cjones42

Hi Guys,
My truck always would get 18-20 mpg no matter what I was doing but over the last year I can not get over 16 mpg. Its not fuel so let get past that one. This is what I know:

I have good rail psi
Pusher pump is at about 25 psi
Smarty at SW7,tq3,RP2,timing 3(Multiple prgs)
Tried driving truck stock
Speedo is right on confirmed my GPS,Tachometer and radar gun.
Tranny is definitely not slipping
Changed all filters on a regular basis

Any input would be great. Thanks Guys!

cjones42

If I don't have a enough turbo or its bad can a turbo cause bad MPG?

jhenson

Very doubtful your turbo is the problem. Have you always used the same filling station? I know around my area, certain stations I JUST DON'T USE!!! I have found that one Shell station in particular always nets me the most gains on my mileage. Also, are you hand-calculating your mileage or going by the overhead?

Also, as fun as certain programmers can be to drive with , are you using a light foot on the go fast pedal?

Spooler

Injectors or loose cross-over tubes.

cjones42

I have tried multiple station hrs apart from each other. I know its not fuel.
I hand calculate mileage all the time since I ordered it in 2003. That's how I know something is wrong. I haven't changed my driving style so I doubt its the Smarty. Since I drove with it stock for a couple of tanks with no change. Everyone I know that is using Smarty gained mileage. Its something but I don't know what.

kully560

well this is what happened to me 2 years I put a donaldson muffler on part # 85171 with close to 3000 rated flow @ 2 hg . did not like the loud sound and my milage droped to 18.5 hwy.everbody says no back pressure is better, I do not know? so I called donaldson tech line to get a part # same size 44 " long but not as loud. they told me to use 85421 which has less flow rated @ 1720 but was closer to my output of 1563.all I can tell you is now I get a little over 20 mpg hwy allways hand cal. and truck is some much quieter than before. no difference in performance .

Shorts

Won't efficiency drop over time from simple mechanical wear?

Another thought is have you gradually added more weight to the truck by way of tools or accessories and general 'stuff you carry'?


I'm thinking is a very broad scale here.

thor1721

sounds stupid but how bout tire pressure. or different tire size or tread pattern for that matter. just a thought

John_P

I agree with what DTR Member Spooler has told you on the CR injectors being the possible problem. At 100,000 miles, my 2006 began having long crank times along with lower mileage and occasional white smoke. The problem with my truck WAS the injectors. I had low pressures on two of them and a solenoid problem on another one. Your diagnostics showing good fuel and rail pressure may not neccasarily show what is really going on with the injectors.
If you haven't changed them, I would pull them and at least have them checked. It is a pretty easy job to do. IMHO,.....these CR injectors are not very reliable!

lane22

could be draging calpers or hub bearing going out

Gatorama

Dirty MAP and/or MAF sensor could be the culprit. CRC makes a MAF cleaner that works pretty good. Regular ritual on my undeleted 6.7.

Rednax

I always hate to think about the injectors.

Otherwise:

R&R filters
Brake drag (hot or cold)
Steering wander
CAC leaks
Alignment
Tire pressure

MPG is sensitive to small factors. Any of these can be "off" only a little. But added together can account for mpg drop that's noticeable.

And congrats on using mpg to track problems. Even a 10% is cause for me to pay attention.

Has your driving changed? Extended idling? Different commute? (Any changes to average mph?)

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