Engine/Transmission (1998.5 - 2002) Poor MPG

[_BSharp]

Gentlemen,



I have a 98. 5 24v all stock and standard barring a Banks exhaust w/power elbow. I have been avg. 18-19 highway, 14-15 towing (on highway) and on a recent trip dropped down to 11 MPG towing on the highway. Any suggestions on what is going on?



Thanks!

 

[Beast2B]

Welcom to TDR!

Fuel seems to be one of the most common cases. Whether it's the electric fuel lift pump dying or a clogged fuel filter, a fuel pressure check going into the VP44 injection pump should tell.

 

[tractorface]

Wow big drop. Did you notice any performance trouble? Could you have a big fuel leak? I can not imagine a drop that large without you noticing something else. Is it possible that you mis-calculated?

 

[sslechta]

Funny story. I had something similar happen recently. I always calculate my mileage by hand and I noticed by the trip odometer that I had not put the usual miles on to be that low on fuel. Anyway, I fill up and calculate the mileage and about had a heart attack when it came to just over 12 miles to the gallon. Every possible thought ran through my head trying to figure out what could be wrong (I am consistantly getting right at 16 in town driving). Then it dawned on me - I had changed the bateries since I last filled and it must have reset my trip odo. Dooohhh!!! All tanks since mileage has been normal...

 

[Beast2B]

I also recall any of several sensors causing issues: IAT. MAP, cam position sensor...

Maybe a visit to a shop with a good code reader can help diagnose.

 

[rkressg]

Winter blend fuel will cause a 2-3mpg loss of fuel economy. Other main causes for poor fuel economy are:

1. IAT

2. MAP

3. Clogged fuel filter

4. Bad injector



Depending on the mileage, changing the IAT will usually result in the most significant mpg gain (depending upon your driving characteristics).

-Rich

 

[_BSharp]

Thanks for the feedback guys. I changed filters/fluids and also checked my fuel pressure. Lift pump is bad. I am making 7psi at idle and 2-3psi driving. I am having an FASS installed tomorrow morning!!! Had a diagnostic check and everything else seemed to be fine. Hope this all works out well.

 

[CEdwards]

BSHARP Did you have any problems with the way your truck ran because of your low fuel pressure? I am in the wrong forum here but i am having similar problems. mine sometimes takes a spell of running rough or dying. I have already checked and replaced and cleaned every conceivable thing to fix that problem, but my mileage has also dropped and i haven't checked my fuel pressure yet. mainly because their are no good diesel shops around here and i don't have what i need to check it. I think I ran across something on here somewhere where i could order the kit to check fuel pressure. Did you check it yourself or take it to a shop? thanks for any info, I really appreciate it. by the way what is the IAT?

 

[Beast2B]

IAT = Intake Air Temp. 24v trucks have several parameters monitored for the ECM to determine fueling and timing. MAP (boost), CPS (cam or crank postion sensor) among others

 

[DieselMinded]

sounds like the Lp was dieing @ 7 psi I wouldnt say it was bad 0 is bad I had 8 psi and I never changed the LP I added a pusher and now I have 15psi . been like that for 10,000 miles no problem



Id say the LP had nothing to do with you losing fuel milage

DM

 

[_BSharp]

you can get a fuel pressure test gauge at www.smokindiesel.com



$35 shipped

 

[jeepit]

Where is IAT located and can it be cleaned or just replaced?

 

[TDiston]

I May Be Having The Same Problem. What Are The Better Lift Pumps Out There? I Know Of A Few. Which Did You Use.

 

[DieselMinded]

Carter avalible in kit for at EEp



http://www.enterpriseengine.com/



$165



DM



call them and talk to Doug