i haven't seen this bad mpg during my entire life. i know FD consumes a lot but thats to much. i see single digits durings city driving is this normal? how can i diagnose? i searched and found some info but not that much. i will replace O2 sensor but whats next? my car has only intake and exhaust

 

plugs, wires, and fuel filter to name a few...

 

For max Mpg ~ New intake filter/s,Plugs, Wires, Fuel Filter, Oil change, Oil filter and if your stock an 3 inch Stainless steel downpipe with a new 02.

Also an alignment, if your wheels are off your straining the car every time you drive.

 

wideband replaces stock O2 or it is installed somewhere else on exhaust manifold?
PS: i searched and found that people install them on various locations but what i want to know, can it replace stock O2

 

I'm not sure about replacing the stock O2 but I know the O2 should be attached to the downpipe not the mani. I'm pretty sure you can run without an 02 but for mpg purposes I'd use it.

 

I believe you misunderstood him. He ment get a new downpipe and also get a new O2 sensor, not get a wideband to replace the O2 sensor.

Replacing the O2 sensor will parobably help a lot but if you do everything lhe listed, it'll will improve your mpg the most.

 

I understood him, i just wanted to know if i can install wideband O2 instead of stock O2

 

Oh. Sorry, it sounded like you did.

Well i'm not sure if you can run the car without one but if you did run a wideband, you would want to run the sensor either near the end of the downpipe or somewhere in the midpipe (if you have one).

 

If anything have a second bung made it will be worth it.

 

Some wideband systems have a "simulated" narrow-band output that can be used in place of the stock O2 sensor. But the wideband sensor will last longer if you install it in a 2nd bung that is further from the engine.

Tire pressures also make a big difference in fuel mileage.

 

uh how about a list of modifications?

 

If you have a PFC, you can turn off the stock O2 sensor and run strictly off the tuned map. At that point, you could install your wideband, run it through your dataloggit(assuming you have one) and tune your map.

On a side note, if you have a PFC and Commander you can check to see if your O2 Sensor is working by going under etc. in the menu, then to "sensor check" It will pull up several different sensors. Find the O2 sensor. If memory serves me correctly, I believe it is at the bottom of the first column. If I remember right, the "perfect" voltage is .45. This is what it will try to maintain. Anything above that is more rich, anything below is more lean. It will go all over the place when driving, but you can kinda check it out when you are driving. If it is like 1.5 or so, you are prob. running pretty rich and this could be a partial cause of your problem.

 

I dont have power FC. so can i unhook stock O2 sensor, install wideband O2 in its place and hook stock wires to it? I'm saying this because if my O2 is bad, i could go and get wideband and install it instead of stock sensor and not spend extra on 2 sensors. will my ecu understand it? and how will this affect my MPG

yes i'm probably runing waay too ritch. my car smokes hard when cold and this smoke smells fuel. when warmed up smoke dissapears completely but exhaust always smells fuel. you can see warmup on the vid: http://www.youtube.com/watch?v=qxxMf2V-lS4

 

engine itself is stock. The car is JDM so it shouldnt have a precat. mods are dual intake and exhaust.

 

No you cannot. Just replace with a new stock O2 sensor. If you have the powerfc then you have the option of turning off the feedback on the stock 02 and run programmed fuelling.

So to simply answer your question, just replace your existing 02 sensor with a new stock 02 sensor.

 

thanks.
I was looking for them on ngk.com. looks like they have 2 types: OEM identical and universal. they say OE identical has 4 wires but doesnt RX7 use single wire sensor?

 

A stuck/sticking/dirty Injector will also significantly reduce your MPG, maybe worth it to get it flow tested and cleaned... as memory serves this is fairly inexpensive, and could save you from purchasing new injectors...

-DC

 

DCrosby
Thanks, i will do that as well

 

While DCrosby is correct, getting to the injectors on a fairly stock car is not trivial. They cannot be tested and cleaned while installed on the car, they need to be removed for that. I would wait and use that as a more drastic troubleshooting step AFTER doing the standard maintenance you should have done when the car arrived:

* Change spark plugs
* Examine plug wires to see if they need to be changed
* Change O2 sensor
* Air filter replacement
* Oil change and filter replacement
* Fuel filter replacement
* Coolant flush

I would also go ahead and run a bottle of some fuel system cleaner. Once those things are done, observe your fuel mileage and see if it improves or not.

 

Thanks for input. I'm kind of afraid of those fuel system cleaners. people say if you pour it into the tank, it can take all that accumulated in the tank during these years into injectors. is this statement correct?

Oil and oil filter are changed
plugs were just a bit dirty but i cleaned them.
plug wires are ok, i just visualy examined them, no cracks etc. what other test procedure should i use?
removed both air filters, i will put new foams there.
already bought a fuel filter, it's hard to get there thats why i havent replaced it yet
haven't done a coolant flush
dont know about O2, i want to change that too.

did you see my video? i think my car runs very ritch. what do you think?

 

Well, for starters, rotaries just run richer for the most part by nature. I didn't see your video, are you kicking smoke? Or what is causing you to think it's running too rich (aside from your gas mileage)?

Most of those things on that list should just be replaced. The simple that you have no idea the age on the components. If I were to by someone's FD today, unless it was a close friend's car that whole list would get done above (and probably a few other things).

For the spark plugs and wires, there is no reason NO to replace them really. They aren't expensive and it will give you a base to start your maintenance records. Problems with either can and will have a huge effect on the car's power levels as well as it's fuel economy.

If you really have sediments in your tank which are harmful, they are going to come out with or without fuel system cleaners. However, it's more of an old wise tale. Many owners here have good results with BG44K injector cleaner.

You need to get ALL the maintenance out of the way first. If things aren't different after that, then you may have an issue which requires a little more troubleshooting. However, you need to get the standard stuff out of the way first.

 

Mahjik
thanks. i will order plugs wires and O2 from NGK. by the way, which NGK O2 sensor should i get? 4 wire or single wire? they say OE identical is 4 wire but as far as i remember RX7 uses single wire.

As for fuel system cleaner, i will try wurth. thats popular german company. produces oils, different cleaners and stuff like that.

i think it runs ritch because exhaust smells too much fuel. it definitly runs waay ritch above 4500 as my secondar not kicking in. i'm planing to instal wideband and O2 gauge after i'm finished with all this maintaince stuff. video is here: http://www.youtube.com/watch?v=qxxMf2V-lS4

 

Singe wire is fine. You'll just need to cut the OEM connector off the OEM one, and splice it onto the replacement.

 

Looks like it's cold, and the Youtube Smellavision server seems to be on the frits today An Overly Rich Smell when Cold (Outside) and a Cold Motor is common...

The fuel filter will tell you, once you remove it, how much gunk is in there, and weather or not the injectors might have seem some of that dirt... If the fuel before the filter is black as Coke, that's bad... and likely that some of that got into the injectors.

Not properly boosting past 4500 (the transition between primary and secondary) would also make descent gas millage impossible since the ecu is fairly stupid, and will probably add fuel based on RPM / Load, and boost. If boost pressure isn't there then it still might dump fuel to preserve the motor...

maybe someone more experienced with the stock ECU can speak to this.

 

other possible causes would include miss installed vacuum hoses.

I worked on an FD recently that had a check valve between the FPR and the manifold, causing the FPR hold boost pressure compensation when at idle.

Ive also seen cars that had the FPR hooked up through the factory enrichment solenoid to a boost source that wouldn't see vacuum, while not nearly as bad as the above car it still ran rich as hell and got shitty gas mileage with 4-5 PSI more fuel pressure than what its supposed to have in the low load areas.