1998 12 valve 5.9 cummins needs boost

[Kerry Bradley]

Will try not to ramble to much . I am pulling my 12,000 lb. fith wheel with this 1998 12 valve 5.9 cummins with auto transmission and having trouble on hills . I have a 24 valve 5.9 cummins that has no trouble what so ever . I want to up my boost on the 1998 to see if that will help . My max boost now is 22 lbs. and that is to the floor pulling the trailer up hill . Now I am unhooked from the trailer and have unhooked the rubber hose from the tee on the afc that runs to the wastegate . I plug the tee and the line to wastegate get 20 lbs. boost . Unplug line to wastegate 20lbs. boost . (did not think it would change anything ) . Unplug tee on afc and still have 20 lbs. boost . Why is my boost not changing when doing any of these things and am I barking up the wrong tree to get a little more power getting up a hill ? Thanks and hope this makes sense .

 

[fest3er]

Want more power? You need more fuel. Slide the AFC housing (I believe) all the way forward. Then back an 1/8 inch or so to control smoke. Then you'll likely need to increase trans line pressure to keep the TC clutch from slipping. (And you might need to change the TC to a multi-disk clutch unit.)

 

[GAmes]

20 psi boost is about right for a stock engine. The '98 12 valve with an auto is rated at 180HP. Your 24 valve is rated higher than that, plus it has a computer controlled injection system which is a lot more efficient.

 

[Killer223]

Your 24 valve is rated higher than that, plus it has a computer controlled injection system which is a lot more efficient.

can't agree with the more efficient part.
I have 3 Cummins powered trucks. 95 304K, early 04 250K, deleted 08 180K.
the 95 is by far the best at MPG's the 95 and 08 are manuals. and the 04 has a built auto from Fred Swanson. 08 and 04 average 16-18, 95 gets 19-22.

 

[NIsaacs]

The '95 is the lightest truck with the least amount of power....

Nick

 

[Kerry Bradley]

Thanks for you input fellows. I took the wastegate actuator off and checked it and it is bad . Can blow and suck air right thru . I guess bad diaphram . I put a light spring on the wastegate arm because did not want to just shut and lock it down to try it out . Changed and improved greatly and have 31 lbs . max. boost now . Now just need to decide which wastegate actuator to buy .

 

[GAmes]

can't agree with the more efficient part.
I have 3 Cummins powered trucks. 95 304K, early 04 250K, deleted 08 180K.
the 95 is by far the best at MPG's the 95 and 08 are manuals. and the 04 has a built auto from Fred Swanson. 08 and 04 average 16-18, 95 gets 19-22.

Disagree if you want, but computer controlled injection systems are scientifically better than mechanical. With a mechanical you are stuck at one timing setting where the computer control advances and retards it according to RPM and other inputs. Imagine an old gas engine without vacuum advance. Comparing the mileage of three different vehicles isn't much of a testament. My wife's Toyota gets 35mpg, so what?

 

[HHhuntitall]

20psi sounds normal. The timing retardation used on the '98 year trucks, plus the loss of power through your transmission sounds like it's doing what it was made to do.... we get spoiled by the later trucks and the power they provide. Some of the suggestions above sound like what I would suggest. A TC or a pump calibration. Or both.

Disagree if you want, but computer controlled injection systems are scientifically better than mechanical. With a mechanical you are stuck at one timing setting where the computer control advances and retards it according to RPM and other inputs. Imagine an old gas engine without vacuum advance. Comparing the mileage of three different vehicles isn't much of a testament. My wife's Toyota gets 35mpg, so what?

Politely, I must disagree. Timing is controlled by the injection pump setting, yes. But, the old VE's had both static and dynamic timing, and were a marvel of engineering. The P-pumps are only static, but can be calibrated to operate at an ideal rpm range. Scientifically, the electronic managed systems SHOULD be more efficient and dependable, given the advancements in electronics and materials. Statistically, the reality is the electronic systems are more prone to failure, and rarely get much better mileage, if they do. The results are all across the charts, with some getting 20-24mpg, and others 12-16. The higher compression ratios of the newer engines help with mileage, as well, but the electronic features of the injection system wear out quicker and fail at a much higher rate. HPCR injectors are known for their failures at lower mileage. How many p-pumped 12v's, even when bumped to equal the newer HPCR's HP rating, will run well over 300k miles with little to no repairs? I've never had a HPCR run that many miles without needing an injector.... or six.... The lowest bidder war comes at a cost... to us.

And comparing three different trucks is very relevant, when each has a different version of the same engine.... it's the progression (or regression) of technology.....

 

[GAmes]

Politely, I must disagree.

OK. I don't think many of your points are relevant, and I agree with most of them, but it is your prerogative to believe otherwise. My observation is that a computer controlled injection system will outperform a mechanical system when it comes to producing power across the power band. My 12 valve that is set up mainly for highway driving sucks around town at low speeds. A computer controlled injection system would do well doing both.

 

[Bob4x4]

Thanks for you input fellows. I took the wastegate actuator off and checked it and it is bad . Can blow and suck air right thru . I guess bad diaphram . I put a light spring on the wastegate arm because did not want to just shut and lock it down to try it out . Changed and improved greatly and have 31 lbs . max. boost now . Now just need to decide which wastegate actuator to buy .

Since you say you are now getting 30 psi and no mention of a cel,we must assume your truck is not stock.It may help to have a bit more truck info in a signature line to get more relevant responses

 

[Kerry Bradley]

I do not know what cel stands for so I can not speak about it at this point . Sorry , I am not up on all that . It is a stock engine and has been a daily driver for me since 2009 . Dodge owners will not like this next part . I just last year took this engine out of the 2wd dodge standard transmission that it was in and put it in a 03 F250 xlt with the 5r110 auto transmission . Thought it ran pretty good until hooking to my 12k fifth wheel . I even felt that when in the dodge pulling the camper it lacked a little especially when my wife's dodge/cummins 24 valve pulled it almost effortlessly . Yea , I know 24 valve and 12 valve different . Now I know I have had a problem with waste gate actuator and may have had all along . I will be pulling the camper again in a week or so and see what happens now with that problem taken care of . Thanks

 

[DavidC]

cel = check engine light

Dave

 

[Kerry Bradley]

uh huh ! no check engine light .