Mileage Dropping

[Des]

I've been noticing that my mileage has been dropping over the last several thousand miles. I used to average between 17 and 19 mpg depending on the amount of city driving I did. I recently took a trip down to Laredo for a week or so and my average mileage for the trip was 14. 5 mpg. What a drop. The highway speeds were between 60 and 70 mph the entire trip (except through Austin). There was very little city driving. I've traveled this route on other trips to Laredo and other destinations and my mileage is always higher. Does anyone have any suggestions? The truck runs as good as ever and everything on the engine is stock - no adjustments to fueling. The only thing I have ever done is adjust the valve clearances and I did this sometime back. Is my timing off? Help!!

 

[GOakes]

You didn't say what method you are using to get mileage numbers but if it's a spot check (now and then) I would suggest you check every tank for the next five or so fill-ups and average them ... If you haven't been averaging a series of fill-ups your truck may be doing what mine "seems to do" i. e. one tank checks out at 13 to 16 and the next 21 to 24. My five tank averages running the 55 mph back roads of Trinity County Texas plus some 70 mph interstate and a lot of "Jack Rabbit Starts" is 19. 5 summer and 20/21 in cool weather. If the mileage you checked was based on at least three fill-ups then it sure sounds like you got a problem. If you don't have boost pressure and exhaust temp gauges then you are missing a really great diagnostic tool. I don't have the data to prove it but my gut feel is that watching those two gauges and reacting to the information could improve solo mileage by perhaps five percent and towing by several times that percentage. Then again that's just a nother don't know noth'in for sure Texas Bubba runn'in his mouth.



Sorry about all that verbiage --- it take me more words to say less than most folks



Old lonesome George



Yeah, I got a Dodge Pick-up --- it's a 97 model with B 5. 9 -- TST -- Boost pressure / exhaust temp / automatic transmission temp. gauges --- Sun Coast Prolok Converter --- 4 X2 --- 3. 55 --- Lot's of fun to drive with my trailer in tow --- of course my need to "run with the tall dogs" is cause for some smiles down at the diesel fuel store...

 

[BCFAST]

Ambient temperature has a lot to do with it... . hot air wont make power so the engine works harder to move the mass down the road. You may wanna think about a valve adjustment! I always get 20 (combination driving) and 23mpg (highway) and I NEVER turn the a/c off... it's freakin' hot!!!

 

[illflem]

It could be that when you're on the open highway that you might be flooring it more to pass than when in the city. A heavy right foot will drag down your mpgs more than most engine problems.

 

[Missouri Mule]

Des,

Have you checked for fuel leaks?

Have you had your fuel lines replaced?

Check hoses from turbo to intake make sure no holes and clamps are tight.

Check fuel tank and all fuel lines( if no was answer for second question) leaks.

I think fuel line leak most likely if they have not been changed