Gas Milage drastically decreased

reesea17 · 02-12-2012, 10:15 AM

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 · 02-13-2012, 05:51 AM

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 · 02-13-2012, 10:48 AM

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

Sigiwald · 04-25-2012, 05:43 AM

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

COMPUTEK::WMS · 04-26-2012, 06:26 AM

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) · 04-27-2012, 01:06 AM

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

reesea17 · 04-30-2012, 06:51 AM

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 · 04-30-2012, 06:52 AM

Quote:

Originally Posted by 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.

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

papuc (MMI S4) · 05-07-2012, 02:09 PM

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

S4incter · 05-14-2012, 05:01 PM

Quote:

Originally Posted by Sigiwald

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

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....

04-26-2012, 06:26 AM	#5
COMPUTEK::WMS AudiWorld Senior Member 2001 Audi S4 Join Date: Apr 2005 Posts: 689	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. __________________ Engine-AWE Full Stage 3 Kit w/o manifolds,GIAC X and XR M Box 5 prog. w/flashloader,IC w/shrouds,DP w/test pipes,RS4 Eng. Mnts.,RS4 Tran. Mnts.,Millitek 3" Catback Exh.,Evo Intake,APR Snub Mnt.,Forged Diverter Valves,Samco Sport Blue Silcon Hose Kit Driveline-CM Stage 4 Clutch,CM LW Flywheel,Stasis Center Diff. Brakes-Alcon/Stasis 6 POT Calipers, 14" 2 Piece Rotors,Stasis Rear Brake Upgrade,Goodridge Stainless Steel Brakelines Suspension-Bilstein PSS9 Coilovers,Nuespeed 19mm Rear Sway Bar,AWE DTS Accessories-19" Neuspeed RS10 Silver Forged Rims,AWE Vent Boost Gauge,AWE Pedals,Alcantara Shift Boot,Valentine 1 Hardwired,Pioneer AVIC-D3 w/bluetooth and iPod connector,Alcantara Interior,Clear Corner Mod,RS4 Bumper,CF Hood (Painted),M3 Lip,RS4 Grill

04-27-2012, 01:06 AM	#6
papuc (MMI S4) AudiWorld Senior Member Garage is empty, add now Join Date: Nov 2007 Posts: 853	I would look at the 02s first, unless you're getting a code for EGTs. __________________ 2001 Audi S4 6MT GIAC-X Bosch 710n Bilstein Shocks w/ H&R Springs AWE Vent Gauge V1 Hardwired w/ ToyGuy concealed display Greddy Turbo Timer Stage 1 Custom 3" Milltek exhaust on the work bench. Piggies, whenever I get to it. Maintenance needed: Timing Belt. In 2K miles and counting. Oxygen Sensors.

05-07-2012, 02:09 PM	#9
papuc (MMI S4) AudiWorld Senior Member Garage is empty, add now Join Date: Nov 2007 Posts: 853	EGTs won't necessarily throw a code. Best bet would be to scan it using Vag-Com. __________________ 2001 Audi S4 6MT GIAC-X Bosch 710n Bilstein Shocks w/ H&R Springs AWE Vent Gauge V1 Hardwired w/ ToyGuy concealed display Greddy Turbo Timer Stage 1 Custom 3" Milltek exhaust on the work bench. Piggies, whenever I get to it. Maintenance needed: Timing Belt. In 2K miles and counting. Oxygen Sensors.

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02-13-2012, 05:51 AM	#2
thejulex AudiWorld Senior Member Garage is empty, add now Join Date: Aug 2009 Posts: 855	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.

02-13-2012, 10:48 AM	#3
akop18 Audiworld Junior Member 2000 Audi S4 Join Date: Jul 2009 Posts: 18	Sounds similar to my buddys B5, his EGT sensors failed like thejulex said, I would start there.

04-25-2012, 05:43 AM	#4
Sigiwald AudiWorld Newcomer Garage is empty, add now Join Date: Apr 2012 Posts: 6	I have bad EGT's and I still see 20-22 mpg. Could be your O2's

04-30-2012, 06:51 AM	#7
reesea17 Audiworld Junior Member 2001 Audi S4 Join Date: Jul 2011 Location: Lubbock, TX Posts: 19	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?

05-14-2012, 05:01 PM
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