Fuel Economy Mystery
 

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

You could try doin valve lash?? If its never been done then its definatly time, Im an american so KM dont mean anything to me, I got about 725 Miles out of a tank so thats 22 Miles to the gallon for me. But I was getting 17 at best and I was not happy and I had 212K Miles on my truck so I did valve lash I have better power and better fuel economy.

heres the procedure takes about and 1 to 2 hours depending how stingy you are..


24v standard procedure - valve lash adjustment
________________________________________
NOTE: To obtain accurate readings, valve lash
measurements AND adjustments should only be
performed when the engine coolant temperature is
less than 60° C (140° F).

The 24–valve overhead system is a “low-maintenance”
design. Routine adjustments are no longer necessary,
however, measurement should still take place when
troubleshooting performance problems, or upon completion
of a repair that includes removal and installation
of the valve train components or injectors.

1. Disconnect battery negative cables.

2. Remove cylinder head cover

3. Using the crankshaft barring tool #7471–B, rotate crankshaft to align damper TDC mark to 12:00 o’clock position.
a. If both number one cylinder rocker levers are loose, continue to next step.
b. If both number one cylinder rocker levers are not loose, rotate crankshaft 360 degrees.

4. With the engine in this position, valve lash can be measured at the following rocker arms: INTAKE 1–2–4 /EXHAUST 1–3–5. Measure the valve lash by inserting a feeler gauge between the rocker arm socket and crosshead.

5. If adjustment/resetting is required, loosen the lock nut on rocker arms and turn the adjusting screw
until the desired lash is obtained:

INTAKE 0.254 mm (0.010 in.)
EXHAUST 0.660 mm (0.026 in.)

Tighten the lock nut to 24 N•m (18 ft. lbs.) and recheck the valve lash.

6. Using the crankshaft barring tool, rotate the crankshaft one revolution (360°) to align the damper TDC mark to the 12 o’clock position.

7. With the engine in this position, valve lash can be measured at the remaining rocker arms: INTAKE 3–5–6 / EXHAUST 2–4–6. Use the same method as above for determining whether adjustment is necessary, and adjust those that are found to be outside of the limits.

8. Install the cylinder head cover

9. Connect the battery negative cables

1 mile = 1.6 miles.

1 gallon = 3.79 litres

725 miles = 1160 km

Thanks, glad you better at that conversion stuff than me..:tu:

I'm going to do this lashing on the weekend.

I appreciate the input my man!

Hope it helps you out!!!! did alot of good for me! let me know if it made a difference.

Definitely going to have to try this out! My 01 is basically the same as yours, except a few more km (400k) and I have 4" straight pipe. I get on average 700K to a tank. Glad to know I wasn't the only one thinking this was a bit off.