Surging when off throttle

[glaser06]

Ok, just like the title says. When I let off the throttle to slow down the engine surges up and down until I start applying the brakes. I have a banks turbo on my truck, I think it was doing this before the install but I can't recall for sure. If so, the turbo exaggerated the issue.

Any ideas as to what could cause this?

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[Truckyea]

Sounds like something sticking in the injection pump or cable


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[glaser06]

Sounds like something sticking in the injection pump or cable


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I was thinking IP. What cable are you referring to?

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[M1009CUCV03]

Throttle cable possibly

 

[glaser06]

Could that cause it to surge up/down, up/down, up/down every time I let off the accelerator?

It's not a one time kick in rpms like I would expect a stuck cable to do. It cycles until idle.

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[glaser06]

Ok, any idea how to test of if it's the IP or cable?

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[Barrman]

Try holding a steady 1,000-1500 rpm sitting still in park. Give it a blip and then get off the throttle. A failing IP will normally shut off in that situation.

 

[glaser06]

Thanks Barrman, I'll give it a try in the morning.

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[glaser06]

Tried it with motor warm. Not only did the motor not want to hold a steady rpm, the surging is worse now (very noticeable at hwy speeds) and it didn't die during the test.

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[Panici]

Was anything else changed when you put the new turbo in?

Do you have a fuel pressure gauge?

 

[glaser06]

No, nothing else changed. It's mostly a banks kit. Do you mean tool or mounted in the truck?

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[Panici]

No, nothing else changed. It's mostly a banks kit. Do you mean tool or mounted in the truck?

So it was a kit you used then, it had all the supporting parts needed besides the turbocharger?

Either a truck mounted or removable (tool) fuel pressure gauge would do the trick. If your surging corresponds to changes in fuel pressure, you've narrowed the issue.

 

[Barrman]

Sorry I jumped to a test when I should have asked first off if you have changed the fuel filter? Even if you have recently, do it again. Part of the filter change is basically a lift pump check out as well. When you unplug the pink wire, open the filter vent and turn the engine over until fuel comes out. There are several Youtube videos showing how to do this. Basically, if you don't have fuel coming out of the filter within just a few seconds of cranking. You have issues at the lift pump or all the way back at the tank and anywhere in between.

If that all checks out good. Then pull the IP fuel return line which has the red squeeze clamp holding it to the IP and remove the fitting it was attached to. It should be clear inside with a spring loaded glass ball that moves when you push it with a little bitty screw driver. Any black chunks or gunk in there leads us back to the IP.

 

[glaser06]

So it was a kit you used then, it had all the supporting parts needed besides the turbocharger?

Either a truck mounted or removable (tool) fuel pressure gauge would do the trick. If your surging corresponds to changes in fuel pressure, you've narrowed the issue.

It was a kit that had the turbo charger and manifold and about 85% of the supporting hardware and gaskets. I did change out the mechanical lift pump while I was at it, IIRC. Is there a pressure gauge port on these somewhere? I know the modern ones have a test port on the fuel rail, as do the Jeep 4.0L motors. I have a gas fuel pressure gauge (good to 100 psi) that I can test the lift pump with if there's a port, I assume the IP pressures are around 400 psi?

 

[glaser06]

Sorry I jumped to a test when I should have asked first off if you have changed the fuel filter? Even if you have recently, do it again. Part of the filter change is basically a lift pump check out as well. When you unplug the pink wire, open the filter vent and turn the engine over until fuel comes out. There are several Youtube videos showing how to do this. Basically, if you don't have fuel coming out of the filter within just a few seconds of cranking. You have issues at the lift pump or all the way back at the tank and anywhere in between.

If that all checks out good. Then pull the IP fuel return line which has the red squeeze clamp holding it to the IP and remove the fitting it was attached to. It should be clear inside with a spring loaded glass ball that moves when you push it with a little bitty screw driver. Any black chunks or gunk in there leads us back to the IP.

Thanks Barrman. New Wix fuel filter arrived yesterday, I run these checks today, weather permitting.

 

[glaser06]

Swapped out the fuel filter. Didn't sound promising even after I let the air run out of the system (idle and a couple throttle presses). I'll see how it does on the drive home today.

 

[glaser06]

Swapped out the fuel filter. Didn't sound promising even after I let the air run out of the system (idle and a couple throttle presses). I'll see how it does on the drive home today.

Well, the filter helped for a bit. Stopped surging when off throttle for a few days, but now it's back at it again. Parked the truck for now and driving the jeep daily for the moment. I did notice that after the filter was changed, I am still getting a surge around 45 mph. Basically, if I hold the pedal in one place it accelerates smoothly up to 45, then it feels like the pedal was mashed. Do these trucks have a pressure port for fuel pressure or will I have to go inline with a gauge? Any pictures will help, this is usually my daily driver so I try to fix it as opposed to letting it sit like some of my other projects.


Edit: When I changed the fuel filter, it took about 8-10 2 second cranks to get fuel out of the new filter. Don't know how that ranks for a new dry filter change out.

 

[richingalveston]

try changing the filter and see if that gets you a couple more days. if so, you got something in your tank that is clogging the filters fast.

if the filter is clean, I think you have a failing IP.

It is definitely a fuel metering problem, most of that happens in the IP. The fuel lines on the truck can starve the IP but normally not overpressure it.

your fuel tank and lines can cause the problem you are having and so can an IP that is failing. IF your lines and tank are good, you need to rebuild IP.

 

[glaser06]

To tell if the filter is clean, cut it open or just assume if I only get a few more days that I have trash in the tank?

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[glaser06]

While working today (and impatiently waiting on my next fuel filter to arrive) I found this: http://www.steelsoldiers.com/showthread.php?154108-Rough-idle-and-surge-after-turning-up-IP

Sounds almost exactly like what happened to me. Since I haven't located an easy place to check my fuel pressure yet, I'm going to give this a shot after the new fuel filter. Will check the fuel return line on the IP for trash as well.