Gas milage

[navdoc101]

I've had my 'stiva almost a year now & the gas milage sux as far as I'm conserned! Only getting around 26 - 27 mph. Everything was replaced by the po ( a Mechanic) before I bought it. Belts, wires , plugs, Dizzy cap & rotor. I changed the fuel filter & seafoamed it right after I got it. Its got 175/70- 13s now but the mileage never changed ,for better or worse. It runs great & I do get on it a bit. Hehe! I drive mostly city, with some hwy. Best month i got a little over 29 mpg. Any guesses why the lousy milage? Thanks all.

[Flyin4stroke]

Have you checked the timing?

[Pu241]

Not unexpected for an ATX, but sucks for a 4/5 spd.
Which do you have?
Maybe add that to your signature.

[Tommy]

I have an auto in mine and I got down to 24.6 mpg I tried everything and it turned out to be where the intake tube went to the carb or throttle body (mine is fuel injected) it had a small gap in it one that you REALLY have to be looking to see, I pushed it back on there and tightened the clamp and instant 33mpg. Anyway the point is look to see if its sucking air anywhere.

[navdoc101]

Timein' correct, & its a 5 spd. with A/C thats on all the time.

[walth]

oh wow...my number one trick is if you need to speed up, turn off the a/c until you get close to speed, then throw it back on and you've reduced the load on the engine by quite a bit. Hope that helps you.

guess you could check with some carb cleaner sprayed around the intake for a leak like Tommy had too. never know...

and in trying to improve, how soft have you been able to get on the car...like 1500-2000 rpm shifts religiously, etc? It sucks but...necessary.

[sc72]

I had some problems with gas milage and with the help of Festyboy he mentioned i should maybe change the o2 sensor and replace with the Denzo brand, now the car gets around 38 on average.

[Click_It]

I'm having similar issues though not quite as bad as you (see my sig)

I've done all the little things, ie: spark plugs, leads, air filter, fuel filter, carb/injector cleaner, engine conditioner.... All made no difference. I've just switched from 20W-50 to 10W-30 (API "SL" not SM) which some here on FF have said can make 2-3mpg difference. I only did this tonight so I can't comment on results just yet but the basic theory suggests I should see some improvements (engine can turn thinner oil easier = better mpg)

Others here have reported good results from replacing the o2 sensor and cleaning the EGR valve out which I'm going to do next however it looks like your injected so you won't have an EGR. Your o2 sensor could be bad. $20-40 for a replacement but the job itself doesn't sound fun.

The other thing to consider is not just how you drive but where you drive? ie: I do 80-90% city driving and I live in a hilly area so I'm kind of doomed geographically. If I can get to 33-35mpg from my carbed B3 I'll be thrilled. I see you drive 66% city so unless you're going up and down mountains all day I'd expect you should be around the 33-35 mark already. I'm really thinking o2 sensor now. But also tell us what oil you're running. Easy gains if you're running bad on both of these.

Keep us posted, I'm particularly interested.

EDIT: Pipped by seconds, see post above also mentioning o2 sensor. And DENSO is the brand to get not BOSCH. Both will work but DENSO will deliver the best economy (Festyboy explains the technicalities on a thread somewhere) but all you need to know is DENSO is the more efficient of the two and definitely worth getting if you go down this route.

[Pu241]

Check out the temp sensor on the intake manifold.
Many members have had issues with performance/MPG because the sensor was bad and the giving incorrect data for the ECU to run the engine.
Green connector underside of intake manifold.

[ericsmith32]

I've had my 'stiva almost a year now & the gas milage sux as far as I'm conserned! Only getting around 26 - 27 mph. Everything was replaced by the po ( a Mechanic) before I bought it. Belts, wires , plugs, Dizzy cap & rotor. I changed the fuel filter & seafoamed it right after I got it. Its got 175/70- 13s now but the mileage never changed ,for better or worse. It runs great & I do get on it a bit. Hehe! I drive mostly city, with some hwy. Best month i got a little over 29 mpg. Any guesses why the lousy milage? Thanks all.

Are you figuring in the offset for the bigger tires? Use miata.net's tire calc to get an average. Won't be exact but close enough. The o2 sensor is a big one already suggested by Karl. Also watch that right pedal it hurts more than you'd think. On mine I was getting around 32mpg then I changed my disty since the old one was leaking oil internally and the mileage went up to 36mpg. Not sure how or why as the timing is the same and it even runs the same.

[crusher773]

check your coolant temp sensor too.

[FestYboy]

check your coolant temp sensor too.

Check out the temp sensor on the intake manifold.
Many members have had issues with performance/MPG because the sensor was bad and the giving incorrect data for the ECU to run the engine.
Green connector underside of intake manifold.

John beat you to it Crusher, the one near the T-stat is just there for the gauge, it doesn't send signal to the ECU.

[navdoc101]

Ordered a Denso O2 sensor from Autozone. $29.99, cheaper than Pep, NAPA, & Advance. Will be here by Tuesday. See if this helps. Thanks All!!

[FB71]

^^^ really? Last one I got at Advance only cost me $19...?

[FestYboy]

^ uuuhhh you get a discount! Mr. "I have a comercial account". :p