Chief_MC

Hi everyone!

I have a kind of a problem here!

As far as i know NAs usualy have around 20 miles per gallon, since i'm living in a metric system country i'll count it a bit different: i think it something like 12 liters per 100 km.

but mine's getting like 16-18 liters per 100 km!!! I think it something around 13.5 MPG... (And to be honest it's not worth those 16-18 liters, 'cause my friend's '94 Celica GT w/ 138HP is blasting my REX7, athought his mileage is around 11-12 liters per 100 km)...

The question is: what could be the 'cause of this catastrophic mileage? Something is definitely wrong with the fuel system, firstly i though it was injectors, but after i cleaned them gas mileage stayed at the same level.

I have a minor mods done to the car like downpipe and hi-flow cat, also i have a locked 5th and 6th ports (which i plan to unlock)...

My only guess is that it could be the fuel pulsation damper malfunctionin'... It's not leaking, but one technician told me that i have all signs of a bad pulsation damper, like a big loud POP from the exhaust when i'm suddenly decelerating from a high RPM...

ANY help would be greatly appreciate!!!

Thanks!

Bambam7

Don't listen to that mechanic, what he just said makes absolutely no sense at all.

13.5mpg in the city sounds about right to me. They get a lot better on the highway.
Try to shift under 3800rpms
One other thing- check and/or replace your o2 sensor. They degrade pretty quickly with rotory heat, returning a lower voltage than is accurate, inviting the ECU to dump more fuel in. Don't get one from a dealership, but from a parts store, it's a universal bosch 1 wire sensor.
There are a few other emmisions related things that can affect fuel economy, but soince I rip all the emmisions stuff out of all my 7's, I can't help you out there!

Icemark

US EPA for the FC is only 17 MPG city. Most people only average 15 MPH city cycle, so your 14 MPG doesn't sound that bad. Have you replaced the O2 sensor yet, as an old one, or one that has been operated with poor quality or leaded gas will cause the mileage to drop pretty radically.

The PD has nothing to do with the loud pop on lift throttle. The technician does not know what he is talking about.

The loud pop is either from an untuned car, bad ACV, or bad sparkplugs.

Chief_MC

Forgot to say it also my car is idling roughly and sometiems stalls after accelerated warm up cycle, if started cold (also wondering why is that happening, i've read somewhere that it could be the BAC valve filled coggled with some dirt)!

Thanks!

harjms

Whens the last time u got the 60K tune up? i believe doing this will help(if u havent done it in awhile). as in plugs, wires, etc... but im no mech..so idk...just thought i would throw an idea

razorback

i get 8 on my untuned half bridgeported t2..

Digi7ech

iTrader: (1)

I get 18mpg on the highway so don't feel too bad. I have a lead foot though hehe.

Clean your spark plugs. and it may help. It fixed my idle and gave me maybe like 1 extra mpg.

Another thing might be that your plugs on in wrong. Maybe you have the leading and trailing mixed up. CHeck them out.

The housing will say L and T next to the holes.(I think Trailing is on top)

Chief_MC

Thanks for quick response!

Hey BamBam7 is there any good resource how to get all those emissions stuff out of my car?

And Icemark, i have changed the spark plugs 3k km before and mileage is not better since than... And i could you tell me a little more about what could be wrong with ACV and how to indicate a problem with it? I think i must say that a pipe that went from ACV to pre and main cat is now dumped in the air since i have a custom hi flow cat...

Thanks!

88IntegraLS

I agree with Icemark that the O2 sensor could cause the bad gas mileage, among other things. I doubt the pulsation damper has anything to do with it, but the fuel pressure regulator might cause poor MPG if it is stuck or something.

A friend of mine was with a GXL and after market exhaust is right in the same MPG ballpark as you. My NA is doing 20-22 MPG in mixed city / highway and occasional hard driving, but it only weighs 2400 lbs and has (really light) 91 coupe wheels. Light vehicle weight, low rotating mass, and low exhaust restriction help increase MPG. Good engine compression and having the air flow meter mounted horizontally (like stock) also helps. If your wheels are badly out of alignment or tires underinflated, it can cost you a mpg or two.

bcty

this will tickle your ***.. right after my friend got his big street port done on his 90 n/a during the first few break in periods he got 750km per tank!

andrew lohaus

does the o2 sensor realy affect city milage that much? i thought it only realy mattered at low/constant rpm. which isnt exactly city driving

Icemark

Everything but WOT

5 point whoa

I get almost 16, but used to get 13. I put mmo in my gas, and down the top vacuum hose every once and awhie, and it cleaned out the fuel injectors, and the engine, and I get better mileage

JKM

Heh, thanks I've been meaning to search for that seeing as my car does the same thing. Been meaning to get a full tune up done for a while now, although technically it shouldn't need it yet... IF I trust the previous owner (which I don't )

Blowtus

chief, on a stock t2 I get 10L/100km on the highway and 15L/100km around town. The non turbo engine should do a bit better than that.

Amur_

9.5l/100km on the highway.

https://www.rx7club.com/showthread.p...hreadid=212848


City mileage is half that (~300km to a tank...)

wai

I only get 10~12mpg

Chief_MC

Yeah, i think i need to try to replace O2 sensor, 'cause i didn't yet...

Hey BCTY, did that guy only was riding on a highway? I have had a 8.5 liters/100 km on a highway when i've bought the car... But know i'm not :-(

Blowtus! I have had a 12 lt/100 km in mixed city/highway... but know it's 16!!! I can't stand that ;-)

And can someone tell me please what can cause that loud pop from the exhaust when i'm suddenly steppin' out of the accelerator pedal when engine is on 6.5 or 7k RPM? I'm worring about that a bit...

And i want to say Thanks to everyone! This forum is simply great! I have absolutely no other source of good reliable information about my 7... There are only 2 RX-7s running in my city at the moment!!! One is mine '88 GTU and the other is black 3rd Gen i think '94 or '95 (i think owner does not cares it good), i don't know the onwer personally yet... There are more of them, but all with blown engines! Since engine overhaul costs here are pretty high nobody doing that, and you can see a couple of 2nd gens here with 1.8 or 2.0 Opel or Audi engines, but that is completely different car though... I feel like i should say that Kiev is 5 million city for you to undestand how exclusive my car is here :-)))) Altough there are a couple of RX-8 already in the city... But i can't even compete with them at the moment :-((

Amur_

It's called afterburn. Your motor is spitting out unburnt fuel and it's igniting in the exhaust system with a bang. It's normal and harmless. Mazda installed a valve to try to eliminate afterburn, but it doesn't always work (as you may have noticed.) Just enjoy it.

astrochild7

iTrader: (3)

get your 5th and 6th ports to work like they are suppose to and your gass milage will come back....wiring them open kills your bottomend torque / milage...

M.C. Language

Your ports are Stuck!!?! ****, after i opened my intake and got my 6 ports all goin again, my power increased drasticaly! and my mileage went way up! YOUR CAR ISNT GETTING THE AIR IT IS SUPPOSED TO HAVE, thus killing power and you are not getting the right air to fuel mixture.. a celica gt... Not a gts? if its just a gt you should blow his doors off... even the GTS's are Not all that fast.. fix your ******* ports man, you have a new car...
those Ports are what a VTECH is to a Honda, take away the vtech, you take away the power...

Chief_MC

Yeah, it is a GT with only 136 HP and i can't compete with it... Shitt! I positivley need to fix that ports, but i opened up my exhaust and now there will be absolutely not enough backpressure to open the ports anyway... I need to find some cheap solution to open and close them somehow... I know that there are a couple of them (solutions)...

By the way the guy that owns that Celica just ride my REXy and found it way more maneurable and controlable than his Celica GT... I was really pleased to hear that :-D

Oh... I just a half an hour ago i raced with Honda Prelude 2.2i VTECH... I think it has 183 HP... His beated me... ****! I think the first thing i'll do after New Year's Eve will be fixing of aux ports :-)

Happy New Year to everyone!

Chief_MC

Ohh... Guys... Forgot to ask one more thing... I was always thinking that 3800 hesistation problem is a Turbo II common problem... But yesturday i found that my GTU is also on the list of cars that has that problem... Is that possible?

I think i should desribe how it feels... My car starts like big inhaling air at ~2800RPM (lower than that it is really weak) and climbing up and you have an impression that it will be pulling harder and harder, but suddenly at ~4000RPM it starts to just slightly and instable raising the RPMs and it feels like it hesistates for further accelaration... Is that a famous 3800 hesistation???

Also after driving for 2 weeks Mercedes 200 (carburator one, W124) i have an impression that my 7 has absolutely horrible low end torque...

****! My car is really full of problems!!!

13bpower

Its an N/A rotary, it will never have alot of low end torque. BUTTTTT, get a new o2 sensor and fix your ports, or wire them open for now, and you will see where all the HP is in you car.

Broke 6th ports in a N/A will make it slower than anything else on the road.

Chief_MC

I replaced my O2 sensor with Bosch one and i think the one that i took out was never replaced and it was a NGK one... i noticed a slight difference in reaction to pushing the accelerator... And i did the TPS adjustment... not sure that i did that completely correct 'cause there is a half of rotation of that screw between 1 and both lights are led...