tundraphile

We have had our 2004 Cayenne Turbo for a couple of months and about 3000 miles.

Lately it seems the fuel mileage has been getting progressively worse, and when started from cold you get a distinct whiff of raw gasoline. The exhaust smells like an old muscle car running very rich. Initially with cruise on the interstate it would seems to avergae 18+ mpg @ 75 mph. Now it seems that is more like 16 or 17.

I am ordering a Durametric cable this week since it is time to service the car, but does anyone have any ideas on common reasons for this with the Cayenne?

ltc

fouled plugs would be a place to start....perhaps the coils were replaced and the plugs were not...

Cole

If it is running rich it should throw a code and trip the check engine light.


How many miles on it? Cats clog overtime. When they do it will effect gas. Mileage and sometimes have a smell associated with it. The service life of a cat is supposed to be about 80k miles. Many run them further than that, usually until they have clogged so bad that the car barely runs. The life can vary depending on how you drive, fuel quality etc.

tundraphile

I should have included more information. Car has 50k miles. No CEL or other warnings. I don't know if the coils have been replaced.

The engine doesn't seem to be rough at idle or anything, but it is difficult to say as the car is new to me exactly what is normal.

My first thought was perhaps an injector "stuck open" if that is possible, but I would assume after 250 miles or so it would have fouled the plug and I would have a CEL. I'm not sure how a faulty O2 sensor would affect this, whether it would run rich or lean if the sensor was faulty.

After doing a little more research I read that sometimes a gasoline smell can result from a leaking fuel filter. No evidence of fuel dripping under the car nor a smell in the cabin. The mpg I mentioned was from the dash display, so I would assume that is unaffected if fuel is leaking rather than being injected. I'm tempted to change that (along with air filters) as a matter of course, I don't know the exact service history of the vehicle. The plugs probably should be on that list as well.

Perhaps the diagnostic cable will give errors. Or perhaps drive it a bit more until I do get a CEL, at least then I would have a direction to look.

Any other suggestions would be appreciated.

leek

Mine has always run rich for the first few minutes (a little louder too) after several minutes it leans out and quiets down. The milage at 75 looks about right. I average 14.1 with probably 70% freeway or highway driving. It will do better if I stay out of it but that is tough to do.

airdiesel

The mpg display in the instrument cluster has beening showing 13.1~13.3 for the last few years. It reaches high 13 after 100% freeway driving over 200 miles. But, it persistently goes back to 13.3 after some mixed driving as if it is a default display.

CDH-CTT

tundraphile,

You might have a MASS air flow sensor going out... I know my CTT did the samething... MPG was slowly getting less and it "felt" slower and rougher... I replaced BOTH my MASS air flow sensors with new ( takes the same MASS meters as a VW VR6 engine just need 2 of them) and then I had POWER again!!!!!
Good luck

Carl

tundraphile

OK, so another odd symptom today. Car had used 91 octane on its previous tank. Filled up with 20+ gallons of 93 octane tonight from busy station (never had a problem with fuel before there). Upon restart, the engine is subtly stumbling and idle is lower than before. No stalling or hesitation. I will drive it tomorrow 120 miles or so and see what, if anything, changes.

Could the octane sensor be another potential cause?

Andy E.

This could be a long shot but have you checked your air filter?

As stupid as it may sound, the symptoms you're describing sounds like an air restriction of some sort which usually points to an extremely dirty air filter element. That or as CDH-CTT mentioned, a defective MAF.

ltc

fuel pump

CDH-CTT

or fuel pressure reg .... should be able to test fuel pressure at the front sides of both fuel rails...

touareg

Wow, what am I doing wrong? I have 7 minutes of back roads and 18 minutes of highway and I get ~17 going 85MPH all the way on the highway. If I throttle it back to 60MPH or so I get to 19. Only time I get 13 is if I get stuck in stop and go for 35 or so minutes.

Cayenne S and yes I checked for the 2 extra cylinders Mine is an 05 with 88K on it. I don't have a turbo like you though.

airdiesel

Mine is 04 turbo. Over last weekend, the display was showing 12.8 after some city driving. Maybe, it is time for me to check MAF sensor as well.

Kermit

On my 04 turbo I get about 15.5-16 mpg with "ordinary driving" (not that fast, smaller roads, car full of crap). When on a freeway and driving like a nut, or driving in heavy traffic, it's closer to 12

Though when I changed my plugs a few weeks ago they all looked very dark, think it's running a bit rich too. I'll start with replacing my air filters as they haven't been changed in a long time and might be a bit clogged. Maybe the air mass sensors after that if it doesn't help.

tundraphile

Has anyone had any luck cleaning thier MAF sensors with a product made by CRC? Reviews are generally positive of the results even if short-lived.