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bad gas mileage, bad MPG, High fuel consumption


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Hello,

I have Cayenne S 2004 and I can get better then 11MPG. They said that is nothing wrong with the car, but I know that this is not normal. I drive it really carefully and on hwy i don't go over 85mph, and I can get better MPG.

I think it's worse in hwy then town driving, which is really strange. But the PCM show me average 16mpg, which is way way off.

Can someone help me with this problem

Thank you

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the MPG gauge is somewhat bad....it can be off from time to time, so i wouldn't count on it 100% of the time.

But back to your question.....11mpg is low, but not that far off....i have CTT, and i know i can go very low, even with a sensitive right foot.

But i might start with your fuel system, maybe you have a leak and that's where the issue shows?

I would suggest maybe the brakes are frozen and causing drag, but the MPG gauge SHOULD show that.....key word SHOULD.

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You might want to check your air filters first because sometime a dirty filter will give you crappy gas mileage. I switched out my air filters and replaced my spark plugs, not only I noticed improved gas mileage but also much better throttle response too.

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Filters,plugs and coils where changed few month ago. So that shouldn't be problem.

I also check it for leaks but there is no leaks.

I know, that consumption can be really bad, but this really can be normal. We are talking about 11mpg with really sensitive foot, If I drive it just a little bit more dynamical, i get 9mpg. So I'm afraid to press it a bit harder.

I was thinking, could be the problem in O2 sensors? But there is no error codes...

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I'm calculating in old fashion way driven kilometers (miles) vs. used liters (gal), I'm not looking at trip computer anymore coz like I said is way way off.

I use 95 octane fuel, and tire pressure is also correct.

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anything engine/emissions related would show in the MPG gauge on the dash. Because there is such a difference between the two, you're looking for something that isn't "engine" related.

So O2 sensors would contribute to bad mileage, but WOULD show on your MPG gauge.

What about tire size? Are you running OEM sized tires? A bigger wheel would show less mileage

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I didn't compare speedometer with gps, but I can check it every day with roadside speed control and it was totally the same, but I can still make test with gps.

Yes the 11mpg is repeating with every fill up. This really make me nervous, coz I have to fill it up every two days and the gas prices here are 8$/gal!

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What gallon are you using? Any long periods of idle? Is the transmission going into high gear and operating correctly?

If there was a sensor problem it should trigger a fault code within two drive cycles. I assume the check engine is working and you've checked for faults.

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I'm using US gallon. There is no long periods of idle, and the transmission is operating correctly.

I'm checking for faults constantly, but there is no faults.

I was thinking if O2 sensor in that years got tired and its not working like then when it was new, but I don't know if that could be possible.

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  • 8 months later...

Our '08 gets maybe 14 mpg around town and maybe 18 mpg on the highway at 75 mph. I guess the ethanol gas is to blame, total suckage!

It is an "S" with bypass pipes, recent plugs and filters, regular maintenance.

Edited by AndyA6
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My '06 CTTS gets around 16mpg with mostly 3/4+ highway and less than 1/4 city. I have done some roadtrips and I know that over 70mph I have to accept that the fuel mileage decreases a fair amount. Other than what you've replaced, as long as your O2 sensors are not throwing a code then I'd say it is a matter of high speed driving. Try keeping it to below 70mph on a tank and see how much it improves but definitely check for any codes first ( by no codes did you mean CEL or did you run Durametric or PIWIS on it?).

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Well, my trip computer also show me average 16mpg, but reality is 11mpg. Truck is running fine, there is no error codes (checked with durametric). Look like that is what it is need and I don't care any more. I like every minute of driving and that counts also.

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You may have a drivability issue that needs to be diagnosed by looking at your fuel trims to determine what area to focus on. I am not going to guess however what you describe could be a fuel regulator/ leaking injectors, vacuum leaks etc. You can have all or anyone of these issues without throwing a CEL. Go see

someone that specializes drivability issues to solve your problem.

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Go do a manual check. filler her up, note the mileage and then on next fill do the math, only way to be sure

I always do manual check. Like I said, 16MPG is counted by trip computer, but if I do math there is around 11MPG or worse all of the time.

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You may have a drivability issue that needs to be diagnosed by looking at your fuel trims to determine what area to focus on. I am not going to guess however what you describe could be a fuel regulator/ leaking injectors, vacuum leaks etc. You can have all or anyone of these issues without throwing a CEL. Go see

someone that specializes drivability issues to solve your problem.

I already did smoke vacuum test and there were no leaks. I really need to find someone who can do more than just look for error codes...

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If the car was smoke tested with out any faults found you only have part of the data. Has anyone looked at the fuel trims or put a fuel pressure gauge on the car? do you have any power loss when you get on the gas? The most important information at this point are the fuel trims.

Edited by binger
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If the car was smoke tested with out any faults found you only have part of the data. Has anyone looked at the fuel trims or put a fuel pressure gauge on the car? do you have any power loss when you get on the gas? The most important information at this point are the fuel trims.

I also make fuel pressure test, and if I remember right, it was 3,8bar, when car was running and and after one hour when car was not running pressure drop to 3,1 bar. I really need to find some expert to look fuel trims. About power loss, I have some hesitation like small vibration, around 1000rpm, if I give him a bit more throttle, but everything above 1500rpm is smooth.

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