rotaryrules

Hello all I recently replaced my speedometer cable on my 88 gxl with a manual 5spd tranny, so I could utilize the trip odometer in order to see how many miles my car gets on a full tank. The results to say the least are horrible. I filled up a full tank of 87 octane arco gas at a cost of $21.00 and set the odometer to 0. At an empty tank I only put 125miles. That's pathetic. Is this normal for an rx7? I drove about half the miles on highway and the other half on the street. What gives? why am I getting such crap gas mileage? What can I do to improve it? The car runs great , it's just getting extremely poor gas mileage. I noticed too that the Idle is kind of high. It stays at around 1k until I drive through all of the gears a few times, then it settles around 850-950 rpms. Any input or help would be much appreciated. Thanks in advance------Ren

xxxbadassfoxxxx

well these engines are supposed to use 20% more fuel than piston engines do. mine gets around 16 to 18 miles a gallon on average...but your gettting like 10 or less...could be lots of things thats making that happen
1. oxygen sensor
2. exhaust leak
3. fuel filter
anyone else know anything else it could be? i know im missing a bunch

as for the idle...mine also did that..mine fluxuates from 1000 to 1500 when its warming up and then settles at 750 after its done warming up but if its constant try adjusting the idle...its right next to the "mazda 13b" engraving on top of the engine...there should be a black cap on it...good luck

slow87turbo

well are you in 5th alot? and does your shift light come on in 5th? if it does then you car is not runing to the max fuel economy becouse if your in 5th and under i think its a 1/4 throttle it retards the timming and gives les fuel hence better fuel economy....but damn man i get about 150 to a tank and mines a TII. try that or get your injectors cleaned.

ponykiller

hmmm.. Go with a new O2 sensor. Let that run for a while, and if nothing gets better, then try the fuel filter - per xxxbadassfoxxxx.

OC_

i get about 250 to a tank, with my S5 n/a driving conservative. but i think S5's have a larger gastank. Also, do you do a lot of stop and go driving? Do you have a heavy foot? Maybe you have fouled spark plugs, wires, so on. I got a huge loss of mpg with under inflated tires.

xxxbadassfoxxxx

what would you consider underinflated? how low?

Bigretardhead

last time I filled up I got 222.2 miles on the tank

rx7 adict

my rx gits about 250 miles on tank and it has bad cad converter

Icemark

Plugs, filters, O2, and your foot all will effect gas MPG.

How much oil are you burning through... a good indication of driving style is how fast you use a quart of oil.

For example this last week I drove back and forth to San Diego twice (about 550 miles a direction) and used about 1.5 quarts of oil, and averaged around 20 MPG, and averaged around 75 MPH (whcih actually comes out to quite a bit of time at 100-120 MPH to make up for the slow traffic in LA and SD).

By no means I would consider my driving conservitive. But if I had only used a quart or less, then you could tell either something was wrong with my car or a was driving like a granny.

On the other hand if I was using more than 1 quart every 1000 miles, again ether something was wrong with the engine, or I was driving with my foot way to heavy for good mileage.

13bpower

I averaged 24 mpg in my vert until I put a new engine in. Now it is around 19 or 20. Kinda wierd being the engine with 150k gets 24mpg and the fresh rebuild with 10k miles gets 20mpg. What could cause this?

88 SE

I get 20-22 mpg on my like-new 88 SE

Thats including a rebuilt engine, all new injectors, o2 sensor, clutch, alternator, all belts, all hoses, all vacuum lines etc etc essentially a 100% stock condition engine

My mileage seems to have increased slightly after changing to a cone filter also.

GlenL

Why does an old fuel filter cause low gas mileage?

WookeysRX7

cause it could be clogged, they need to be changed just like an oil filter, except not as often!!

saltlakebay

I average about 17 MPG on my 88TII with mild mods. Thats driving pretty hard most of the time. I'm sure it would be more with all highway.

Try this way for a more accurate MPG reading:

Top off your tank lettting the pump turn it off. Set your trip to "o" - Drive around and let your tank fo to about 1/4. Go back to the gas station and fill it up letting the pump turn it off again.

Check your trip reading. Now look at the pump and see exactly how many gallons were put in. Take the exact amount of fuel you put in and divide by the miles you went.

This will give you a better MPG reading

I agree with the others:

1) make sure your o2 is connected and good.
2) good spark plugs?
3), etc..

GlenL

If a fuel filter gets clogged, why does that lower mpg? It would seem like less gas is getting to the engine. Does the car try to make up for it somehow?

Icemark

The ECU tries and compensate for the lower fuel delivery and richens the mixture.

SpeedyRotary

where is the screw to mess with the idle on a 88 TII???

casio

i had my idle adjusted on my 91 n/a by don at marvelspeed. just from him messing with it for less than 2 minutes, i went from 14-15mpg to averaging at 18.+mpg. i've had 18.1 and 18.3 mpg the past 2 times.

dr0x

The mixture adjustment screw is just for idle. It will make a difference, but I wouldnt imagine 3-4mpg. Not calling you a liar or anything, I just wouldnt expect to see that much of an improvement on every car.

Thaniel

Clogged exhaust, dragging breakes, Broken fan-clutch, Alternator/PS/pump Idler pullies dragging etc. Lots of things can ruin fuel mileage. Got to keep checking.

I get 19-21 on a combined city/country travel to and from work.

1987RX7guy

iTrader: (3)

Driving like a wild monkey I get about 280 mile to the gallon in my 87 n/a but I have yet to check the mileage after my exhaust but I will have the numbers soon like in a week.

SureShot

WOW - you must have one on those magnet things clamped on your fuel line!

86J

I get around 350km on a tank. about 50L when filling up.

GlenL

If you still have your BAC, it's on there, facing out the passenger side. If you ripped off the BAC, then use the throttle stop screw, located on the back of the TB, near the firewall where the throttle cable connects to the TB. ReTed has a nice pic:

http://fc3s-pro.com/TECH/HOWTO/TPS/tps.html

Cool, thanks for the info.

eljefe62

"I averaged 24 mpg in my vert until I put a new engine in. Now it is around 19 or 20. Kinda wierd being the engine with 150k gets 24mpg and the fresh rebuild with 10k miles gets 20mpg. What could cause this?"

I believe an older engine will have more carbon build-up, thus causing a better compression and a better seal
could be wrong in your case, but...