I have an early 99 f 350. And after a good heat soak I lose all the fuel pressure. All this started after doing the intank fuel mod. I have removed the tank 3 times and know that is not the problem. Then i replaced the fuel pump and still have the same problem. I have a fuel pressure gage installed on the right head and at start up I have 60 psi and the warmer the engine gets the more it starts to fluctuate untill there is no pressure at all. So the other day I was stuck in a grocery store parking lot and I pulled the return line off and it was dry so I know that is not the problem. Then I checked voltage at the pump and it was 13.8 VDC. I am trying to check all the grounds but I cant tell were the the one for the fuel pump is. I have had it on a scanner and can not find any thing out of the ordinary. Oil pres is good no cps code map is good injector buzz test was good. I did get a icp high low code and have a new icp but have not put it in yet because it is reading with in spec on the scanner. I am at my last straw here and will soon be throwing some high dollar parts at this thing.

Any and all help would be much appreciated I am new here and hope you can give me some insight. Thanks

 

The ground for the fuel pump goes to a GIANT splice (s102 in the engine harness near brake pressure switch) that pretty much grounds everything else at G100 (Driver's rear cowl by junction box), including the PCM, lights, wipers, instrument panel cluster, etc.

 

thanks I have pulled on that one sounds like I will have to dive into the harness to find the splice. What are the odds I have a bad new pump?
The air dog II is soundin real good.

 

Slim to none. Look elsewhere. Your problem started with the in tank modding so that is where you need to look. Something happened from that operation. Since you have had the tank down three times, I would make provision to see the fuel flow after the pump and then right after the filter bowl. I am talking a provision that allows you to check after a "heat soak" or whenever it exhibits the symptoms. From there go forward or backward in the fuel path.

None of this is computer controlled except for the on or off mode. Good luck.

 

I have a clear filter before the pump. there was air in the fuel but i fixed that the last time I pulled the tank. I have checked the lines with a mighty vac. they hold the max of 25 pounds of vac. what can I use to see the fuel after the pump when it is at 60 psi?

 

Is the clear fuel filter rated for suction or for pressure. If it is before the pump it needs to be rated for suction, Maybe it is closing off under the suction. Sounds like it could be your problem.

 

its not much more than a sceen in a glass with removable ends so it can be cleaned. it seals up very tight and looks alot like the sceens I took out of the tank. I think it is an empi part. It is strange to have enough fuel to go 10 miles and then just barley enough to idle roughly. where is my fuel pressure going. sorry for the frustration thanks for the help.

 

Could one fo the hoses be pinched off between the tank and the body of the truck. Or a hose being sucked flat. What kind of hose did you use, is it rated for diesel. Just things to think about.

 

I used regular 3/8 fuel line. All I know is it is not rated for fuel injection. Can you suggest a hose that will not colapse under vacuum.
Thanks for the help. When I took the tank out the other day I made sure the hose was not pinched. Can any one tell me where the fuel pump relay is? Some one said it was part of the fuse block but I cant hear or feel any of the relays clicking when the pump turns on and off. the only noise I hear is coming from the middle of the dash some where.

 

re-route the discharge to flow into a bucket and measure the flowrate

 

3/8 30R9 Fuel Injection hose is stiff enough that it will hold up under vacuum. I would think that if your standard 3/8 fuel line is collapsing under normal conditions that you would have to still have a severe restriction in or close to the tank.

When you did the in-tank mod, the pickup foot can not be sitting on the bottom of the tank, it needs a small amount of clearance. Measure from the top of the inside of the lid to the bottom of the pickup foot. Then measure the tank from the top of the opening for the lid to the bottom of the tank. The pickup assembly should be 1/4 to 3/8" shorter than the depth of the tank.

Did you eliminate the in tank mixer screens?

 

This sounds very close to what Pat (justanothertruck) ran into when he did his intank mods. IIRC he ended up with one of the lines being a bit to long and it would pinch closed from time to time. I am sure that he will chime in with some input here for you.

 

I was thinking collapsed fuel line too. Happened to me in a different truck where it passed under the cab. Just by chance I found it after pulling the bed and checking and changing many parts. Good luck and don’t get too frustrated, you'll find it.

 

Oh yeah.. sorry it took so long for me to chime in.. i stay away from this subject.. it brings back BAAAAAD memories.. I would go with a pinching line, the other thing it could be is the depth of your pick up. Did you measure before you removed teh mixer?
See, I had not, what I measured was to the bottom of the tank, well, the tank was sitting on the ground, pushing the bottom of the tank up..

 

yes I measered the pick up tube length and the tank depth. It was 15 inches on both with the tank on the ground. I figured it would gain a little when slung under the truck. I think the last time I had it out I adjusted it to 14 3/4 but I will check it when I have time this weekend. The lines run in the stock location tucked in to the frame rail. The hose I used says it is (not rated for fuel injection) right on the hose. I figured it would be ok on the suction side of the pump. I will get some clear hose and run it from the regulater in to a bucket this saturday but I pulled the line off when it was acting up and had nothing. I am going to try and bypass the relay and see what that does. I have messed with the fuel lines enough that I cant see that still being the issue but Im not going to over look your advice. I will check it all again. thanks