My truck has been sitting since Friday, while I was working on the driveline. When I tried to start it this evening, I ended up draining my batteries.

It never occurred to me to see if there was air in the fuel lines, until I went out for round two. I had the batteries on charge for about an hour and wanted to see if it might start. I also had the block heater plugged in. I knew it wouldn't take too much on the block heater since the garage has been heated all day today.

After trying it one more time, I decided to see if there could be any air in the fuel system. There was all kinds of air!! Once I bled it off, the truck fired on the second crank!

So... I have an electric lift pump and new return lines.. I'm wondering if this has been my problem all along. Every once in a while, it would be kinda hard to start. I figured it was my WMO fuel mixture. Tonight, however, it was on my straight #2 tank.

With an electric lift pump, I should be able to see any fuel leaks... I found none.

My questions are:
1) where else could the air be coming from? (I triple checked my 2nd filter mod.)

2) How much pressure should the air or fuel have at the scrhader valve? (Could my return lines be blocked?)

3) Where could I find a decent check-valve that will fit the 3/8" fuel line I'm using? (I know the lift pump has one, this might be good for diagnostic purposes.)

 

If you have much over 7 PSI, the timing is going to get weird.

Higher pressures advance the timing.

 

Do the clear hose test on this page...... may have to do some reading for air leaks into.

Ford diesel 6.9 7.3 IDI

 

also, air leaks in the fuel return system do not automaticaly mean fuel leaks.

you can have an air leak, but no fuel leak.

 

Air molecules are much smaller that fuel molecules.

By the time you see fuel leaking out, you have some bad leaks.

 

I understand that, but why wouldn't my electric lift pump be able to push the air on through the return lines? When I bleed the air from the schrader valve, it comes out under pressure. I know these lift pumps don't produce much pressure, but should it be like that? I would think that the return lines would keep the pressure low.

The way I understand how this fuel system works, is that the lift pump pushes the fuel through the filter(s) and gets enough volume to the IP. The IP should pull what it needs and allow the excess to go into the return lines. Any excess pressure in the fuel system should be taken care of by the return lines.

Are there any places that the return lines are known to get clogged? I know it's difficult to reach, but should I try the plastic line at the back of the intake? I can turn down the output pressure on my air hose, to be sure I don't burst the line.

 

What electric pump do you have on it? When I put my holley pump on mine, it worked good for about a month. It would pump fuel great for about five minutes, then just about quit pumping with no change in pump noise. It may be sucking air from the pickup tube in the tank. If it is sucking air between the pump and the tank, you will have no way of knowing. run it out of a five gallon bucket or something. Get volume and pressure checks normally running, and running it out of a bucket.


What I ended up doing with mine is, I put a 105 gallon tank on the back, took off and threw the electric pump in the garage, ran new fuel line all the way to the new mechanical fuel pump, bypassed the water separator, put a fuel pressure gauge on my schrader valve, put clear fuel line or my return lines under the hood, and put on a new fuel filter. Problem solved.

 

You'll probably have to go to Grainger for the check valve - I've searched everything from home centers to NAPA to plumbing supply places for a suitable check valve to no avail. Don't know about the pressure but the air is likely getting in when the electric pump's check valve doesn't hold and a small air leak breaks the vacuum that holds the fuel up in the system. I had precisely this problem with my truck this morning at 5 - I put the mechanical lift pump back in the loop and disconnected power to the electric and my problem went away.

These engines are very unforgiving in the air in fuel department. I had a thread going about this a few months ago: I've worked on lots of diesels but in my experience the 7.3 is much harder to restart after air gets in and to keep air out in the first place.

 

I have a facet dura-lift pump on mine. The only problem I had with it, was not having it on a relay. When I originally installed it, it was an emergency job. The mechanical pump started spewing fuel everywhere. I took the pump off my 87 and just threw it in real quickly, without putting it on a relay. It wasn't getting enough juice and was very noticeable. It now has the relay on it and pumps great.

It would have to be outside the tank, since it was doing it on a full tank. I will be trying the bucket test, as soon as I can.

I just got a 105 gallon tank in the bed of my truck... Sounds like an idea!

 

If the electric pump runs long enough, it should push the air back through the return lines.

Where is the electric pump located in you fuel lines?

 

It's mounted just forward of the FSV.

 

if it has a pinhole in the steel line right where it meets the tank, or the push-on fuel line connector is not sealing completely, it wouldn't make any difference if it was full. With the 105 gallon tank in the bed, there is zero fuel drainback issue. no need for a check valve anywhere. I've tried putting a facet pump on mine too, but it just doesn't seem to keep up with the demand. the mechanical pump works exactly like it should. FYI, I cut a flap in the plastic fenderwell so when I put the new mech pump on it, I have a clear line of sight to the camshaft lobe, and the bolts. Much easier to install when looking directly at it, instead of at a weird angle with no light and the arms bent all stupid and stuff. i was about to pull my hair out trying to figure out what was wrong with my truck. Have you checked your fuel pressure and volume yet?

 

Actually if you pull the vacuum pump off first, you can do most of the swap from the top.

 

lol, but dave, I don't want to pull the vacuum pump off. Every time I start fixing something that is broken, I find more stuff I need to fix. like the rear brakes, buy new wheel seals, replace all of the hardware, springs, shoes. Haven't replaced the parking brake cable yet though.

 

Two 10 mm bolts drops the vacuum pump bracket off the alternator bracket.
Lay it aside, then you can see both lift pump bolts.

Loosen the steel line that goes to the fuel filter first.
Then 1/2" shallow socket, 3" extension and a rachet and you are good to go.

Much better than laying under the engine reaching up with stuff falling in your face.