Truck is down. Fuel problem. Not sure where to start.

[onetonjohn]

Been having what I thought was fuel drain back. Been fighting this for a while, can't find the air leak. I think it's the return line from the junction on the back of the engine back to the fuel tank switch. There is some moisture (maybe not wet, but not dry either) on and around the switch. Let the truck sit a couple days, and I need to crank crack lines bleed to start.
Fast forward to today. Went though the process, got it running - seemed fine. Drove it a couple miles, parked it while I met with some friends maybe an hour.
Got in it fired right up, ran for a sec, then dies. Not like it had before where it ran for a second. This was running for like 10 second normal, then ramp down to diying - won't stay idling.
Did this a few times.
Fuel pressure at shreader valve.
Floor it, and it will stay running at high RPM. Till you let off pedal then it dies.
I was thinking injection pump.
So I pull the filter and put in ATF thinking this may lube injection pump.
Starts a coupe times with same symptom starts runs, but won't stay idling. Then it wouldn't start. No pressure at shreader valve.
Tow it home.
The no pressure at shreader valve, makes me think the ATF plugged the filter, or the lift pump when out.

No idea why / what the need to mash the pedal to the floor to keep it running was from. Injection pump?

Half of me wants to pull the bed, replace shower head, float, fuel lines, switch, injection pump and lift pump. But I"m just frustrated, cause I can't seem to pinpoint whats giving me trouble. The fuel smells old to me - like lacquer thinner, but my friend said it was find. It might be a year old. Any help is appreciated, as I'm at my wit's end on this one. It was good while it was running good, but now it seams like it's all problems I'm having trouble fixing despite spending a lot of time trying to fix it.

 

[IDIBOBS]

you just have to slow down and think about things. Take the filter off. Crank it over. Do you have fuel? Yes? Problem is after lift pump. No? Problem is lift pump or before. Is the tank full? Duel tanks? Does it happen with both tanks? If you have had a return line leak why haven’t you replaced the return line. It’s cheap and easy. It bet off the top of my head your port pump is bad.

 

[onetonjohn]

Port pump is the mechanical lift pump? That's what I was thinking cause no pressure at the shreader valve at the end - I did have pressure in the begining, which is very strange that it would go out while I'm trying to get it started. I have two fuel tanks. Fuel tanks are not full, but do register a bit on the fuel gauge. 1 is low - less than a quarter, the other a little less than half. I did try starting with both of them.

Didn't replace the line cause it doesn't look like you can get them any more. Or at least I can't find the one I want (return line mixed nylon/rubber from back of tee to fuel switch. Thanks for reminding me to slow down. I'm frustrated because I don't know how to map the symptoms I'm seeing to definite problem - like I have to mash the pedal or it stalls. I've never run into this before. That said, I don't need the truck for work, and I have time to sort it out. I'm a little embarrassed that I haven't been able to fix it yet. I've read a lot about these types of issues, and thought I had a handle on the drainback issue, but this seems like something different. But it's just showing what I don't know. I suppose you can't learn unless you try. So here I am. Learning. Ugg.

 

[onetonjohn]

The brown truck was always the one that ran good that I could use while I worked on project little foot (same truck, but white, and a 5 speed instead of automatic). Now I' have two broken trucks. Actually the white one starts and runs. Needs lights, tailllights and to work the bugs out before it's road worthy. But yeah two broken turcks.

 

[onetonjohn]

Can't sleep. I got a theory while I was laying awake stressin'.
Debris in the tank (showerhead bits?) was getting sucked in an clogging the line, and that's why it would run longer than fuel drainback, but wouldn't idle.
Full throttle got the lift pump moving fast enough that it was pulling fuel in anyway, but if you let off, not enough would get in (lower RPM lift pump action).
Went dry after I switching tanks and then I started getting no start at all cause fuel level is below broken showerhead (gauge was not empty). From there on it was no start, no pressure at shreader cause out of fuel. The stars would have to align just right - so I may be making this up, but more and more, I want to pull the senders off the tanks.

Question. This seem plausible? If I am on the right track, would you drop tanks, or pull the bed? I remember dropping the tanks on the other truck was kinda a pain. In ferry-tail land, all I gotta do to pull the bed is unhook taillight wiring, pull the fuel hoses off the tank, and 6 bolts. I need some superduty bolt replacements handy for re-assembly, cause I distroyed about half the bolts getting them out last time.

 

[frankenwrench]

I personally hate either option, but end up dropping tanks rather than lifting bed. Your theory seems quite plausible and I'd personally go for it. And while your at it blow the lines out with an air compressor from the filter housing back to the switch valve. Also from return t back to switch valve. After disconnecting from switch valve of course. And disconect lines between switch valves and tanks as well and blow them out as well. May as well dump tanks and clean everything out while your in there. Pull bed, or drop tank, up to you. But a good cleaning and new shower heads and appropriate level of diesel in tanks never hurts. Also, just behind lift pump is a service loop that tends to deteriorate over time and develops leaks as well as collapses internally. If it even insinuated that it was a bit old, just replace it. Best of luck bud!

 

[onetonjohn]

"Also, just behind lift pump is a service loop that tends to deteriorate over time and develops leaks as well as collapses internally. If it even insinuated that it was a bit old, just replace it".

What's the service loop? Is it a section of rubber hose in the steel line? A junction with a port? Something else? Is it between water separator and the lift pump? Don't remember seeing anything like this.

 

[KansasIDI]

"Also, just behind lift pump is a service loop that tends to deteriorate over time and develops leaks as well as collapses internally. If it even insinuated that it was a bit old, just replace it".

What's the service loop? Is it a section of rubber hose in the steel line? A junction with a port? Something else? Is it between water separator and the lift pump? Don't remember seeing anything like this.

It’s a little piece of rubber hose that is attached to the steel line from the water separator and lift pump.

 

[Old Goat]

I would rather remove the Bed, done it 4 times so far.
I thought the bed Bolts were just carriage Bolts. The nuts on the Frame were so rusted they wouldn`t move. With fuel lines close on the L/F didn`t want to attempt that.
Figured I could grind off the heads and they would drop out....way they are made, only dropped down a couple inches.
Lifted bed, and torched them off between bed and top of Frame.
Replaced Bolts with Hex Head, large washer on top an a Washer and ny-lock on the bottom with Anti-Siez.
I bought one of these Bed lifts, here is on on e-bay, price has really come down since I bought mine.
I use my Cherry Picker, move truck then set bed on saw Horses.

Pardon Our Interruption...

Or Google lifting truck bed etc... ton of info.

It Could be your Lift Pump going out, I noticed mine wet on the bottom but not dripping. As mentioned above the Curly Q Hose connecting Pump to steel line could be cracked. Mine was cracked pretty bad at the 2 clamps.

Problem could be you are just too low of fuel in the tanks, as old as the truck is, the Shower heads are in the bottom of the tank. 1/4 tank or so you are sucking air.
Where the steel line from the IP and the 2 Injector return lines connect at the back. I think there is an Olive on that steel pipe.
It if original is hard and cracked and should be replaced.


Goat

 

[IDIBRONCO]

I'd look at the lift pump. It may be able to supply just enough fuel to start the engine, but not let it run even at an idle. The injector pump will draw enough fuel to run the engine, but not at an idle. That could explain why you have to use high RPM to keep the engine running. Running the engine without enough fuel flow from the lift can be bad. The fuel flow keeps the IP cool. Without it, you can and probably will wear out your IP internals. I had that happen to me. You probably haven't run your engine nearly enough to do IP damage since you haven't been driving it. Your IP should be fine.

 

[onetonjohn]

service loop and olives are new. Once I get some time, I'll put vaccum at the service loop and see if I'm pulling fuel from tank. Supposed to rain this weekend. Maybe pull the bed next weekend and do shower heads and floats and blow out lines. I bought extras when I did the white truck thinking Id need to do the brown truck at some point. I guess that time is now. I'll keep you posted what I find.

 

[onetonjohn]

Gonna try the bed lifter for 150 bucks. Last time I built a frame out of wood and it was a little sketchy.

 

[Larry P]

Before you drop the tanks or lift the bed. Do this: splice a clear 3/8 line between the lift pump and the filter head. Look for bubbles and move upstream or downstream from there if you see them. If upstream, splice a clear line to the lift pump inlet. If you see air there, remove the air water separator and replace with clear line (or splice in clear line where the separator was, if already removed). From there, go to the fuel selector valve outlet, then each inlet as necessary. Only THEN drop tank/s.

 

[onetonjohn]

Some of those will be tricky, as they are metal or nylon point to point lines, but I understand the idea. Find out the issue BEFORE taking it apart. Point taken. I will do some more checks before taking it apart.

 

[onetonjohn]

Got some time to work on it today. Of course, I had fuel to the fuel pump and it fired up after bleeding a bit. I went with debris clogging fuel line theory and pulled off the bed. Shower heads missing, but bits in the tank. Floats were OK, but senders are shot - Reading mega ohm values for all but empty. I think they read different submerged, but that's probably not a good sign. Fuel gauge is wonky, so gonna replace senders. I think I can get them at gas tank depot or bronco graveyard. I need to get the Diesel for 80 - 86 model which is harder to find. Put some primer on the frame while it was in front of me and cleaned 30 years of dirt and grime out of frame rails. Found a set of keys wired to the frame. Pretty cool trick, but now that things are cleaned up they are easier to see.