My 89 Si Hatch with a D16y8 swap and bolt ons went from a steady 350 miles on a tank to all of a sudden 200/225 miles on a full tank.

WTF

Nothing changed except for a Dyno Tune on a Apexi AFC....and all the adjustments on the tune were to LEAN out the motor. So fuel economy should have gotten better, not worse.

I am so damn confused.

Ideas?

 

don't know if this applies to your situation, but i run thick motor oil and when the temps drop the 50W contributes to lesser fuel economy.

 

I'm running 10w-30 have been all season.

Does that matter?

Another question.

The injector resistor box has nothing to do with this correct? If the box is either...Working....or NOT working. There is no inbetween? or am I wrong in this matter?

 

well every morning I warm up my car for a good 10 mins and I see about a 50-75 mpg decrease per tank......have you been warming up your car lately?

 

Your foot turned into lead...

 

No, I dont warm up, but now that you metion this.

My car has been not able to idle at all when I first start it, untill it is up to temp. It just falls to like 200 RPM then dies out.

 

Maybe check fuel pressure?

 

check T-STAT check for proper opp! but if your running lean the ecu trys to correct.

 

My mileage always dropped like a stone when it got cold - like below 32 - outside. I think the fuel has a harder time vaporizing at the lower temps, so it's not running as efficiently.

 

o2 sensor?

I was running about low-mid 200s before i changed out my o2.

 

O2 sensor. Check to see if you have any codes.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by groundedcivic91 &raquo;</TD></TR><TR><TD CLASS="quote">No, I dont warm up, but now that you metion this.

My car has been not able to idle at all when I first start it, untill it is up to temp. It just falls to like 200 RPM then dies out.

</TD></TR></TABLE>

Bad CTS, maybe?

 

check for vaccum leaks my buddy had a bad one on his car and was only getting like 150 miles to a tank.

 

write down all of your afc settings and put it back to 0 and see if your mileage improves.

 

i changed my fuel filter, sprak plugs and my o2 then i get abt 360 miles a full tank

 

check your fuel filter to see if there's any leakage or cracks, also check your fuel line that goes into the fuel regulator if u have one, if not check the fuel vaccum hose that's connected near the brake booster hose. Could be a leakage.!!