Just bought a '93 F-250 w/7.3 non turbo diesel.

To make a long story short, I started it the afternoon to pull it into the shop. It started and ran normally, but after about 30 seconds, it rather abruptly quit and wouldn't restart.

There is air at the schreader valve on the fuel filter. Tried a few things, but couldn't get it running. I notice in the manual that Ford is pretty adamant about not letting it run out of fuel and that doesn't give me a good feeling.

What is the procedure to purge the air? On one of our tractors, there is a little hand pump lever on the engine driven fuel pump to do this, but I don't see one on this engine.

Thanks
Craig

 

its a very common problem on these to have air leak into the fuel lines and siphon the filter dry, but that usually results in it starting and running for 3-5 seconds before stalling out like yours did. you can find tons of threads on the subject if you search "air intrusion"

to get it going again, you can either add an electric pump to prime the system, or sit there and crank on it for awhile. the starter should be run for no more than 30 seconds with a 5 minute rest (coffee break). when i was fighting this on my IDI, it would always come to life at the end of the second 30-second round of cranking, at which point the batteries were getting pretty low. this is the standard method for dealing with it.
but many of us don't like abusing our batteries and starters that way, so we add an electric fuel pump to the system. note that you should never have an electric pump pushing through the mechanical pump unless the e-pump only runs on a momentary basis, otherwise a lift pump failure can allow fuel to be pumped into the crankcase quickly. so either have an e-pump instead of the mechanical, or have it on a momentary switch and just use it to prime the system.

 

I looked around at some other threads. Gave me some more insights, and more questions.

Josh, you make it sound like I can put an electric pump in series with and before the normal mechanical one. Is that right? In that case, the mechanical one pulls through the electric one when it's turned off?

If the electric pump fills up the filter, is that all that's required? Is it necessary to bleed the lines from the filter to injector pump, or from injector pump to the individual injectors?

How in the world did they do it the first time...when it had just rolled off the assembly line?

Once the engine is running, how does it handle momentary air bubbles that may come from the tank. Like with low tank and hard turn momentarily sloshing the fuel away from the pickup? Does the filter have provisions to handle this?

Another thread described a check valve in the return line from the filter. If I understand this setup...the engine driven pump moves more fuel than the injector pump takes in. The excess is piped back to the tank through a check valve near the top of the filter. The injectors also have a return flow that joins the filter's return flow, but downstream of the check valve. This way if an injector return cap leaks, the check valve isolates this leak path from the supply of fuel in the filter, and the filter does not get an air bubble in it. Is this right?

I'm going to have to replace the rear tank...it's seeping. The return line is kinked next to the quick connect at the tank. The local auto parts store can find Dorman fuel lines and quick connects for gas trucks, but not listed for diesels. Are they interchangeable? I know that diesel is hard on some rubbers/plastics. Are there other sources for either complete lines, or just the quick connect with a barb on the end to use to connect regular fuel line to the tank?

Thanks
Craig

 

on my rig, i have a carter pump installed inline with the mechanical pump, with the e-pump pushing through the lift pump, or the lift pump sucking through the e-pump. its wired so that the pump runs on exactly two occasions: 1) when the glow plugs are lit, and 2) when i hold a pushbutton.
with this system as i built it, i turn the key on to wait for the plugs to warm up, the e-pump kicks in and primes the system, and when i reach for the starter, i never have to crank for more than 2 seconds to have it purring like a kitten

when air intrusion occors, it siphons the filter dry, along with all the injector return lines, but doesn't affect the injector lines at all. the fact that it starts for a couple seconds then stalls seems to be proof of that.

i would suspect that at the factory they used some kind of connector that engaged the schrader valve on top of the filter housing, and either pumped fuel in from there, or pulled a vacuum there to suck fuel up from the tank, i'm not sure exactly. but when i had my rig all torn apart a couple months ago, my e-pump was working, and it only took a few 30-second rounds of cranking before everything was purged of air and running as it should.

if you look around your engine, you notice a small return line from the filter head and a large one from the front of the IP. the one on the filter head is primarily to deal with any air bubbles in the line, and send them on down the return lines. but anything that gets past that will end up at the top of the IP, where it quickly finds that return line.

as for putting a check valve in the filter return line, i haven't heard that exact version, but i have heard that ford suggested plugging the ports for that return line, as doing so prevents many air intrusion issues. i've also heard of adding a check valve in the return line after the tee at the rear of the engine. all of these versions serve the same purpose, to prevent fuel from siphoning back to the tank when air is introduced upstream, and i suspect they all work equally well.

all that said, there are 2 categories of responses to air intrusion: prevention, and cover-up. solving leaks and playing with check valves prevents most cases of air intrusion, while adding an electric pump covers up all symptoms of air intrusion by priming the system first.

as for the lines at your tank, i haven't checked for OEM-style lines, but if it was mine, i would hit your local auto parts store and buy a section of hose rated for diesel fuel in the correct size, cut off the damaged fitting from the plastic line, and slip the hose over the plastic line for a few inches, using a couple of hose clamps on it, being careful not to clamp them down hard enough to crush the plastic line. this is what i did for all connections when i replaced my tank selector valve with a universal one, and it works fine.

 

Thank you for the help. Excellent answers. That all makes sense and covers things from both practical fixes to why it happens in the first place. I really hate working on stuff when I don't understand what's going on in the first place.

Thanks
Craig