Idle creeps up while in park after engine warmed up

[shotty]

After the engine is warm, placing the truck in park results in the idle slowly creeping up a few hundred RPMs. When the engine is cold it doesn't do this. I've been told this is a sign of air leaking into the IP. Considering when parked for a little bit there is air coming out the return line from the IP I believe it. I was wondering if anyone else has had similar symptoms or any input before I replace the IP.

 

[Gunfreak25]

Why replace the injection pump? Does it have any other issues? Does it run, start, perform normally? Considering the pumps are usually around 10 psi internal housing pressure they dont really suck in air. They do however leak fuel out the throttle shaft and advance piston plunger seal at the bottom passenger side of the pump.

If you have air entering the system the most common point is leaky fuel return hoses.

The factory engine mounted lift pump sucks fuel from the tank, so you know anywhere from the lift pump backwards can be sucking air somewhere.

If you have a frame mount fuel pump close to the tank, most of your fuel line is now under pressure instead of vacuum which makes finding air leaks easier.

Air leaks without fuel leaks happens. A lot. After I replaced my entire system I traced the last air leak to a cracked fuel pickup tube i side the fuel tank. It happens!

Sent from my SM-G955U using Tapatalk

 

[dougco1]

After the engine is warm, placing the truck in park results in the idle slowly creeping up a few hundred RPMs. When the engine is cold it doesn't do this. I've been told this is a sign of air leaking into the IP. Considering when parked for a little bit there is air coming out the return line from the IP I believe it. I was wondering if anyone else has had similar symptoms or any input before I replace the IP.

Is your high idle/ timing advance switch functioning properly? Sometimes that will speed-up/race your rpm when/if it acts up. To test, just unplug it after start up see if it changes your rpm speed.

 

[shotty]

Is your high idle/ timing advance switch functioning properly? Sometimes that will speed-up/race your rpm when/if it acts up. To test, just unplug it after start up see if it changes your rpm speed.

It's working fine. Once the truck starts idling high, engaging the solenoid makes no difference. I can even give it a bit more throttle than the solenoid would and it still doesn't change the RPM.

After staring at my clear return line on the IP for a few minutes that I get very tiny air bubbles from the injector side of the return line. I'm sure if I watched it for awhile I would see most of the air that accumaltes there coming from that side, so it's probably the injector return lines. I ordered a kit because it's cheap and easy to rule out. If that doesn't fix it I'll look into pressurizing the system to find the leak.

 

[sandcobra164]

I just replaced my injection pump but did alot of research prior to tackling the job. The fuel system is under pressure at every point past the lift pump on the passenger side of the engine block. It is possible that the lift pump can draw some air in but that should be taken care of by the design of the injection pump and result in air bubbles coming out of the housing pressure regulator and show in your clear return line. It would take quite an intrusion of air to make it to the booster pump inside the injection pump to show up in the injector return lines. They are under pressure as well so a leak of fuel would show up on them if they were questionable. If the truck is not loosing prime, I'd rule out the tank to lift pump connections. How does you're truck operate otherwise? The part that I'm concerned about is that if you apply more throttle than the cold start solenoid would provide, you claim it makes no difference. On my truck, a 1/4 inch of the throttle pedal results in about 2,000 rpm in neutral. Mine does idle higher in neutral than park but I attribute that to no additional throttle input and placing the truck in gear results in a load placed on the engine.

 

[shotty]

The truck starts and runs fine, however after sitting awhile there is a small 1/4-1/2 inch air bubble in the clear return line. This doesn't impede starting at all though, like it did when I had a loose line going to the fuel inlet of the IP. That caused issues with starting and would cause a fast idle period shortly after starting. Driving the truck is fine too, nothing erratic or unexpected. Once I shift to park it slowly speeds up the idle though. If I move the plate that the fast idle solenoid presses against when engaged, I have to move it at least 1/2 inch or more before the RPMs increase.

I've been looking through all the TMs and cant find a diagram that shows the return line routing. I'm assuming the fuel from the IP and injector returns flows back to the tank, but if that were the case then having an air leak in the injector return lines wouldn't matter. I could see it being fed back to the inlet of the pump though, which would certainly cause issues. I guess I'll just have to put on my big boy pants and go outside in the cold and look a bit closer than I did earlier

Not sure what's going on. There's certainly a problem somewhere though. I just remembered that a few weeks ago I started the truck after it sat for a few days, and some fuel spilled out of the intake valley and drained out down by the transmission. Hasn't done it since and I couldn't find a leak then.