Strange surging

[Mherriford]

So i recently got my idi back on the road it was down for some sheet metal swapping.

If I am cruising at a steady rpm without the accelerator pedal moving, or any other input form me changing the engine will lightly surge.
I can watch the boost gauge gain about 3 psi while this happens, if I let off the pedal slightly the boost will drop back down to where it was before the surge. If I keep my foot I it and keep the boost high, no surging.

Truck has 106000 miles, I know the injection pump has been replaced once, no idea of when though, no idea about how many miles are on the injectors, or the turbo, which is an ats.

Any idea on things I could check? This does not seem to be a catastrophic problem, but I would sure hate for it to develop into something bad, I looked and have not seen anything different around the turbo, no loose connections that I can see,

Any ideas?

 

[79jasper]

Air intrusion.

Sent from my SAMSUNG-SM-G935A using Tapatalk

 

[Mherriford]

As in an air intrusion into an injection line?

 

[79jasper]

Fuel line.


Sent from my SAMSUNG-SM-G935A using Tapatalk

 

[83ford]

Have you changed your fuel filter? Mine was full and wouldn't let me get enough fuel so I couldn't ever see my caps leaking till I put a new filter on which fixed the surge


Sent from my Iphone using Tapatalk

 

[Mherriford]

I do have a new filter sitting here, I will throw it on.

And 79jasper, your talking g about something pre injection pump, so somewhere between the hard line, e pump, filter head, and the supply line to the ip

 

[79jasper]

Correct, but even all the way back to the tanks.

Sent from my SAMSUNG-SM-G935A using Tapatalk

 

[mblaney]

Yep, air getting into the fuel supply or fuel flow is restricted. I would think your "fuel filter" idiot light should be coming on or at least flickering.

Here are some tests you can do:

Air intrusion: Remove the fuel pressure sender (1/8 NPT) and install a clear line (Tygon or vinyl). Pull a slow vacuum (siphon) and watch for air bubbles. This will verify if you have air getting in anywhere between the pickup in the tank and the filter head. If you have air, work backwards... pull fuel from the supply line at the filter, etc until you isolate where the intrusion is.

I would also do a flow test; assuming you have a mechanical supply pump you will have to crank it but after checking for air intrusion. Disable the IP (unplug fuel shut off solenoid) crank it over and make sure you have good fuel flow using the same hose installed at the pressure sender port.

Pressure test: Flex or crush the vinyl hose over for back pressure, does it spray nice? Do you have a pressure gauge for checking ATV tires? You can use that to check pressure at the filter head schrader fitting.

 

[BDCarrillo]

Yep, air getting into the fuel supply or fuel flow is restricted. I would think your "fuel filter" idiot light should be coming on or at least flickering.

That light is driven by a vacuum sensor, so if air is being forced into the fuel system it'll still maintain a positive pressure, thus the light won't trip.

 

[icanfixall]

My thoughts are you have a fuel restriction in the filter. Good idea is change it and test it ..

 

[83ford]

Another thought after you change the filter check out the selector switch. Had to replace mine twice I think now and that's how it acted. You could jump around it so it pulls off one tank for awhile and see if that fixes it


Sent from my Iphone using Tapatalk

 

[Mherriford]

Ok a quick update, I replaced the fuel filter tonight, and also found that the rubber line from the hard line to my carrier pump had a kink in it. So i replaced that and added an elbow to make the corner without future issues, will see how it behaves tomorrow and will let you guys know.