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1993 Ford E350 7.3 Idi
I have had an issue with the fuel lines pulsating/ thumping for 10 months now. It was rarely at first, and now it happens all the time. When I feel the lines coming of the tank they are thumping/ pulsating. The fuel lift pump is shaking. At one point I didn't have the fuel filter completely tight, and it shook it off and it completely unscrewed while I was driving down the road.
Here is what I have tried with no change:
Replaced the fuel pump.
Dropped the fuel tank- the plastic pickup had gone to pieces, so we replaced that.
Replace the injector pump - because it had low power and blowing white smoke
Replaced the fuel injectors with re-manufactured.
Disconnected the fuel line from the tank to the pump and put it in a jug of diesel- still the same sound. So we know the sound is from the pump up to the fuel filter assembly or injector pump.
We took off the fuel pump and checked the injector cam lobe. It looks correct, though we can't know for sure unless we take it out of the engine.
We can't get a diagram of the fuel pump housing assembly- is there something in that that could be causing this? Check valve?
I had changed the Fuel Filter (Wix) before this sound started- could that cause this issue?
Any ideas?
Remove the lift pump. How does it compare to the old one? Are the lift arms the same length? Inspect for wear. I suspect that the pump was installed incorrectly with the lift arm riding on top of the camshaft lobe. Is there a shiny spot on the bottom of the lift arm? If so, it was installed incorrectly. A properly installed lift pump will have a shiny spot on top of the lift arm. The arm mounts below the camshaft lobe. As the camshaft rotates, the lobe will press the arm down toward the earth.
Edit: Camshaft lobe not crankshaft lobe
Last edited by Perk85F250; Oct 13, 2020 at 09:28 PM.
Reason: Edit: Camshaft lobe not crankshaft lobe
Thank you for your input. Yes, we double checked that it was installed correctly. It made the same sound with the old as the new, and the old one ran for years without having this issue.
As far as I can tell, everything is original. I have seen a couple different routing diagrams for the return lines, but we have just kept it the way it was.
as far as the workings of the lift pump it is common and basic.
while the Outlet fitting is not shown and some cheap Chinese Made Pumps do not have the Pulse Damper in them
This one here is probably more like what you have if you didn't get a quality replacement, of course we don't use the a Return on the Pump so you can Ignore that fitting.
Your first post mentions that it has become worse over time. Inspect the camshaft and camshaft lobe for wear. Not going to be easy to inspect because of where the fuel pump mount is on the engine and the front crossmember. Doesn't leave a lot of space.
Edit: Camshaft lobe not crankshaft lobe
Last edited by Perk85F250; Oct 13, 2020 at 09:29 PM.
Reason: Edit: Camshaft lobe not crankshaft lobe
You mentioned changing the fuel filter before this started... Did the pulsating start right then? If so I'd try swapping the fuel filter again. Not really sure how it could cause a problem like this, but worth a shot if the problem started with the filter change.
Like lonewolf mentioned, there could be parts of the showerhead from the tank stuck in the lines. Disconnect the line at the pump and at the tank, and blow back from the pump end to the tank end with some compressed air. Best would be to catch it all in a bucket (covered with a cloth?) to catch any debris that may come out. Start with low pressure and once the line has "cleared" try to see if the air coming out seems like what you are putting in, or if there might be a restriction still.
The lines have been blown out in reverse with air, so they should be clean. Next step is to take the filter assembly apart and check that as well as changing the filter.
