uncleroty

Hey guys, I have a problem with my truck, and I wonder if anyone could have a potential diagnosis for it.

The truck starts and runs normally, no smoke or anything, but when driving I suddenly lose power if I let off the throttle, and have to shift down to kick the rpms back up. Once accelerating she drives well. As soon as I let off the throttle at about 80-90km/hr she loses power and can barely maintain that speed. Problem is particularly bad going up hills.

When in park, she idles well and throttles up with no hesitation. At a certain point in the rpm curve she bogs down and then jumps up with no movement of the throttle.

I actually thought it was a sticking valve in the tranny until I noticed the problem with the truck in park.

Lift pump has been changed, new fuel filter etc.

I'm a bit puzzled, any ideas?

Nuttymopar

Not sure but when was the last time you change your fuel filter?

Is the Throttle linkage sticking at all? Test from inside and also at the linkage itself to make sure it isn't binding anyplace.

Bad injectors somewhere?

uncleroty

I did the fuel filter a short time ago in response to the problem, I'll give the linkage a check, as it had bound up in the past.

Do you think a good run of injector cleaner might help? I wouldn't think it was the injector itself as it runs well in several rpm ranges, but I could be wrong.

Any other ideas of what to look into? I have it for my weekend project.

Nuttymopar

Air clogged? but wouldn't think so.

I wonder about a electric short somewhere on the fuel selenoid or something. It does seem strange that even in Park it will rev up some and then drop. Almost like a electrical drop of some sort until you get the rev's back up to make that connection?

JD730

I don't think this is the problem because of your in park test(little or no boost with no load reved up), but this sounds like the pin that contacts the AFC cone in the pump is sticking. Driving along at speed with boost, let off now no boost pin rides back on AFC cone when it comes up. Now you back into the throttle and its sluggess because the pin is stuck at a low boost setting when your accerlerating.

But this puzzles me. Maybe a sticky governer. Throttle shaft getting hung up on something? Full travel of the thottle?
Running a good dose of cleaner won't hurt anything.

uncleroty

I have full throttle travel, and it does not appear to be binding. What you're saying with the afc/pin sounds like a possibility. Is it hard to do? I have the manual, but I'll have to check if there is any way to test that. Can you replace it without replacing the whole thing?

The governor? maybe too.

Any other advice on how to check into this would be appreciated.

gman07

I had a problem with mine one time too. It was a while ago (before I found this site) and it turned out to be something broken in the pump that fed metal through the injectors. We ended up replacing the pump and injectors (unfortunately with stock ones). I doubt that is your problem, but I would check the injectors. I also had a problem with the truck not idling right and dropping RPMs sometimes in Park/Neutral that went away when I installed a 3200 RPM spring. If you have someone to help, the governor spring is a cheap, easy mod that might help with your problem.

Alec

THe AFC would give you reduced power, not no power. It sounds like your injector pump is dying. I am sorry to say that, but it sounds like a worn governor shaft or maybe broken return springs on the cam.

G1625S

I'm with Alec on this, I'm afraid. Sounds like the pump is tired. Even though the lift pump is recent, try and get a pressure reading just for kicks. Also, maybe pull the fuel filter, drain it and fill it with 1/4 diesel and 3/4 diesel treatment of your choice---something that helps lubricate things---maybe she's just a bit gummed up, ya never know.

tboling

Sounds like to me the fuel pin that rides on the diaphram pin is sticking. I have had many trucks come to me with this problem and sounds like what yours truck is doing. Remove the afc top and remove the diaphram spring and seal. Use light so u can see down in the afc housing and pull the throttle wide open and see if the pin comes out it should almost hit the other side. If not spray wd 40 or liquid wrench on the pin and keep pushing it back in with a screw diver and working it out with the throttle. Un tell it comes out like it should then push the pin back and reinstall the diaphram. Do all of this with the engine off of course. Good luck