Max boost varies-- normal?

[Jim Sisson]

If you don’t get full throttle, you can’t produce full manifold pressure. And it doesn’t need to be that far out of adjustment. Just a thought Josh. It is where I look first. Although I had an 1983 F-250 Diesel, NA and now drive a 2005 6.0, my experience was with CAT engines and big trucks. Lots of things are similar.

 

[The_Josh_Bear]

If you don’t get full throttle, you can’t produce full manifold pressure. And it doesn’t need to be that far out of adjustment. Just a thought Josh. It is where I look first. Although I had an 1983 F-250 Diesel, NA and now drive a 2005 6.0, my experience was with CAT engines and big trucks. Lots of things are similar.

I'm not doubting your expertise but rather I cant wrap my brain around how the engine wiggling with torque an inch or two would affect the throttle cable. Its bolted to the intake manifold, so its position relative to the IP wont change even if the engine rocks all over the place, as I understand it.

I don't know how to test for worn mounts, mine look ok but I know for a fact that it rocks pretty good in 1st and 2nd gear at WOT, especially towing.

 

[Jim Sisson]

Have your foot feed depressed to the floor and go to your throttlesshaft and try to move get it to move further. You don’t have to have the engine running. It may have no effect, but at least you have eliminated that as an issue. I generally worked with throttle rods, so a cable may be different. Motor mount insulators just wear out and create a place for movement of the engine when it torques under a load. Jack up your engine and see f there is some play or movement. We used to consider ourselves lucky if we got a year of life out of the rear motor mounts on a KW or a Peterbilt powered with a 3408 CAT engine in our Log Trucks. We ran one at about 650 hp for about 10 years before we rebuilt it. But we changed the motor mounts often.

 

[Macrobb]

Have your foot feed depressed to the floor and go to your throttlesshaft and try to move get it to move further. You don’t have to have the engine running. It may have no effect, but at least you have eliminated that as an issue. I generally worked with throttle rods, so a cable may be different. Motor mount insulators just wear out and create a place for movement of the engine when it torques under a load. Jack up your engine and see f there is some play or movement. We used to consider ourselves lucky if we got a year of life out of the rear motor mounts on a KW or a Peterbilt powered with a 3408 CAT engine in our Log Trucks. We ran one at about 650 hp for about 10 years before we rebuilt it. But we changed the motor mounts often.

The good news is that our throttle cables won't be affected by motor mount issues. I... um... forgot to install the nuts on one motor mount; you could see the entire engine tweak up(by the movement of the gearshift) on acceleration. Throttle was fine though(as expected).

The cables, however, do stretch and loosen over time. Making sure that the throttle maxes out is definitely a good thing.

 

[Jim Sisson]

Every once in a while I get to help, even if it’s by accident.