Help!!! I am getting REALLY terrible gas mileage... 13mpg on highway! I think that the ECU thinks that the car is running cold all the time. could this cause that bad of gas mileage? where should the temp gauge be getting to?

 

Temp gauge should go about a 1/4 of the way up. Don't feel bad my N/A Got only 160 Miles on my last tank of gas. HEHE

 

you might have to adjust the pressure on teh skinny pedal on the rght. Thats a last resort though

If the car idles at 750 (it IS the same for TIIs isn't it?), then it thinks it's warm enough. Could be a lot of things but from what I recall reading, that's not all THAT bad...

 

Mileage on the highway is usually pretty good. If you are getting bad mileage on the highway, it could be a few things- but probably related to the ECU or o2 sensor.
My guess is that your car isn't going into closed loop mode.. or if it is, the o2 sensor is very worn and returning too low a voltage.
Replace the o2 sensor.
Or, if you have a way of checking the voltage from the wire while you are driving, you should see it fluctuate quickly between about .2v and .8v at around 1/4 throttle... cruising. (this is closed feedback loop) Also, under full throttle, it should read about .9v. If it reads lower numbers, or doesn't fluctuate at cruise, replace the o2 sensor. BTW, DON'T get it from mazda!!! It's wayyyy to much money. Just get one from any parts store... it's the same sensor.

Also, check the ECU for engine codes.
Check the pressure sensor as well (pass. side shock tower), because thats a main contributor to switching into closed loop (detects vacuum)
One more thing- just check the TPS, it's a simple test, if it's way out of alignment, your car may not go into closed loop either.

 

That IS bad for highway mileage. I was getting 18-19 MPG in combined daily driving and about 22 on the highway in my '87 TII. Check your TPS, O2 sensor, plugs, wires, air filter, and exhaust system (clogged?). My car had no cats and new 02 sensor/plugs/filters.

Todd

 

heh welcome to the life of the rotary owner. Getting 11 mpg city and using 93 octane I'm sure I could get a little better gas mileage if I kept my foot off of it...but what's the fun in that :fire:

 

Time for a tuneup

 

here is what I have done already:

new o2 sensor, tested working.

new engine.

new air filter.

TPS... can someone tell me how to check that? my idle does seem kinda sticky. its favorite positions are 2000, 1500, and 800. it sticks @ 1500 most of the time. Temp gauge gets up to 1/4 after about 10-15 minutes of driving.

I have new spark plugs, so I am going to try those as soon as I get some time, and its not so friggin cold outside.

Its also possible that its the cats, new exhaust on the way that eliminates those though.

 

how new is the engine? maybe milege will increase after broken in.

 

new engine has over 800 miles on it. It has new apex seals and rotor housings, plus everything else new that you would do for a rebuild.

 

I bet that you will be OK with the plugs and exhaust. Be sure to test/adjust that TPS (try fc3s-pro.com) the directions are on there.

 

Im having the same problem with mine what is the average MPG it is supposed to bet getting. Does anyones car hesitate at 5k rpm with in 10 mins of starting it and driving?