I have a 2000 F250. After installing a regulated fuel return kit I noticed a knock every now and then when the truck idled for awhile. It began to happen more often and the truck developed a shutter when it hit overdrive and a bit of a sputter under a load. I just replaced the injectors with Swamps AD's, the vibration and sputter are gone but the knock is still there.
It does not do it untill the engine is hot, but once it starts it will do it while I sit at about every traffic light. If I bump the throttle up, it will stop but then slowly come back.
The pickup tube broke in the fuel tank awhile back and it would run out of fuel at 1/4 tank. The sound is very similar to it running out of fuel.
Any ideas would help. Thanks.

 

No comments at all ?!

 

I had a knock in my Ford remanufactured engine almost right out of the crate. It would happen at idle only after the engine warmed up. When you pulled up to a stop, the engine would slow down, hit idle speed then 3-4 seconds later the knock would be there. At first the Ford tech thought it was rod knock as it sounded loudest in the lower parts of the engine. You could hear it very well in the wheel well area.

I used a stethoscope to isolate it to the #7 cylinder. Ford went through a series of tests to include compression check and then finally used a break out box to also isolate it to the #7. Ford replaced the injector and the noise went away.

I hope this helps.

 

If it started after installing the regulated return, I'd start by checking your fuel pressure. Who's set up did you install?

 

maybe air getting in the line.

 

By your description, I'm putting all my money on an air leak into the fuel supply at some point between fuel tank and fuel rails. Which specific regulated return did you install? Have you installed anything in the fuel supply line like a lift pump, post pump filter kit, fuel bowl delete, etc...?

If at any point including the installation of your regulated return, you have worked on the fuel supply there's a chance you have created a condition where you may not have a fuel leak, but air can get into the fuel line.

I've battled air getting into my fuel line at my post pump filter kit I installed after installing a fuel bowl delete kit. At the fuel filter base under the truck I had no dripping fuel on the ground, but a very minor leak that was allowing air into the injectors causing the same kind of knocking you are experiencing. I tried everything to seal the 2 plugs on the filter base and I finally resorted to locating aluminum plugs and fuel fittings and had a local shop weld them to the aluminum fuel filter base. Presto! No more idle knock and the engine is much quieter now at all RPM's.

Like I said, sounds exactly like air getting into your fuel supply.

 

The noise sounds the same before and after the injector swap, so I'm fairly sure I can rule out the injectors. The sound does not seem to be isolated to one cylinder.
The kit I used is Strictly Diesel's. I have tried different pressures 62-68, with no change.
After the install I did have a leak at one of the 45* fitings, snugged it up just a bit more and it fixed the leak. Based on what cutlass wrote, I might try taking the fittings off and reapplying teflon tape.
No other mods to the fuel system yet, Strictly Diesel suggested I do the in-tank mod.
Thanks

 

I also have the ITP regulated return and yes, I would go through all of those fittings and make sure you at least have teflon tape on them to ensure a good seal. I think the ITP instructions mention using Rectorseal #5 and I think that's what I used wherever a thread sealant was required.

 

That does sound familiar and I think I saw some Rectorseal in one of my work trucks. I will not be able to working on it untill this weekend, but I will post results.
Thanks again for the input.

 

Took the fittings out of the front of both heads along with the plug and fitting in the fuel bowl. Cleaned and applied Rectorseal. The knock now only last for a couple of seconds, then goes away. Seems to only happen when I've been running at a constant speed, then come to a stop. If it occurs, it is right about the time the truck comes to a complete stop.
I think I will order the in tank mod. kit and see if that will get rid of the rest of my leak.

 

If I understand the way fuel pressure changes in a fuel supply system correctly, the fuel pressure drops under acceleration and once you let off the throttle, there's a spike or surge in fuel pressure. That's when the demand from the engine is drastically and suddenly decreased while the fuel supply is still at a high flow rate, causing the increase in pressure in the fuel supply line post fuel pump. Your knock for a few seconds may be a remaining fuel leak post pump.

There is probably someone here that knows better than me on this subject. It may be possible an in tank modification may address the issue of knocking a few seconds after truck comes to a complete stop like you said. I think the in tank mod is a must for any 99-03 7.3 powerstroke owner anyway.