Daviedoall

I lost prime on my 1992 Cummins installed in my camper due to a clogged fuel pickup screen in the tank. It is running again but there is flurry of bubbles showing in the visible fuel return line I installed. Is this ordinary? it is a flood of bubbles not the odd one. It continues after I shut the engine down. Seems strange, please help!

My handmade camper in her 40's now

oliver foster

Cool rig.

The air bubbles should not be there. You have an air leak in the lines somewhere between the IP and the fuel tank.
Check all fuel line connections, at the fuel tank, LP, fuel filter, ETC.
The fuel lines themselves can also crack and allow air in the suction side of the fuel line on the way to the motor.

Daviedoall

Thanks for the input and ideas. I have made a small replacement fuel system with a 5 gallon plastic gas can with 3 gallons of diesel in it. I have an electric pump feeding through a plastic fuel filter then directly into the injection pump. The return line and the supply line are see through vinyl and the return line goes into the gas can.
When I energize the electric pump, fuel starts to circulate through the system and bubbles are pushed out until no more come out after a minute.
Turning the engine over causes bubbles to come out the return line. I bled the injectors twice and got it started. It idled and would rev up some, But when I put it into gear there was no power and the truck could barely move under it's own power. It was rough sounding trying to get it to rev and it died suddenly with no restart.
What could be going on? Where are all the bubbles from? There are still lots when it is idling. Help !!

Daviedoall

I am desperate so I moved a copy of this post to the Help! section where hopefully more folks will see it and comment with ideas. The Camper is broken down away from home and needs to come home.
Thanks, I hope that's OK here
David

nonrev

IIRC some one recently was talking about a similar problem it turned out to be a bad injector, it was not closing and the compression was entering back into the injection pump

Daviedoall

Thanks for the idea. I have a set of injectors on order. I'll let you know it they fix it Yesterday I loosened all the injector lines like to bleed it and gave it a serious spin. No Bubbles in the return until I tightened the injector lines again. Then they came back. I'd like to think this shows a bad injector not sealing against compression pressure coming back through the injector into the pump.

Daviedoall

I installed new injectors and the bubbles have disappeared! That's the good news. The bad news is it won't start. It will hit on what sounds like 3 cylinders and then stop.
It will do this over and over and over, act like it's starting and then die. I'm out of ideas so if someone has an idea I'd like to hear it
What is the piece under the injection pump? Should it be energized too for starting?
Thanks,
David

nonrev

If this is what you are referring to it is the KSB and it advances the timing on cold starts, so for now that wouldn't be the problem. Did you have the throttle shaft of by chance? if you did you might not have indexed it correctly

Daviedoall

Thanks for writing. I never had the throttle shaft apart. I did take a look under the cover under the smoke screw. I had wondered if the diaphram was holed. Could the fuel pin have dropped into the bore? It felt like the plunger went fully down when pressed. Maybe I should look again?

nonrev

The slide pin wont come out that way. you can chech the slide pin to see if it is working and not froze up .. pull the fuel pin and look into the bore then open the throttle by hand, it should pop out then just slide it back in with a pick or small screwdriver.
You say that you have an electric fuel pump on it, how many psi is it making, these ve pumps will lose the front seal over 16 lbs and dump the fuel into your pan. Are you getting good psi at the injectors? It should spray pretty hard when you are bleeding them

edwinsmith

The obvious question is did you do a thorough job of priming the injectors? You have to get all of the air out of the fuel filter, then the VE pump by loosening the return line banjo while pumping the manual lever on the lift pump. Then you need to crack all of the injector lines at the injectors and crank the engine until you get good spray out of the lines. Then you tighten them down and start it up. It will run rough for a bit but it will go.

Edwin

Daviedoall

Fuel was squirting up 2 feet above the engine. I bled it 3 times. I like your idea of loosening the fuel return banjo. It's a check valve too that could be a restriction.
Since the new injectors have stopped the air in the return line I will tomorrow reassemble the Dura Lift in the tail section as original with the filter/water separator inline.
By presently bypassing the engine pump I don't have a fuel pressure pickup. The fuel pressure used to run 5 pounds with the Dura Lift, never more.
I like how the later pumps have an overflow right on top. I hope a big air fart comes out of that return banjo.! Thanks for the clues!

Daviedoall

Today I put the fuel system back to where I began. I put clear lines before and after the electric pump at the tank. The Dura Lift pump was blowing bubbles so I sidelined it and put on the spare electric pump. It sends clean fuel forward but only at 2-3 psi. When I spin the engine the pressure comes up to 5 psi due to the engine mounted mechanical pump.
Here's the strange part,,, I have bubbles coming out of the fuel return line with just the aft pump circulating fuel through the system. Still won't start but sputters every time. I bled the fuel at the filter exit banjo bolt, and also at the fuel inlet elbow into the injection pump. Also loosened the fuel return line banjo but got no big air there.
SO, how can air get into the pressurized side of the system without turning it over? Could the mechanical pump bleed air in at rest?
And, I have fuel shooting 2' up when the injectors lines are cracked to bleed them.
Life used to be simple,,, Why the *** whooping? I've never been broken down like this. Thanks for trying to help, it means a lot!

oliver foster

If you are still getting air the likely culprit is between the Lift pump that is sucking fuel out of whatever tank it is in.
Things like connections, the pick up tube in the tank, ETC are places to check.

oliver foster

Any progress on the problem?