Rather Poor mileage

authentic · Post by **authentic** » Fri Jun 08, 2012 9:42 pm

Hey there

So I have recently noticed that I'm getting pretty crap mileage out of my 1991 NA. I did a search and found someone using 1990 MX5 for a Tarmac rally used 43.97 litres over 290 km, which is 15.162 L/100km.

I am using 45 litres over 350km of normal, open road and town driving. That is 12.8 L/100km, which seems like a lot when I hardly go above 4k.

Any ideas?

Cheers

Quick Edit: I should note that I am using 91.

brownie · Post by **brownie** » Fri Jun 08, 2012 9:53 pm

there's your first problem,wrong fuel,how up to scratch is the rest of the car, service wise ?.
plugs
fuel filter
air cleaner
Make sure all the really basic tuning stuff is right in the first place,But crap fuel is a biggie,Orange fuel cap in Japan means hi grade fuel,get it on 95 pump gas at a minimum

Born_disturbed · Post by **Born_disturbed** » Fri Jun 08, 2012 10:17 pm

I have a black fuel cap ha.. I run 98 in mine with a 1.8 swap. Will report how my milage is at the end of this tank.

Also I am a "Spirited" driver

Mr. Shine · Post by **Mr. Shine** » Fri Jun 08, 2012 10:18 pm

Unless you're driving enthusiastically at heavy load, increasing fuel octane won't change much, if anything, unless you're experiencing knock. I don't think NA MX-5s came with a knock sensor either, so your engine won't be retarding timing to mask any knock you'd otherwise notice.

It's certainly worth making sure your spark plugs, plug leads and fuel/air filters are in good nick, though. Making sure your tyre pressures are correct is good, too.

Stevo · Post by **Stevo** » Sat Jun 09, 2012 7:10 am

Thats using far to much fuel. On a recent trip we used 7.5lt/100km. We get around 8.5lt/100km around town.

Furai · Post by **Furai** » Sat Jun 09, 2012 7:33 am

I have found 95 gets better range and runs smoother, 7.3L/100 on trips and 8-10 around town. Everytime I go to Hampton I average10 including skidpan time.

WideOpenThrottle · Post by **WideOpenThrottle** » Sat Jun 09, 2012 9:02 am

Is yours manual or auto? & dont forget the Targa Mx5 is tuned to a whisker! so it will be running optimum.

SLYDIT · Post by **SLYDIT** » Sat Jun 09, 2012 9:03 am

WOW!
i get better mileage than that with my turbo'd MX.
Obvious things to check are airflow meter. coolant temp sensor and oxygen sensor
.
I would be looking at the oxygen sensor first. its probably gone bad.

also Do you have extractors fitted, or is the exhaust TOTALLY stock?

fitting extractors and not upgrading to a heated 02 sensr causes all sorts of crappy running issues

Mad Kiwi · Post by **Mad Kiwi** » Sat Jun 09, 2012 9:46 am

My experiance is most cars i drive use around 11 - 13 l / 100km's.

But one thing I wonder is if you are not always labouring the engine, our 1600 non turbo has no get up and go under 4k and if you constantly drive under that and in a high gear you may find holding a gear longer and less throttle depression will incerease your mileage...

Just a thought. I especially notice this in my mazda 6 wagon, the auto constantly goes to 5th gear and I have found using the semi auto and leaving it in 4th more often has increased the mileage. Not to mention the responsive and thus pleasure in driving it...

authentic · Post by **authentic** » Sat Jun 09, 2012 2:13 pm

I'm going to spend today checking out the air flow meter, o2 sensor, plugs and leads and air filter. I'll have to look up about the fuel filter too.

I don't believe it has much to do with the type of octane I'm using. 91 octane wouldn't get me this piss poor mileage.

My tires are definitely inflated as I have 205/40R17 which are rock hard all the time.

I have a Jackson Racing cold air intake installed with an oily panel air filter. Does anyone know if you re-oil these types of filters, or do you just replace them like you would with a normal panel filter?

My exhaust is stock (I think the previous owner may have fitted a coby resonator).

harlansmart · Post by **harlansmart** » Sat Jun 09, 2012 2:56 pm

+1

See below mileage record for highly modified Miata Turbo, it's doing about 8 litres/100 kms on 98 octane.

SLYDIT wrote: i get better mileage than that with my turbo'd MX.

Tanks 1-7: Fully laden touring
Tanks 8+: Mixed solo driving

Ian · Post by **Ian** » Sat Jun 09, 2012 5:49 pm

You can use eith in the JR CAI. Usually the replacement is a standard type pleated paper filter, but you can use a filter designed to be oiled eg K&N etc
Obviously if you 'oil' a paper filter you will have issues...
Cheers
PS If you don't know how old the fuel filter is, that is the FIRST thing I would replace...a Repco one will be fine.

SLYDIT · Post by **SLYDIT** » Sat Jun 09, 2012 6:05 pm

i still reckon a bad o2 sensor. when they go bad they get slow to react. they might test ok but only a scope ( or ecu data logger) can pick up the lazyness.
for instance when i first fitted my turbo, i reused the old non heated o2 sensor. it didnt work properly and was "dead" at idle due to low exhaust gas temps. i only picked it up because i was data logging the o2 sensor signal with my ecu data logger.
the check engine light didnt even light up nor did the ecu show a fault code.yet the o2 sensor was not working at all. the ecu then went pig rich limp home mixtures...

id change the o2 sensor. (get another from pick a part if you dont want a new one)
i ended up getting a heated o2 sensor from a honda for mine and it fixed the problem

Mr. Shine · Post by **Mr. Shine** » Sat Jun 09, 2012 6:29 pm

This has got me thinking about my fuel economy and it seems it's not up to scratch. I think I may see about changing both my fuel filter and O2 sensor.

Angreal · Post by **Angreal** » Sat Jun 09, 2012 8:52 pm

I generally get something around the 8.5L/100km mark and check most times I fill up assuming my lead foot hasn't been driving which gets about 10L/100km

1.8L no forced induction

authentic · Post by **authentic** » Sat Jun 09, 2012 9:22 pm

Yeah with my previous car, a 96' Celica I was getting 10L/100km and I definitely wasn't light on the gas.

Angreal · Post by **Angreal** » Sat Jun 09, 2012 9:37 pm

Wow 8L/100km. I think I could use this to justify some forced induction :p

harlansmart wrote:+1

See below mileage record for highly modified Miata Turbo, it's doing about 8 litres/100 kms on 98 octane.

SLYDIT wrote: i get better mileage than that with my turbo'd MX.
Tanks 1-7: Fully laden touring
Tanks 8+: Mixed solo driving

SLYDIT · Post by **SLYDIT** » Sat Jun 09, 2012 10:06 pm

i can honestly say that adding the turbo has not added any "noticeable" increase in fuel consumption in fact the cruise mileage is probably better, offset by funtime mileage.

This is probably because of the fact that i am still using the factory ECU with a piggyback ECU. in cruise the car just runs happily on the stock ecus closed loop maps.

brownie · Post by **brownie** » Sat Jun 09, 2012 10:32 pm

re ,the fuel,
91 you get at the pump isn't 91 octane RON,It's actually 85 octane with a bunch of chemicals added to pump up the octane rating.

Japan 's fuel is 91 RON,95 RON and 98RON ,(RON)Meaning thats the true octane rating of the fuel.

Check with your local Mazda dealer and ask what fuel should be in it ,they will tell you 91RON.
Our fuel
91 (85RON)
95(91RON)
98(95RON)
A few of you might remember when Challenge first hit the country the fuel really made the cars go...Singapore fuel didn't have additives,it WAS the true octane.
So yes the right fuel will make a difference,Try it,it will only cost you fuel,it's not as though we are running big block V8's

Mr. Shine · Post by **Mr. Shine** » Sun Jun 10, 2012 12:26 am

brownie wrote:So yes the right fuel will make a difference,Try it,it will only cost you fuel,it's not as though we are running big block V8's

Octane rating is the measure of a fuel's resistance to self-ignition compared to the ratio of iso-octane and heptane required to have the same characteristics. I'm not sure what you're trying to say when you say we have 85 RON fuel with additives to make it 91 RON. If you have a fuel that has the same knock resistance as a 91% iso-octane and 9% heptane mixture, then it doesn't matter what's in it; it's still 91 RON.

Octane rating is effectively a measure of knock resistance, so if you're not experiencing knock in the first place there is no reason that moving to a higher octane rating will improve performance or economy, especially in a car that doesn't have a knock sensor, like the NA MX-5.

Furai · Post by **Furai** » Sun Jun 10, 2012 10:36 am

Higher octane will usually allow for more power though right?

So if producing more power to the same amout of fuel that increases efficiency and means you can use less throttle to do same amount of work?

punkoutnz · Post by **punkoutnz** » Sun Jun 10, 2012 11:13 am

I'll say it again. No way would I run 91 octane in an MX5. Seen so many blown up engines at work due to bad fuel it's not funny. The other problem I have is 91 is so inconsistent. One of our customers did a survey (he's a bit of a geek) and reckons he found anywhere from 83 to 88 actual octane at the pump, but not once did he actually find a 91 pump to have 91 octane fuel. The 95 and 98 was a lot closer though he reckoned, but still not what they were advertising. You might not be able to hear the pinging if it's just on the edge of it's limits, but you will be losing power if it's there, which means you'll be having to work the engine harder which means decreased fuel mileage, decreased engine life, etc.

Spend the extra 6c a litre and go for 95 octane.

Mr. Shine · Post by **Mr. Shine** » Sun Jun 10, 2012 11:24 am

Furai wrote:Higher octane will usually allow for more power though right?

So if producing more power to the same amout of fuel that increases efficiency and means you can use less throttle to do same amount of work?

Only if the engine is tuned to take advantage of the extra octane rating with more timing etc.

Running an engine on 98 that performances perfectly at 91 or 95 won't produce any benefit.

punkoutnz wrote:Spend the extra 6c a litre and go for 95 octane.

I don't personally disagree with this and I wouldn't run anything less than 95 octane in my car, and absolutely if the car is experiencing knock, then a higher octane should be used.

Supposedly though all fuel in New Zealand is sampled to ensure that octane ratings are accurate. I'm not sure how your friend was testing fuel, but possibly he was only testing to find out the percentage of iso-octane in the fuel mixture, which isn't (necessarily) indicative of the actual octane rating?

punkoutnz · Post by **punkoutnz** » Sun Jun 10, 2012 11:37 am

Nah he was testing actual octane. He's one of those eccentric types who's more than happy to go out and spend more than a grand on an octane testing kit just cos he's decided he wants to have a go.

authentic · Post by **authentic** » Sun Jun 10, 2012 1:33 pm

Ok well I'll fill up next time with 95. But I can't imagine that it will change much about my bad fuel consumption.

Rather Poor mileage

Rather Poor mileage

JR CAI

Who is online