I have an '88 F450 with a 7.3 and have the following problem:

The fuel filter light started to come on one day a couple of weeks ago, accompanied by the engine coughing from, I assume, fuel starvation. So, I replaced the fuel filter, but there was no improvement, the light would still come on under light to moderate load and the engine would cough and/or stall. In order to restart the truck I would have to bleed a good amount of air from the fuel filter via the bleed valve on top of the fuel filter housing while turning the engine over to operate the mechanical fuel pump. Once started, the truck would idle with no difficulty, but once under load for a couple of minutes it would begin to cough as the fuel filter light would come on. This truck is equipped with a combination fuel filter/water separator. There is no isolated water separator on this unit.

Thinking that there may be an air leak on the vacuum side (upstream) of the fuel pump, I installed a new 10' X 3/8" line bypassing everything between the fuel pump and the 2' long X 3/8" line coming out of the fuel tank. This line coming out of the fuel tank maintained a steady siphon for two minutes when I disconnected it from the original fuel line, so I have assumed that there is no obstruction there. Still no improvement, engine still coughs and stalls under sustained load.

Then I replaced the mechanical fuel pump, thinking that there may be a lack of output from the old one. Sure enough, the new pump puts out more pressure and seemingly reduced the problem to some degree (now I can maintain about 30 MPH or so, anything above that causes the fuel filter light to come on and the engine to cough/stall). Problem still not solved.

Thinking that the return line from the injector pump might be obstructed (a friend said that an obstructed return line would cause it to run rough or not run at all), I disconnected the return line at the injector pump and blew through it with little resistance. I could "feel" the fuel clearing the line and could then hear my breath bubbling into the tank. I also remove the check valve where the return line leaves the injector pump and found it to be clean and freely functioning.

To recap, I have replace the fuel pump, the fuel filter, the fuel line from pump to the short line extending from the tank, as well as finding that the return line is clear.

Quite frankly, I'm stumpped. Any pointers would be greatly appreciated.

Thank you,
Bryan Barnard

 

Since you ruled out all the possible problems fuel line ,lift pump and fuel filter the logical solution is to replace the injection pump,the injection pumps on those engines are usually good for about 75000 mi. and not knowing whether you're the original owner or have recently replaced the pump or have records of the last pump replacement I feel confident that thats where your problem is,as far as the fuel filter light you mentioned,this is just a warning light that tells you when there is water in the separator bowl and has no connection to your problem unless you have some bad fuel with very high amounts of water in it,its sounds as if you repaired the problem of having air in the system by replacing the lift pump or fuel supply pump
which are notorious for causing this problem.Save your self some time and a lot of grief and replace the injection pump Its not that hard to do and if you haven't done it before I'll gladly give you step by step instructions

 

This Truck is equiped with both a water in fuel light and a restrition indicator light. Now to the problem ? I had the same problem but had an auxillay fuel filter that was getting pluged that I installed also replaced the Ford factory filter. My problem went away. I have had to replace the filter housing because it was sucking air and would let the fuel bleed back to tank and it was not the check valve that caused this. I would be looking at replacing the housing and Maybe another new filter. As for injection pumps they do wear out, I had one that would let me start my truck cold no problem but as it warmed up I could not start it the pump could not creat enough injection presure to fire the injectors. For my money I would try another new filter first. Than a filter housing if the filter did nothing.


HAAKEYE snow fever for sledding but does like his trucks. Want to get the F100 ( Ground Pownder) back on the road soon.

Yahoo messanger (haakeye50)

 

Mystery Solved!

I went ahead and installed a fuel pressure/vacuum gauge and found the idle pressure to be at 5.5#'s, but when I'd take it up to 2500 RPM and sustain it there under load, the needle would drop, and, passing zero, go to pulling 10" of mercury. So I decided to assume the newly replaced pump was defective from the factory and went ahead and replaced it. This one works fine, idling @ 5.5 #'s and putting out no less than 4#'s at 3400 RPM.

The moral of the story: While it is usually unlikely that a part is faulty from the factory, don't assume perfection from a part simply 'cause it's new, like I had originally been inclined to think.

Many thanks to those who replied.

Best regards,
Bryan Barnard

 

Your wellcome @ it's nice too know not everything is perfect TOUGN in cheek

HAAKEYE snow fever for sledding but does like his trucks. Ran a 13.049 at 103 mph in my 1970 F100 ( Ground Pownder) 428scj 2/4 4speed. Yahoo messanger (haakeye50)