SD22 Runs - then doesn't

[Xonk61]

My truck has been gradually declining, it will run for miles, then, especially when going up a hill, when I shift into a lower gear and increasing RPMs, start chugging. I replaced the fuel filter, bled the air from the lines, and thought I had it done. Then the test run, (about 3 miles) left the truck stranded at the side of the road. First thought was that I'd not completely bled the air from the fuel lines, but it seems it wouldn't have gone the 3 miles if there was air in the lines. I'm borrowing a neighbor's car to pick up an air filter this morning, (it's due for one of those too, but I had to order it, not a stock item... like the fuel filter also wasn't!) Any ideas of where to look next for why the truck will run, then choke up and quit? It really acts like it's not getting fuel.

I got the truck towed back to the yard, removed the old air filter, and found what may be another clue. Something I've not seen before, the inside (engine side) of the filter appears loaded with soot. I don't know what that might be a symptom of!

OK, air filter is installed, fuel line from filter to pump is removed at the filter, the line from the pump to the filter is still in place. Manual pumping of the primer occasionally squirts fuel from port on filter assembly, almost as though I hadn't filled the filter with fuel prior to installation.

Where will a bled system begin to pull air back into the fuel line?

[plenzen]

Sounds like you have a number of things going on here. The soot inside the air cleaner is most likely blowby. Engine may be getting a bit tired.

Temporarily run clear plastic lines from your tank pickup all the way to the fuel filter inlet and then from the fuel filter output side all the way to the lift pump. You are getting air in the system from someplace and its simply running out of fuel. Another thing to check is if the vent in the fuel filler cap is plugged and your simply sucking all the air out of the fuel tank. Easy way to test this is to drive it with no or a very loose filler cap and see if the problem goes away.
The clear lines will give you a good indication as to whats going on and where the air is entering the system.
There is no need to bleed the fuel lines to the injectors as this is a self bleeding system.

Good luck

[Xonk61]

I've disconnected fuel lines from lift pump, and installed a clear hose from the fuel line coming from the tank to the intake of the lift pump. Manually pumping the lift pump brings fuel into the clear line, but doesn't bring it all the way to the pump. When I stop pumping, the fuel in the clear line recedes back toward the fuel tank. I would think that there's a valve inside this lift pump to keep the fuel from receding back. Trying to remove just the lift pump, 2 of the nuts holding it are accessible, the third, (lower, and toward the front of the vehicle) is in such a tight spot that I can get an open end wrench onto it, but there's no room to work the wrench. Is the lift pump installed before the injector pump is mounted to the engine? I was hoping I could remove just the lift pump, and open it, find out if that's where the problem lies...

[plenzen]

Have you opened the bleeder screws on either end of the fuel pump and purged the air ?

[Xonk61]

I did attempt to purge the air from the injector pump, but at this point I'm trying to get the lift pump to even pump. All the other lines are removed from the system, other than the one line going from the fuel tank to the lift pump. the line from the lift pump to the fuel filter is not in place at the moment.

[plenzen]

Did you try opening the bleeders and pumping at the same time they are open ?

Edit:
Just re read.
Maybe disconnect the output line to the filter and see if you can pump into a jar or can. Then move forward from there.

[Xonk61]

it's essentially what I've done, such that only the lift pump it connected to any lines, and it seems like there should be a valve in the lift pump that prevents the back flow of fuel.
Now I'm in the process of trying to remove the lift pump without removing the entire injection pump. Two of the nuts can be accessed, but the last one, below and toward the front of the vehicle is in such a tight spot that a wrench cannot reach it, nor can a socket. I'm not sure if that last nut can be removed without removing the entire injection pump, so I'll take some time making notes and taking pictures to be assured that when I reassemble the whole thing, I'll know how it goes back together.

I certainly appreciate all your suggestions and help you've provided. I'll continue updating as I learn more.

[plenzen]

If you use the search function on here and enter "lift pump" there are many entries from people that have had a myriad of issues with lift pumps and different solutions to solve them. 90% have been clamps, hoses, plugged filters etc. Perhaps go there and read through a few. I guess I just don't want to believe that one of those pumps is dead.
That being said.......I have been wrong before... seen it happen.

[Xonk61]

Back to it again today, after borrowing a neighbor's truck to get to the auto parts store, and coming home with an electric fuel pump, I decided it was worth a try to convert it.
In the process of tidying up under the hood and reassembling what needed to be, I put the banjo fittings in place on the lift pump, and found the filtering screen. In the bolt that holds the banjo fitting onto the lift pump. I have looked through the service manual on this truck/engine, and the posts online, and didn't realise the screen is threaded into that bolt!. I unthreaded it, cleaned and scrubbed and dissolved the tarry residue that filled the gaps, reinstalled, and was pleased to see that the lift pump is pulling a good vacuum again!
So the truck is running, better than it has for a while! Much thanks for your help!

(still going to hold onto that electric pump, just in case I've overlooked something else!)

[waynosworld]

That is great that it's fixed now, I was unaware of the screen you are talking about, did you take a photo of it?
Is this screen connected to the actual bolt that holds the banjo fitting on the bottom of the lift pump?

Back to it again today, after borrowing a neighbor's truck to get to the auto parts store, and coming home with an electric fuel pump, I decided it was worth a try to convert it.
In the process of tidying up under the hood and reassembling what needed to be, I put the banjo fittings in place on the lift pump, and found the filtering screen. In the bolt that holds the banjo fitting onto the lift pump. I have looked through the service manual on this truck/engine, and the posts online, and didn't realise the screen is threaded into that bolt!. I unthreaded it, cleaned and scrubbed and dissolved the tarry residue that filled the gaps, reinstalled, and was pleased to see that the lift pump is pulling a good vacuum again!
So the truck is running, better than it has for a while! Much thanks for your help!

(still going to hold onto that electric pump, just in case I've overlooked something else!)

[Xonk61]

I wish I had taken a photo of it. When the bolt is removed, at the threaded end of it, (the part that's inserted first) a plastic tip will be seen. I noticed 4 slots on it, as though it was a screw, and thought that I might try to gently try removing it. it took 2-3 turns to unthread it, and then it slid out of the bolt. This revealed a cylindrical grid that extends through the length of the banjo bolt.

I will be breaking the seal on the fuel lines again soon, (the fuel lines need to be replaced) and when I do that, I'll go ahead and remove the banjo bolt too, and take photos of the screen.

[plenzen]

Glad you found it and the repair was ,,,,,,,,,,,,,,,,,,,,,,, "cheap".