Hey everyone!

I recently purchased my first cummins and couldn't be happier with one exception - the fuel economy.

I realize that a truck is a truck, and hoping for 'good' fuel mileage is pissing into the wind, but something seems up.

I have a 1998.5 5.9 24v. 220,000 kms. Auto (Fresh rebuild)

Levelling kit
33x12.5 BFG M/T's
3" Straight pipe exhaust

I recently replaced the fuel filter, oil, air filter, and ran some diesel treatment through the engine.

I'm averaging about 6 km / 1 L, and if I'm lucky 700 km to a tank.

I have 4 close buddies all with the same generation motors who are running 35" tires and they all average between 800 and 1000 kms a tank.

I know my speedo is out by about 17% (100km/h is actually 117 km/h) and have factored this into my calculations.

I run Howe's Meaner Power Cleaner with each tank and never run it passed 1/4 tank, so I'm not sucking sludge into the filter.

I drive it like a little old man, so driving style shouldn't be the issue.

It drives great, doesn't seem to be lacking any power and has no apparent issues, but I know this vehicle is capable of more.

Currently I'm thinking injectors or injector pump, but I'm still new to this so I was hoping you guys might have some idea's or directions to look in.

Thanks everybody!

- Drew

 

what lift pump is on your truck? Do you have any gauges? You could have low fuel pressure thus killing the injection pump would lead to poor fuel mileage. I am not familiar with the fuel additive your using so you can always try not using it for a tank or 2 and see what happens. Also found that for best mileage in these change the differentials over to synthetic gear oil helps.

 

if over 100k do and overhead .also clean the MAP sensor

if you have a boost gauge watch it or look at it as a work gauge..the higher the boost the worse the milage....I can start out and get to 65 mph without going over 8psi boost

 

No gauges, I'm investing in a Juice w/ attitude in the near future, so that will cover those bases.

I'm unsure of which lift pump I have in mine, reccomendations?

 

maybe look into a valve adjustment too.

 

you need something better than stock I really like Fass systems myself. something to keep it at 16psi would be a good thing. get that edge fast so you know fuel pressure or your going to spend 1k for a injection pump with no installation or anything