Tell us what worked for you.

 

You can easily test o2 sensors.

1)Remove from car.
2)Put 12 volts to the heater (2 same colored wires) and it will heat up in a couple minutes, if not replace
3)find the pin with continuity to the case. Attach volt meter ground to this pin or case.
4)the remaining wire is the 0-1v sensor output

5)in air, the sensor will read zero or slightly negative voltage. Using a butane lighter, displace the atmosphere inside the cage with fuel (no flame) and the voltage should rise to over 500mV, if not replace.


Sensor should have immediate reaction time. With butane in the cage, you will need to blow into it to remove the butane too see a quick voltage fall time.

I've tested several like this recently and Ive noticed the ones that have failed see a decrease in voltage (go negative) when oxygen is displaced (opposite of a good sensor).

 

Never put two and two together. My driver's side JBA shorty has been leaking from #3 since they were installed in 2003 but never thought an exhaust leak at the header flange would lead to bad gas mileage. I put no more than 500 miles max on the car over the summer so I just figured I had a heavy foot. This thread explains why I only get 10 mpg at best.

Can the exhaust leak lead to future problems or just bad gas mileage, O2 sensors are original? Motor runs great and consistently puts down 360 rwhp.

For those that remember my MAF Pink wire hasn't been an issue since replacing the Pigtail last summer

 

You should be getting better than 20 MPG on the highway. Hell, I get that from my car at 70 and I'm running 4.10 gears in an A4!

 

I get about 24 when i drive 80

 

The shop which performed my mods 2 years ago also told me that the stock fuel pump was starving the engine while on the dyno. They suggested a new Walpro, which would of course require dropping the rear & exhaust so I haven't done anything, no $ at the time. Maybe this summer I'll have them do the swap. I'd do it myself but no lift in my garage.

Could an overworked fuel pump also cause bad mpg?

 

I doubt it. I would think you would be starving for fuel at some point if your pump was going south. That doesnt' have the same effect as a header leak.

 

Cutting a hole in the trunk to access the fuel pump is such a better way of going about this... I can pull my pump in 5 minutes.

 

Yes, I know but SLP only made 106 LT4's in '97 so I'd hate to cut sheetmetal. Thanks for the suggestion.

 

lol, well I averaged 20 mpg two tanks in a row, then the next it went back to 14, then yesterday at 15.

next weekend I plan on fixing or atleast locating the exhaust leak, somewhere on passenger side. Im going to also try seafoaming it and check the 02 sensors.

 

I'd test the 02's first. If one fails it will default to open loop and noticably increase fuel consumption.

or maybe someone was joyriding it