For a long time I have been losing power in the low end. It used to pull like crazy, but now it starts at 1800 vs 1200 rpm. It used to top out at 2800, now it is 3400 rpm. I have no smoke at all. I have checked most everything, but it all comes up ok, and I cannot find the problem. I get the feeling that it is not fueling up properly, but I can't find out why. I am starting to point my finger at the IP, but before I get into it, I want to be sure. Thanks.

 

Did you check your timing. I know alot of ppl say the timing slips on the p pump. I cant really see the pump dieing they are almost indestructable. Im shure someone else will chime in with more info but i think it might be slipped timing.

 

I had the timing checked a long time ago, when I first started to notice the problem. The mechanic said it was 12.5, stock. I can only assume that he knew what he was doing, and I am not positive of that. This has been a very slow process.

 

Have you checked fuel pressure or changed the overflow valve?
Don't assume the OF valve is good just because it's not that old, I've ran into several that have failed in just a couple thousand miles.

 

I have replaced the overflow valve about a year ago, and at the time, it seemed to help a bit, but did not solve the problem, or stop the continuing loss. I have replaced the lift pump, and checked pressure, only standing, not driving. It is 20-24 psi. I still can hit 25 lbs of boost going up a hill.

 

Make sure the boost line isnt bad/leaking going into the AFC housing on the pump. if it is, you wont get full fueling. I dont undertstand how/why you could be turning more rpm's though?? Possibly a governor problem?

Eric

 

That is one of the first things that was checked. My first "mechanic", I have been to three now, tightened it up, put on a adjustable boost elbow, cranked it down and declared the problem fixed. From that and a bunch of other sloppy work, I don't use him anymore.

 

Have you tried re-adjusting valve lash? What ever happened with the experiment of trying fuel from a seperate can? the 3400 vs 2800 and 1800 vs 1200 rpm is starting to sound more like the injection pump OR something feeding it (such as boost pressure or afc adjustment). It's interesting to note that both are a 600 rpm difference... is the tach reading correctly? Was the governer spring replaced at the same time as the fuel plate? THE GOVERNOR SHOULD LIMIT MAX RPM. Does it sustain the 3400 rpm? Might be worth a try swapping the injector nozzles with another set (if you can borrow some) but that still doesn't explain the rpm difference.

 

Go for the simple fixs first. The fuel heater has a screen in the bottom that just about nobody bothers to replace. They collect moisture and algae, rust and just about close the fuel flow. The other thing to watch is the electrical connection on the fuel heater, the insulation cracks and allows it to draw air and that will cut power significantly. If your flexible hoses between the frame and engine, and between the tank and frame are more than three years old, they should also be replaced as they develop microscopic air holes and will cut power long before they actually leak enough to stop the engine.

 

I checked the boost line,and it seems to be secure. There is another line that goes from the AFC to the pump, and I wonder about that. What does it do?
I have replaced the lift pump, and put in a rebuild kit for the preheater screen. It seemed OK, but it is a cheap fix, so I went ahead and did it. I checked the electrical connection and the plastic "disc" as well since I had everything on the bench. All rubber hoses have been replaced. I have a clear filter in-line to watch for air, as that has been a huge problem, but now I have it under control.
Valves have been adjusted twice. I did use the separate fuel can, and it was great for purging air out and getting the truck started from some other work I did, but I did not drive with it. The 600 RPM difference is just a general statement, it is not exact. It will hold 3400 @ wot in the driveway, makes the neighbors unhappy.
The governor spring has not been touched at all. The truck had a #8 plate in it when it started to lose low end acceleration. I changed it to a #10, but did not mess with the spring or the lever. I did not know anything about them at the time, and am now just learning about them. The plate change did not do much of anything.
It is interesting to realize that this has been a very slow process of decline, we are talking years since I first noticed the change, and that is why I now have more gray hair. Because of the long time frame, I get the feeling that something is slipping, vacuum leaking, or somthing mechanical failing. As one mechanic said, " the engine itself rarely fails, they are great engines, it is useually something around the engine that is the problem." Just have to somehow figure out what it is.