1998.5 24v seems slow

zackmx said:

I am new to the cummins motors just got a new to me truck with 150 000 miles and it seems super slow. * * * It makes about 35psi fuel pressure and runs around 20lbs of boost if im really honking on it.

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1st problem, as I've mentioned in other posts, is the piece-of-junk Bosch VP44 injector pump that all 1988.5 thru 2001 ISB Cummins trucks come with -- if it hasn't failed yet, it will. The problem is a poorly designed computer that can't handle heat & vibration. However, the VP44 was upgraded for Frieghtliner as they use the same pump in the "Sprinter" vans sold under their nameplate & also by Dodge & Mercedes. Those vans come with a Mercedes V-6 diesel so the new pump has to be recalibrated for the ISB Cummins & I got mine from Blue Chip Diesel in New Hampshire -- the Dodge dealer does not have / cannot get the upgraded Frieghtliner version.

Next item is that the "lift pump" doesn't need to be putting out but 8-9 psi although 15 psi is better & that's what mine runs -- it's an upgraded replacement for the stock lift pump. An ISB Cummins will run with no lift pump @ all, it just keeps the VP44 injector pump from working as hard to pull fuel from the tank, but higher pressures do not make things better -- it's volume / flow that matters there, not pressure. Given the same size lines/fittings, etc. pressure & flow are diametrically opposed -- when one goes up the other goes down.

Next item is I got the Edge boost elbow for $27 & it "tricks" the wastegate so it opens later & slower, giving you more boost & sooner. Typical is jumping to 28 lbs. of boost then settling down to 25. New "neck" from intercooler hose to intake manifold is next.

I don't know what gearing you've got or which transmission, but my '98.5 with the new top-of-the-line Frieghtliner VP44, boost elbow, free-flowing exhaust I made, K&N air filter in the stock airbox & 4.10 gears will run off & hide from the vast majority of pickups, gasoline or diesel -- most passenger cars too. I didn't buy it to go drag racing, I ordered it for heavy loads & trailer towing, but with no load it'll flat scoot! And after the new pump & boost elbow install I even surprised myself!

Blue Chip also makes a "tuner" that'll give you 100 more HP @ the rear wheels, but that's an $1100 expense I can do without. If I can afford to get it in the future I will, but the truck has plenty of power without it, with fuel prices as high as they are I'm not willing to give away any mileage & it's actually a little better now than when I bought the truck new.

1998.5 cummins Diesel turbo 24 valve 3:55 rear end.

I do not know what pressure is except my tires. I burn no. 2 diesel and my truck will scat. I do not know what it will do in the quarter because as said before, it is not a race truck. But it will come in on the interstate and be up to 65 very quick to merge into traffic. I have a 28 ft. fifth wheel 2005 Prowler which can be 9500 gross weight. When I hook it up, it will squat 1.5 inches and pulling it up hills, it does not know it is doing anything. Very good truck. bought it used with 111000 and now it has 134000. It is 2 wheel drive. Has plenty of power for me. No issues with engine except the two wires coming off battery going to transmission would not let it find overdrive. Found out it was the batteries when it would not start, and corroded up all the time. Put two batteries on it and have not had any trouble. Had starter rebuilt and it was good to go. Love it. Wife does not like the noise, but I love a diesel. Had a 93 Ford 250 with the 7.3 the first year of the serpentine belt and no turbo. It would pull a house with 4x4 but the Ram rides alot better. I would say the 3:55 rear end has alot to do with my fuel economy and quick get up and go.