Surging/hesitating

[Miklos]

Truck is a 92 w250 auto with 150K on it. The only engine mod is 3.5" FLowmaster exhaust from the downtube back.

While driving at a steady speed, the truck will hesitate, then surge, hesitate, then surge over and over again. When accellerating, it runs as smooth as can be. It starts easy and runs great otherwise.

Changing the fuel filter had no effect on the problem. It is not connected to a certain tank of fuel either, as the truck has been doing this over the last several thousand miles.

What do I check next??????

[CumminsPride]

I would say IP.

Wade

[dpuckett]

Try tightening the AFC spring tension (turn starwheel up). I realize your engine is stock, but that would be a good place to start.

If that doesnt work, it may be time for a refresh. Unfortunately, low miles are no guarantee of a good fuel system.

Daniel

[Miklos]

I would say IP.

Wade

I am under the assumption that a weak injector pump would also cause hard starting. But the truck fires right up. Is this assuption incorrect?

[cummins king]

check the lift pump it could have somthing to do with it

[Underpsi]

Check for air leaks, people use different words to describe the same or different things. So try plumbing in a piece of clear line and see if you can see bubbles in it. the closer to the injection pump you can do it the better then you just go back from there and try and elimitate things like the lift pump, steel lines or fittings

[cummins king]

thats right my truck does that at idle but it will never stall
its an air leak that goes into the line and not out its probly between the tank and the lift pump thats were mine is if it was after the lift pump it would leak fuel

[CumminsPride]

I am under the assumption that a weak injector pump would also cause hard starting. But the truck fires right up. Is this assuption incorrect?

Not necessarily. I have a skid steer (perkins4x1.08) that will fire right up but once she's hot the injectors are getting weak pressure. The cold pump will spit fuel over the head across the engine compartment. A warm pump won't even get it over the head!

You are suggesting that there is surging at givin speeds. Is it in all gears and just a givin rpm or is it only in one gear?

It may not be the IP but I'd say put a fuel pressure guage in on the LP and see what your idle and WOT psi's are first. If the pressures are good then I would say IP.

Wade

[Miklos]

Hmmm.... before its fully warmed up, it doesn't seem to do it.

So what are some on-the-truck tests for the injector pump? I hate to just start swapping out $800 parts . Are there shrader valves for testing lift pump pressures like on my '01?

What makes this harder for me is this truck is my wifes daily driver.