reesea17

Within the last two months I have seen a drastic decrease in my fuel economy. I figured it may be caused by a bad purge valve as I got an engine light a while ago pointing towards emissions/purge. I recently replaced the purge valve after a long time trying to find the little sucker, and don't see much improvement in the milage. In between the time I had to have the tranny and clutch swapped out and that hadn't done anything to hurt or fix the problem.

I realize this is all very vague in detail but I was wondering if I might be able to get a couple of y'alls input on what possibilities I might be able to try out in order to fix the problem. I went from getting about 19-20 mpg city to 12-13 mpg city. I need to fix this problem as it is currently nearly costing $50 to fill up the tank each time. Thanks in advance.

thejulex

There are usually several culprits:
1) your EGT sensors failed (common on 2.7t) and engine is dumping fuel all the time
2) your O2 sensors are on their way out, causing you to run rich
3) your MAF failed and is giving wrong readouts

Usually it is #1, sometimes #2, rarely #3 unless you have bosch maf which is known to fail frequently.

akop18

Sounds similar to my buddys B5, his EGT sensors failed like thejulex said, I would start there.

Sigiwald

I have bad EGT's and I still see 20-22 mpg. Could be your O2's

COMPUTEK::WMS

Are you stock or Stage 3?

I am currently stage 3 with I believe the green top injectors and I have pretty much always got 12-13 MPG in the city and 18-19 MPG Highway for years even with getting new EGT and O2 sensors.

papuc (MMI S4)

I would look at the 02s first, unless you're getting a code for EGTs.

reesea17

My question here is whether failing EGT sensors would give me a check engine light? Or would I only be able to read it using a VAGCOM?

reesea17

My S4 is stock except for a Vented Air Box (Darintake) and a recent transmission replacement.

papuc (MMI S4)

EGTs won't necessarily throw a code. Best bet would be to scan it using Vag-Com.

S4incter

Agree, EGT is just a safety margin. Too hot of EGT will cut timing... I don't even run them and they are tuned out. If O2 sensors are getting lazy, could do it. But I would check your coolant temp sensor. That would tend to dump more fuel than any of the above....