Why am I getting bad Gas Mileage?

**JDCMoney** · 06-07-2010

Since I got my GTP in November, I had no 4th gear so I figured thats why I'm only getting 19 miles per gallon.

But a month ago I put a used transmission in. All gears work great engine runs cherry, yet still only getting 19 miles per gallon when babying it and I saw 16ish one tank full when I was heavy footing it for a week.

The DIC is saying a constant 19.3 or 19.4 When I calculate it I have been seeing anywhere from 18.7 to 19.1.

Any ideas?
1998 GTP , 185K, Full tuneup not long ago, with Accel 8.8mm wires, AL104s gapped at .055, Mobile 1 oil and filter. No codes. My interceptor isn't reading any misfiring. It reads less than a degree of Knock under WOT.
My mods are in the signature.

**corsagtp** · 06-07-2010

I have the same question. Best city I get is 18 and best highway is 22. I don't driver hard and I only use 94 octane.

**TorqueAutoMotiv** · 06-07-2010

rich fuel tune would burn fuel faster heavy foot fouled o2 sensor

**corsagtp** · 06-08-2010

Originally Posted by TorqueAutoMotiv

rich fuel tune would burn fuel faster heavy foot fouled o2 sensor

I don't have an o2 sensor. I got rid of my cat and put a o2 emulator in. Not sure if that makes a difference though

**JDCMoney** · 06-08-2010

Anybody else with the DHP tune having bad gas mileage?

My rear o2 sensor is fairly new and is in a spark plug anti-fouler to raise it up due to the cat delete.

**Jakegday** · 06-08-2010

Originally Posted by corsagtp

I don't have an o2 sensor. I got rid of my cat and put a o2 emulator in. Not sure if that makes a difference though

you have a front o2 sensor. those will lose their "touch" over time and starting causing poor fuel mileage, without illuminating the SES

**SnowDrift** · 06-08-2010

The 19 doesn't sound bad around town, really. Was that in the winter?

If I REALLY baby it, I can stay around 22-23 back and forth to work - about 13 miles. On the highway, I've seen 32 mpg and that was a couple weeks ago and always running premium fuel. I've never driven it in the winter, so I don't know what to expect, but I imagine it will drop off a bit.

**dirtmaster88** · 06-10-2010

Originally Posted by JDCMoney

Anybody else with the DHP tune having bad gas mileage?

My rear o2 sensor is fairly new and is in a spark plug anti-fouler to raise it up due to the cat delete.

I've got a DHP tune and have pretty crappy gas milage. Going to have a street tune in the near future