Confused about gas mileage

[Puckpimp71]

Not complaining here, but when I first got my car, I averaged about 25 MPGs... After modding it lightly (intake, midpipe, 10psi max on dual stage controller) my mileage got slightly better. Now, in the past year or so, after installing DSM's AFC I was getting about 22-23 MPG on 10psi, 20 on 7psi.... I noticed the decline from 25mpg mainly after taking my car to the dyno. After installing the SMIC and intake maifold, there was little change in my mileage. When I put MAM's exhaust manifold in, it didn't have a big effect in my mileage. A few weeks ago after 3 or 4 tanks of gas, I was getting as low as 17 mpg.... So here's where I'm lost, the last three tanks of gas got me an average of 26mpg. Driving habits and gas choices haven't changed much. What gives??? Anyone else have this happen?

 

[Dugg E Fresh]

Maybe better quality? I know mine can vary even getting gas at the same place. Mine does range some (not near as much as 9-10 mpg) from 28 on up to 32/34 without really changing driving habits.
Maybe just another "quirk" of this car?

 

[BradC]

Plugs, dirty air filter, different tires, tire pressue? etc, etc

 

[Puckpimp71]

same plugs, tire pressure, etc... Even from the same gas station.

 

[8cd03gro]

did you get it tuned at the dyno? If so, the tune is probably running richer than you were before to compensate for the extra boost, thus burning more fuel.

 

[mryellermp5]

Ecu

ECU recalibrating maybe? weather? other than gas flucuation(sp) just my .02.

 

[MrDiggler]

Not to scare you, but years ago I noticed my gas mileage dropping on my first 323 GTX. It crept down to just under 20 mpg before my mechanic noticed that I had almost totally lost compression in the #4 cylinder. Between it happening steadily and the turbo compensating, I didn't even realize it occurred.

If only just to rule that out, I'd do a compression check. If you see any anomalies, I'd get a full leak-down done.

 

[Puckpimp71]

Yah... That's what I was thinking, surprised about how it crept back up though. :-( hopefully it isn't the case

 

[MrDiggler]

Ahh, I didn't catch that it came back up. Weirdness.

 

[Moonman8]

I don't mean to threadjack and my question is slightly on topic:

How intensive is a compression check? I've never had one done on the very few cars I've owned. I know a few Mazda techs that have access to the equipment but I'm curious about how much work it would be for them and how much I should offer to pay them for it.

 

[Dugg E Fresh]

I don't mean to threadjack and my question is slightly on topic:

How intensive is a compression check? I've never had one done on the very few cars I've owned. I know a few Mazda techs that have access to the equipment but I'm curious about how much work it would be for them and how much I should offer to pay them for it.

I borrowed a tester from a friend of mine and looked up (either on this forum somewhere or someplace else online) to find out how to do it. I checked mine and was relieved to see a steady 183-185 across all four. It's really pretty easy. All you do is pull the plug, one off the coil pack (i believe), put your tester in, crank, and read the pressure gauge. Then proceed one at a time.

 

[Moonman8]

I borrowed a tester from a friend of mine and looked up (either on this forum somewhere or someplace else online) to find out how to do it. I checked mine and was relieved to see a steady 183-185 across all four. It's really pretty easy. All you do is pull the plug, one off the coil pack (i believe), put your tester in, crank, and read the pressure gauge. Then proceed one at a time.

thanks for that quick and dirty how-to. Since we have the equipment at work, I could probably get my hands on it to do it myself.

[/threadjack]

 

[MrDiggler]

It's very easy.