First things first, the car itself..

2001 Integra GSR Sedan (DB8)
144k miles
Current avg economy: 10-15mpg (175-200 miles per tank)

Engine runs and idles smoothly, no strange smoke coming from exhaust, engine pulls hard. Does not perform like a car w/ 100k+ miles. feels almost like a new car.

Here's the strange part... Last winter it kept throwing evap codes, p1456/p1457/p1458. That is until around Inspection time in March when I reset the ECU. It threw one last code (P1458) and hasn't had a CEL since.

Now for what's been done.

• 02/11 - Changed cam seals and oil pan gasket.
  
• 04/11 - New Tires
  
• 07/11 - New mid-pipe installed, new NGK Iridium plug and NGK wires put in.
  
• 09/11 - Seafoam treatment.
  
• 11/11 - New pads and rotors.
  
• 12/11 - Hooked up to a Snap-On engine diagnostic monitor, everything showed to be within spec.

Soon to come:

• New cap and rotor
  
• IACV cleaning
  
• Valve adjustment (maybe)
  
• Alignment
  
• New calipers all round + e-brake cable replacement

Now for some questions.

How much can a dirty IACV effect gas mileage?

Anything else I might be forgetting?

 

Usually bad gas milage would be the o2 sensor, or a heavy foot lol.

 

o2 sensor fine. Heavy foot? not so much, I rarely rev above 3k. Can't afford to have much of a heavy foot where I live, the roads are too messed up.

 

Well if it was throwing codes and all you did was reset the ECU then there may still be a problem with the system...

 

Yeah I've considered that except for the fact that it hasn't thrown a code in 9 months. I've checked the systems that correspond with the codes and so far everything checks out though every once in a while I do smell gas fumes in the engine compartment after starting my car from a cold start.

 

Try fuel filter.

 

Rarely does a fuel filter cause much if any problems. Especially that poor of milage. Hopefully you took down the codes before you reset the ecu. I'm gonna have to say that those were your problem, considering all of them being EVAP related.

 

^
a neglected fuel filter can be the root of a lot of problems...spend 20 bucks and change it out if you havent done so..


is your temp sensor reading correctly? if it reads cold all the time, your car will run richer.

 

Only if the filter is like completely clogged, which hardly ever happens. I have worked at several shops, and never seen a fuel filter be the root of any of the problems. It is very unlikely that a fuel filter goes bad or gets clogged.

 

If you smell gas fumes sometimes, and you had an issue with the Evap system in the past that was never resolved, and you get unusually poor mileage... I would guess the car is leaking gas, or gas fumes from the evap system. But the system just isn't catching it for some reason. Look for leaks in the entire fuel and evap system, from the fuel tank forward.

 

my civic with a gsr swap did this, then i bought an new air intake and it stopped.

 

i would say air filter check/clean/replace whatever.......fuel filter to be safe......tire pressure.....my teg ate up half tank in two days.......i replaced one of my tires last week and just checked pressure and on was at 20 psi..........filled all tires to 35 psi and all is good now.........cap n rotor next on my list to do.........

 

What exactly is the o2 sensor reading?

 

That right there will hurt mileage in a GSR.

Drive it like it wants to be driven, and the mileage will increase.

Also, the vast majority of drivers have absolutely no clue how to coast down to save fuel (and brake pads). Something to think about while driving at least.

I used to average 16-18MPG in my 00 GSR. Rev it up higher before shifting, leave it in a lower gear to keep the engine in a more efficient RPM range, learn how to coast down better, and the same commute was 22-24MPG.

 

What's the best RPM for best efficiency (w/GSR gearing)?

I'd jack it up for get it where you can spin each wheel to be certain you don't have a bearing failing, caliper sticking, etc.. should spin freely. That can drag you down without being noticeable.

Mark

 

^^ I agree. The lower the RPM the more pedal needed to maintain it as apposed to downshifting and being light on the throttle and staying at 4.5k.

 

The gearing is irrelevant for RPM efficiency, other than the fact that Honda already did the homework and gave you a car with the correct gearing.

Close enough.

4.5k is a little on the high side for the lower gearing, but really isn't a bad point for the load needed to go that fast in 5th gear.

My mileage improved significantly keeping the car above 3k around town. Use moderate throttle for accelerating, allow the car to rev slightly higher in each gear as speed increases, don't force the last shift once you get to cruising speed if it will drop the car below 2.8k (give or take).