Using AC = MPG halved???

O2ShootTheJ · Jul 21, 2011

Okay I've had this issue for a while now, and maybe its just the nature of the beast, but I'm hoping I have something wrong. When I turn my AC on no exaggeration I use about twice the fuel as I usually do on trips. Is everyone elses truck like this or do I have something wrong?

Getting tired of driving with the windows down in 100+ weather

littleredstroker · Jul 21, 2011

ill lose 2 or 3 mpg but never in half...

Spatel23 · Jul 22, 2011

have you hand calculated this difference?

JAP · Jul 22, 2011

There. I fixed it. Next question!

DcMoore · Jul 22, 2011

Dtm030 · Jul 22, 2011

Could the air unit be seizing up and put way more pressure on the belt?

That could be dumb but I had to ask. The unit on my 2008 was making squeeling noises on start up all the time, sounded like it may have been going out but never did.

Dzchey21 · Jul 22, 2011

yeah half doesnt seam right, and even then 1 mpg is probably a stretch to be honest.

Driving the supercharger, which i know takes more HP then an a/c compressor mileage didnt change much if any, so i dunno, sounds like you may have a bigger issue but who knows.

TurboM700 · Jul 22, 2011

Not saying this is the case here but the mid 2000 year Ford tauras had the same issue and it end up being whent he AC was one it would change the 5v ref to the MAF sensor causing it to think it had more air going thru it and this would cause a rich condition along many other things. Its been a while since I have worked on a 6.4 so I cant say if they even have MAF sensors. I know the 6.0l do and thats mostly what I work on.

It was an easy check with the vehicle running and up to temp. Read the MAF value on the scan tool and see if it changes with the AC on or off. Do this both idleing and going down the road.

Mike

UPINSMOKE · Jul 22, 2011

What mpg are you getting with the a/c on? What speeds are you rolling at?

O2ShootTheJ · Jul 22, 2011

I haven't done a legit MPG calculation w/ AC on and off but I'll go ahead and try to do that. I guess I'll fill up, turn the ac on, drive somewhere, and fill up again for the AC test.

I've just noticed that a drive of about 30-35 miles or so will usually end up using about 1/8th a tank there and back with the ac off and closer to 1/4 tank there and back with the ac on.

TurboM700 said:
Not saying this is the case here but the mid 2000 year Ford tauras had the same issue and it end up being whent he AC was one it would change the 5v ref to the MAF sensor causing it to think it had more air going thru it and this would cause a rich condition along many other things. Its been a while since I have worked on a 6.4 so I cant say if they even have MAF sensors. I know the 6.0l do and thats mostly what I work on.

It was an easy check with the vehicle running and up to temp. Read the MAF value on the scan tool and see if it changes with the AC on or off. Do this both idleing and going down the road.

Mike

Thanks Mike I will definitely check this out.

Dzchey21 · Jul 22, 2011

you can check mass air flow with a dashdaq if i remember right

O2ShootTheJ · Jul 22, 2011

yea i checked it on the way home. maxes out while im driving but at idle it didnt vary at all between ac being on/off.

I'll see if i can get some solid mpg numbers over the weekend

Dzchey21 · Jul 23, 2011

Does the fan run more with the a/c on?

BFT · Jul 23, 2011

city or highway driving?

eric.davis · Jul 23, 2011

I know this is probably isn't it but do you have a fuel leak anywhere.

O2ShootTheJ · Jul 23, 2011

Dzchey21 said:
Does the fan run more with the a/c on?

Yea I'm pretty sure it does.

BFT said:
city or highway driving?

Mixed

eric.davis said:
I know this is probably isn't it but do you have a fuel leak anywhere.

I used to, but I would hope that problem was fixed back in April

BFT · Jul 24, 2011

i see a big time loss with city driving with the A/C on. i normally leave the A/C off until i hit a long stretch of highway and a consistant speed

jdgleason · Jul 24, 2011

Maybe the clutch is going bad

GROSSpolluter · Jul 25, 2011

i dont notice any milage difference with the a/c on or off. its a diesel not a nissan sentra.

BFT · Jul 25, 2011

you probably wont notice the small loss if you do small commutes. to people that drive far and tack on 3-5k in less then a week it makes a difference. noticing how many you mailes you get to a tank, lets say the op gets about 400-450 miles to a tank and now gets about 300-350 is big