Kento893

Ok, I realise Rotors are not good on fuel and I have no problem wit that. Now, here is my question,

I have an 88 Series 4 N/A, no real mods re the engine, pretty basic set up, brand new rebuild, new plugs, leads, seals, the whole shibang, stock exhaust, stock ecu. (18 Inch rx8 rims, yes thatl affect my economy i understand)

Now, Ive read a few threads and it seems 15MPG would be a figure to look for roughly and Id be happy with that. Now, Im getting 250KM out of 48L around town, which is 12MPG for u guys.

Ive had as much checked as possible around here, not alot can be done, Im kinda running out of ideas of what it might be, any advice at all? Shouldnt be the ECU, its stock. Now I did have a microtech before it, which failed, would the old set up have any effect on any other component? Um, could it be, air flow meter, fuel pressure regulators? etc etc.. Noone around here seems to be able to have any ideas or any equipment to check it.... Is there something obvious Im missing or is easy to check?? Or may I have to go to a proper place with all the equipment to tune it....

Its just I would like to get it rectified soon as It is costing me every time I fill up, and Itd be nice to enjoy a nice rebuilt rotor without any worries. if thats possible!

Any help would be great, cheers.

RETed

How hard do you drive it?
I mean, if you're constantly revving to redline and mashing the throttle all over the place, I wouldn't be surprised you go down to about 10mpg.

15mpg would be "city" driving, but not redlining...

Gas mileage tanks if the tach sees the right side of 4kRPM constantly.

If this is not the case, check to see if the O2 sensor is working correctly.
Also, check the water temp and air temp sensors to be in spec.
Good (i.e. new) spark plugs should help.


-Ted

TongassT

Bigger wheels/tires introduce more speedometer/odometer error. If it was up by +10%, you're actually getting 13-14mpg. Don't know what size tires you're running so Im not too sure about it.

Dive the car on the freeway, trying not to use the brakes. After a while, gently and slowly pull over to an exit and touch your wheels. If one is hotter than the others, you have a dragging brake.

petex

wheels should not affect you gas mileage that much

i have 88 NA as well an im getting 20mpg city/hwy mixed


if you're getting 12mpg there is something wrong.

just one quick question. does you gas gauge shows less and less every time you get in the car?

few things, check your injectors, if old might be partially stuck open. also your ecu might be not engaging close loop mode. few possible reasons. thermostat, engine never warms up. water temp sensor (not sender). o2 sensor. afm is possible but that affects idle so you would know. also look for intake leaks. also exhaust leaks before cat will affect gas mileage.

you can check voltages for all sensors at the ECU per FSM

you could also get WBO2 to confirm AFRs

Acesanugal

iTrader: (5)

I get 23-24 mpg on average. That's one or two redlines a day.

Kento893

Nope, Gas gauge does not get less every time I return to the car..

Barely ever redline it, usually changing below 4K.
Injectors have been cleaned and Tested per rebuild
Spark Plugs are new per rebuild
O2 sensor has been checked per rebuild
TPS checked per rebuild
Thermostat works alright, is warming up as per normal 1/4 Up the gauge
Idle good, shouldnt be AFM
Tyres are 18 inch so yes that has some effect, but not this much I believe.

I am thinking it may be that closed loop mode on the ECU, that was installed new during the rebuild. How may i be able to check that..

Il go and check those voltages with the FSM.

No mechanics around here have any idea or can offer any help which is disappointing as I do not have the best knowledge on do it yourself stuff.

Anything else that mite be it, especially sometihng that may have been changed during a rebuild??

ALso, with having a microtech changed to a stock ECU, is there a change the sensors aren still sending the microtech info to the Ecu..

RETed

Per rebuild?

How much miles (kms) since the rebuild?


-Ted

TongassT

Off the top of my head, the sensors that the ECU cares about are:
The AFM
Boost sensor (located on right hand strut tower)
Atmospheric Pressure sensor (located in right hand kick panel)
TPS
Intake air temperature (located on intake piping after intercooler/before UIM)
Water thermo sensor (green one located behind the water pump)
O2 sensor

I'd check that these are mazda parts and are connected properly, along with checking that proper voltages are getting to the ECU (look in the FSM for this). Locations may be different for RHD, I'm not sure.

SDrotary-FC

at least pull the plugs and see if you are running waay to rich.
(i get over 20mpg mixed)

wogboy_9000

I've got 100,000 on my NA series 4 RX7.
New spark plugs, leads, oxygen sensor, fuel filter, replaced AFM, oil & coolant.
TPS is set perfectly.

Daily driving around town, not driven above 2000rpm, ill get about 16l/100km or 14.5mpg.

katkaroto

i drive my S4 GTU around so so... and i get a nice 25MPG for mixed driving. anything lower than what i get, i'd prefer driving my tundra around.

Kento893

Dam totally forgot about pulling the plugs, will do that asap.

Its done... less than 2000KM since rebuild, so about 1250 Miles. Ive actually had a bit of a research and talked with the guys who did the rebuild, will wait till I have a few more kms on it and see how that goes as engine should set and run a lil better then. That sound right?? First rebuild under my car so.

Will go and check those sensors anyway, I have a feeling they mite not be mazda parts from the previous owner.

Thats some good advice to work on, should help. thanks.

RETed

Yes, I would wait for double the more kms to see if it gets better.
Depending on the rebuild, compression could be still building.
Your engine is still considered "fresh".


-Ted