This is for the near-stock Red A4 Z28 in my sig.

Right now my Fiancee is driving the car, short trips, back and forth to work. The car probably is used 4 times a day in 15-minute intervals. My Fiancee drives like a normal, non Z28 owning, person

Anyways, we're getting about 13mpg, and if we take a long trip on the hwy, we might be able to eek out 17-18, but that's it. We're using 91 octane (The best we got here in Cali) and for the most part, the car seems to run fine. The car does seem down on power, but then again, I'm going from the M6/Hotcam/4.10 car to this car.

Keep in mind, the car does have 160k miles on a stock (Never been rebuilt) engine.

I'm thinking it's one of the following:
1. Clogged Cat
2. Bad O2 sensors
3. Dirty Air Filter
4. leaking fuel injectors

Here's a little background on what's been done:
on 11/02 and roughly 144k miles I did a halfway decent tuneup because the car was running horribly:
- replaced spark plugs
- replaced wires
- replaced coil

Then later that month, the car broke the 2-3 transmission shift solenoid, so I replaced that.

In May of this year @ 156k miles, I replaced the TCC switch because the tranny wasn;t locking up in 4th gear (It is now)

In June of this year @ 157k miles, I fried the ECM. I had Madwolf hook me up with a new one, with a HPP3 bin fine added.

I will state that I recently replaced the fuel pump, and I replaced the fuel pressure regulator in 2000.


What I do know is that as far as I have owned the car (Bought in Aug 2000 w/ 120k on the clock) it has not had the following changed:

Fuel Injectors
O2 Sensors
Cat
MAF Sensor
Map Sensor
Knock Sensor
CLT sensor
IAT Sensor
TPS Sensor
and probably a lot more sensors that I cannot think of


Because I know that Lousy gas mileage is directly related in terms of emissions, here's a report from when I smogged the car in April:

15mph:
RPM: 1428
%CO2: 14.3
%O2: 0.4
HC (PPM) (Max/Avg/Measured): 83/21/11
%CO (Max/Avg/Measured): 0.48/0.06/0.03
NO (PPM) (Max/Avg/Measured): 689/150/687

25mph:
RPM: 1903
%CO2: 14.2
%O2: 0.4
HC (PPM) (Max/Avg/Measured): 48/13/11
%CO (Max/Avg/Measured): 0.46/0.05/0.01
NO (PPM) (Max/Avg/Measured): 706/136/613

** Avg is the average passing vehicle's values, they are not the average values of this car. The values for this are are in the last (Measured) column **

I know that NOx production is a product of high combustion temps, I will say this car has the original EGR and (as far as I am aware of) is fully functional.

I plan to get some datamaster logs within the next day or two, however having said all of this, does anybody have any ideas? I'm really scratching my head on this one
Thanks

 

TTT

 

The easiest way to tell what is going on is to get some data when monitored by a scan tool. Otherwise, it is kind of a guessing game.

 

very detailed good job

like shoebox said, scan is better

i would clean out the throttle body, intake w/ deep creep and seafoam too, and run some redline st-1 fuel system cleaner thru there

if scan shows codes, change those things

i recently did O2 sensors and fuel filter

and i just recently cleaned my MAF wires gently w/ plain isopropyl and a Qtip don't press hard at all or you will bend the wires. there was a black coating on all wires, now nice and silver

others recommend electric parts cleaner but i was too lazy to get some. btw my car runs even smoother now, esp at 1000-1500rpm

new cat and catback prob help too

 

If the O2 sensors haven't been replaced in at least 40K miles (maybe more), then they definitely need replaced. I bet that will add a good bit to your MPG and emissions.

 

13mpg is pretty good considering the car has 160k on it. Mine only gets 140 miles to the tank, and alot of that is freeway driving.