2nd Gen Non-Engine/Transmission MPG and tires

[drrhoades]

I just put on a set of LT265/75-16D BFG All Terrains and I noticed that my mileage has dropped between 2 and 3 mpg. The truck came with a set of Cooper Discover ATs that were 265/75-16C. Would the tire stiffness and slightly more tread affect the milage that much? I was wondering if my timing had slipped and if it would cause that big of a change. The power still feels the same but sometimes I think that it is a little lower then usual. I am able to make 24 lbs of boost. Also the truck is completely stock as far as I know. It has 75,000 miles on it now I have put on 7,000. I took a 1,500 trip at the beginning of July and got over 21 mpgs every fillup and that was calculated without the correction factor of 3% for the bigger tires. This trip was with the old tires.



Thanks,

Doug

 

[Mundgyver]

Seems like a lot of drop there. What size tire did it originally have in stock oem form. I guess the next question would be what do the egts look like. Have they taken a jump up lately which would indicate the engine to be working harder and the last thing would be when was the last time you used and injector cleaner and do you use it on a regular basis.

 

[drrhoades]

The tire size orignally stock from the factory was 245/75-16 and the tires that I had on it before the BFGs were 265/75-16 which are the same size as the BFGs. I was just saying that the speedo is not reclaibrated for the larger size tire and that I have never used the recalcuated number to get a correct mpg reading it had always been above 20mpg. As for the EGT gauge I do not have it hooked up yet as I just got gauges, I only have the boost done so far. At 70 mph I am running between 5 and 6 lbs. I have only used injector cleaner once (in June) and it didnt make a difference in the mpg I was consistently getting 20 mpg or better before I used it. No I do not use it on a regular basis.



Doug

 

[Mundgyver]

The only other thing that you might try is pulling the engine manifold temp sensor and the manifold pressure sensor located tor wards the back of the manifold on my truck (not sure about yours) and just clean then using break cleaner with an alcohol flush. I did this at 90,000 and picked up about . 2 mpg. I run an exhaust brake which can cause a carbon build up on these two sensors.



How are your brakes. Don't have one dragging. Probably not.



I'm out of ideas. I run the injector cleaner once a month. I use 32 ounces at once which is suppose to do 100 gallons, but its just easier that way. When I put in my 275 injectors at around 20,000 the old factory stock ones look brand new with no carbon on them at all, doing this method.

 

[drrhoades]

Thanks Mundgyver I will try the injector cleaner and see what happens. I guess it can't hurt to try.



Doug

 

[Mundgyver]

I have had very good luck using the Power Service and have never found any water or dirt in the filter when I do the servicing. Fuel filter I forgot !!!! Check your fuel filter before your toss in the Power service. Change it out and then pop in the Power Service.

 

[ox1]

As far as the tires go, are the new ones inflated to rec specs? I have already got E tires put on my truck and come to find out the moron put 32# air in them! I run the very same tire on the wifies 'Burban and only run 50 or so pounds, but 32? Idiot!



A yr or so ago when the gas prices went up like they are now for the first time, Fourwheeler magazine did an articall about better milage. They did both airing up the tires to spec and driving speed limit. Both produced gains. Speed being the major player, but I was very surprised at what numbers they got just from airing up the tires! When it was all said and done, they gained 40-50% better milage! :--)



Yeah, check the filter.

 

[Howard Durand]

During the time I had the 245/16 tires on my truck, actual miles driven were always 2% less than the odometer showed which would indicate a better miles per gallon than I was really getting.

When I changed to the 265/16's the measured miles were 2% more that the odometer which looks like a drop in MPG.

That is a 4% difference between the two sizes which would account for some of your loss.

 

[drrhoades]

I will look at the fuel filter. I wish I had a duel fuel pressure gauge that way I could tell if it was dirty or not. Also I realized that I have been doing alot more city driving then I was before so that might be the reason as well. As for the 245/75-16 tires I have never had them on the truck it had 265/75-16 on them. Yes the air pressure is up to spec I am running 55 and 45 front and rear.



Doug