropped power. The truck kept running though, and as I was pulling in about a mile up the road it died going down the drive. I popped the clutch and it started back up long enough to get it parked and I shut it off. Started up fine, and made it about 7 miles down the road before it died again (no spluttering, just died instantly). Repeatedly popped the clutch, finally got it going again right before it came to a stop and made it 4 more miles to home. The next morning I changed my inline fuel filter (3/8 clear plastic filter) and my main fuel filter, noticed that my mechanical lift pump had a hole in the housing so I put a delete plate where it was in the block and left the same electric lift pump on it that I had already been using. Bled all of the air out of it, and left it to idle for 20 minutes. Idled fine, full fuel flow to the filter, no air in it. Revved it up while in neutral, held at 3k rpms, all still good. Hop in to go down the road and it does the same thing within a mile, just dies all of a sudden, no spluttering or anything. I limp it back home, and decide to check flow on my electric pump. I get about 1.2 quarts in a minute, this should be about 18gph which is way more than my truck will use. Spray soapy water around injector o-rings while it is running, no bubbles. Checked, double-checked, and re-checked all hoses, clamps, and fittings. Any ideas about what is going on?? I am at my wit's end here... thanks in advance guys!!

 

[vegas39]

Maybe you have a bad connection to the fuel shutoff solenoid. Try running a hot wire from the battery straight to the solenoid terminal and see what happens.
The only other thing I can think of, is maybe the electric pump is picking up air from somewhere. Have you checked the pickup assembly in the tank? Fuel line connections at the tank switching valve? And so on.

The way you describe popping the clutch and getting it going again, sounds more like air getting in somewhere, as opposed to an on/off electrical issue but it doesnt hurt to check both.

 

[cpdenton]

I have to ask. How much fuel is in the tank?

Might have broken shower heads.. When you take off and the fuel sloshes to the rear, you lose suction....

Just a thought.

 

[88fordidi]

I was considering the fuel shutoff solenoid.. could the solenoid also be bad? I know all of the lines from the switching unit forward are good; I'm currently hobbled thanks to tearing the meniscus in my knee so I can't check up under it at the switching unit and can't really lift the bed. And yeah Denton that was my other idea; I'm in the middle of harvest right now and don't have time to lift the bed really.. (it's only been on for 3 years so it should be easier to lift the bed than drop both tanks). I guess I will attempt to fill it completely full with 5 gallon cans and see if that fixes it.. it does maybe have a little bit of air in it at startup; I just can't figure out how it would only leak air going down the road or off? She idles completely smooth and will run at 3k rpms all day in neutral.. air shouldn't be intermittent I wouldn't think

 

[Shadetreemechanic]

At this stage I would grab a two gallon fuel jug, fill it with diesel and plumb your electric pump directly to it. Wire it to the frame and take off. If that solves the problem you know you are looking at the tank selector valve or tank area. If it still dies you are back to looking under the hood without pulling the bed.

 

[vegas39]

At this stage I would grab a two gallon fuel jug, fill it with diesel and plumb your electric pump directly to it. Wire it to the frame and take off. If that solves the problem you know you are looking at the tank selector valve or tank area. If it still dies you are back to looking under the hood without pulling the bed.

Good idea on the fuel can.

Another nice thing about these trucks, is the front tank pickup assembly can be removed without even dropping the tank. The rear tank however is a different story.

 

[88fordidi]

Well, my problem was that my lift pump must have been rated for a rather low amount, as when the problem was just that it didn't have enough flow to keep the engine running after I took off the mechanical pump.. when it died on a test drive I got the key off real quick and found that I had fuel at the lift pump, but the filter housing was dry. Putting on a 14psi electric pump tonight, so that should fix it.

Also, as a note for everyone else; when using a 2 gallon jug, make sure that you hook up your return line to the jug or that 2 gallons will go VERY QUICKLY. Thanks for the help guys

 

[sjwelds]

Actually 14 psi might be a bit much. "they say" you don't want any more than 7-8 psi at the injection pump. Make sure to check the fuel pressure at the schrader valve on the filter base to ensure your pressure isn't too high.

Flow is what you want; not necessarily pressure.

JM2CW

 

[88fordidi]

good point, thanks! I seem to recall that higher pressure on the fuel will have the effect of advancing the timing?
it's hard to get flow without pressure though.. I'm running a facet 7psi pump now and it's not doing the trick. wish I could turn down the pressure on a FASS pump from DPS, I have one sitting on the shelf from our old 24v..

 

[sjwelds]

Fwiw, I am running a facet duralift that's rated at 12-15 psi, and at the Schrader valve it shows 7 psi. So either the pump isn't putting out what its rated for, or there's actually that much pressure drop through the filter head and filter.... Anyway just throwing that out there for you