Surging has me stumped

[asmith]

This issue has all the classic signs of air intrusion. But I cannot for the life of me figure out where it is coming from. I figured I would throw it out to the group to see if any sees something I am missing.

Trucks starts up nice and easy. It will run fine for 3-5 mintues then it starts bucking and surging like you wouldnt believe. the acceleration is amazing even with out touching the pedal. It will do that on and off for a few minutes then settle down, then randomly throughout the day while driving it will happen again. It is getting more frequent and the surging is getting worse, to the point where it died on me once while driving at about 20mph. My conclusion is I am getting air into the system somewhere. I have gone over the fuel lines with a fine tooth comb. Nothing damp any where. I should mention I have a completely redone fuel system. I have a big single rear tank filters and electric pump on the frame close to the tank and AN lines all the way to the IP.

I replaced the filters, and installed a new lift pump, still doing the same thing. It hasn't improved at all. My old pump was a holley blue with a regulator, I swapped it out for an air dog raptor that should be more than enough pump. My only thought now is something is wrong in the tank. I have over half a tank of fuel, but maybe there is a hole somewhere up high in the pickup and that is sucking air? What do you guys think?

Oh IP and injectors are less than two years old from CDD.

 

[Jesus Freak]

Maybe the factory fuel selector valve? Other than that, there's always the random pin hole on the sending unit in the tank...... have fun....

 

[Nero]

If it does it throughout the day, makes me think sticking timing... Have you tried running fuel cleaner through er?

 

[asmith]

I run hotshots everyday diesel additive in every tank. Do you think the IP could still be sticking? Do you have a fuel cleaner you like?

Is there anything else with the IP that could cause this issue? I really dont know much about them and if I should be looking at something with it as well as the fuel system.

 

[asmith]

Maybe the factory fuel selector valve? Other than that, there's always the random pin hole on the sending unit in the tank...... have fun....

The FSV is long gone. I only have the large single tank in the rear. Thats why this is so maddening. I wanted this to be a simple system with minimal places to have issues.

 

[Jesus Freak]

The FSV is long gone. I only have the large single tank in the rear. Thats why this is so maddening. I wanted this to be a simple system with minimal places to have issues.

These engines are committed to sucking air. It's kinda like livestock pens and housing, they will show you your weak spots......

 

[Nero]

I prefer power service, but if you run cleaner that often, probably isn't the issue.
You could install a diag line between the filter head and injection pump, clear tubing to check for air.

 

[DirtyWood]

Aren't there o-rings in the female quick connect fittings? Bad o-rings?

 

[asmith]

Aren't there o-rings in the female quick connect fittings? Bad o-rings?

True. Those connections are not wet, but that is a good point. I wonder if they can be changed out just in case.

 

[ROCK HARVEY]

It sure sounds like you’re sucking air. For that to be the case it has to be happening before the fuel pump, because everything after that is pressurized with the pump running. I would pay special attention to the fuel filter connections, and make sure the filters are spun on tight. Hopefully it’s there and not inside the tank, which would be more of a pain.

 

[ROCK HARVEY]

To add to Nero’s suggestion, you could just run a long clear tube from the output on your fuel pump back to your tank and let it run for 20 minutes to see if you can see air bubbles. That would confirm that you’re sucking air somewhere.

 

[trancas]

Look for tiny bits of debris in the return line holes in the injector caps. I had some deteriorated return hose specks from the pump cover to the injector caps, and it sure had me stumped.
Same symptom.
Thats when I replaced all the hoses with barrier hose. They'll last 10 years now