Very Low Gas Mileage!
 

Hello Everyone
I'm on my fith month of ownership of my 1996 Montego Blue Miata.
Got it in August 2013 (a bad time to buy a roadster)
With 159K miles and folder full of receipts from the 9th owner
Car ran like clock, I'm in New England and my "Eunos" came from florida 2 years ago. The day after I got it I drove it to Cape Cod.

Did 260 miles on 9 gallons. Was very happy with that efficiency

After that and until now car was doing anywhere from 18 to 25 mpg based on driving manner.

Today I stalled out after I did 39 miles on 3.5 gallons. That gives me an average of ready?
12MPG in the Miata!!! With recent oil change, completely stock, with every seal and gasket replaced within last 2 years accord to the repair logs and receipts.

In November car started to consume some oil. About 0.5-1 quart of oil per every 1000 miles. During a last oil change I noticed an oil leak that seemed to be coming from CAS O-ring. The CAS O-ring was replaced in late 2011, and CAS itself was replaced (does that always mean new gasket?)

Car runs very strong, engine is stable and powerband is consistent. The question is how come this miata is so hungry.
New OEM CAS-O ring should be here anyday so I can replace it (hopefully to eliminate or reduce oil consumption

What Can Cause 12MPG???? Weather? Cam Seals?

HELP THIS MIATA GET BACK ON TRACK
https://www.miataturbo.net/attachmen...ine=1389328346

Fill the tank full, drive 50 miles and refill. I bet something else is going on.

Consuming oil? Start with a compression test, then move on to the narrowbands.

Will do that

and

Would you please elaborate on what fillinf it 50 miles after filling it would shine light on?:idea:

Theres miatas that seem to have a problem filling up the tank fully or perhaps even a leak. I think thats what hes talking about.

Also note the plugs when doing the compression test. Take pics.

Will run to autozone rent a tool and do a compression test first thing in the morning.

Found This:
by Keith Green and miata.net

Not absolutely 100% sure if it's the same for a 1.8 engine, but on my '92 the specifics for doing a compression test are as follows (from factory manual).

1. Check battery is charged.
2. Warm up engine (normal operating temps).
3. Shut off & remove all spark plugs.
4. Disconnect the ignition coil connector
5. Hook up compression gauge to cyl #1
6. Fully depress accelerator pedal and crank engine
7. Record max reading
8. Repeat for #2-#4.

Minimum is 135, maximum difference between cylinders is 28 psi.

9. If compression is low, pour teaspoon of oil in cylinder and recheck.
If compression improves, it's the rings/piston/cylinder wall. If compression stays low, it's the valves.

If the compression in adjacent cylinders stays low, the cylinder head gasket may be defective or the cylinder head distorted.

Reconnect ignition coil connector and reinstall plugs when done.

Sounds about right?

Pull the injector fuse too when undoing the coils.

Either the pump clicked off early or you've got a leak.

I've managed a legitimate sub-13mpg average over a full tank in a Miata twice, but the first time was 100% in-town driving with lots of, erm, enthusiastic driving, and the second time involved nearly 90 minutes of in-boost cruising at unmentionable speeds.

At 13mpg the spark plugs are probably coated in an inch of crap.

I tend to think this is the case.

I don't feel like a single fillup after 39 miles of driving is enough to justify looking for something wrong. I'd definitely fill it up, drive til empty, and fill it up again and see what kind of number you come up with.

The 18-26 results seem pretty standard on a stock miata to me, especially with some spirited driving. Also of note, the stock ecu hates high rpm cruising. Once you pass ~4000rpms they go stupid rich regardless of throttle position and that will kill mileage.

That's a thing, If I pass 4000rpm I go all the way to 7200 but that's a rare occasion.
On a daily I usually shift at 3-3.5k rpms.
Two autozones didn't have compression tester, but they found me an autozone that does, so that's where I'm going now. (Will take Pics of Spark Plugs as Well)

And If the Pump Clicked Off Early, how do I go about it exactly?
(New Pump?)

Tnx for responses everyone.


offtopic I had an integra that had 172k miles, barely maintained by previous owners, was overheating and was burning oil. I pushed everything out of it but never did less than 28mpg. After that I had a 5spd v6 camry that I used to work at a transportation company. It was burning oil as well, it was a quad cam v6 and was doing steady 23-25mpg. So it's definitely not my driving! I know how to conserve gas, but even when I do miata consumes it for me...

And I was also always wondering.
First of all why NAs never received a low gas light
But secondly, when I put 3 gallons of gas in, the gas gauge barely goes away from E,
and after 10 miles of driving it's on E again an stays there for next 30 miles.
When I put more in let's say 10 gallons the gauge stays where it's suppose to be but regardless I drive last 30-40 miles on E. Every other 94-97 NA is the same way or not?

The NA was made before the majority of the human race became too stupid to glance at their gauges once in a while.

Not a true linear gauge. Also: Shape of gas tank.

Yeah but that doesn't explain it's absence in my '99. Since this is the first car I've ever owned without one, I didn't know it didn't have one until I ran out of gas on I-65 :giggle:

Become part of the solution, Steve. Become part of the solution.

Gas pump, like... where you buy your gas. Shuts off early because of kickback into the filler tube. Mazda actually did a recall on the NB1 for this, and my car does not have the revised parts. After the pump kicks off on me I can usually get another 4-5g into the tank

Then again I fill that bitch all the way to the neck until I can see fuel. Makes for pretty consistant fillups but probably increases fire danger :rofl:

So I did the compression test
It goes to approx 180-190 in every cylinder according to autozone rental tool :bowrofl:
So I assume copression is good
Here is the pic of the plugs
https://www.miataturbo.net/attachmen...ine=1389386102

What's next diagnosis procedure gentleman?

I had a wild guess. May be the timing was advanced on my miata and I never knew? So I'm all running 87 while it want's 93??

As far as I know half tank of gas and half test of fumes is the most dangerous mixture

So I did the compression test
It goes to approx 180-190 in every cylinder according to autozone rental tool :bowrofl:
So I assume copression is good
Here is the pic of the plugs
https://www.miataturbo.net/attachmen...ine=1389386115

What's next diagnosis procedure gentleman?

I had a wild guess. May be the timing was advanced on my miata and I never knew? So I'm all running 87 while it want's 93??

As far as I know half tank of gas and half test of fumes is the most dangerous mixture

Plugs dont look stupid rich, compression is good. You're either sucking at math (or sucking at filling the car up all the way), or have a fuel leak. Or I guess getting your gas siphoned.

OK so, $10 at 3.29 per gallon gives me 3 gallons correct? YES

I did it after I stalled out so gas tank was empty!

3 Gallons into an empty tank made me stall out 38.2 Miles later

38.2/3 give me 12.73 mpg :vash:

If there's a gas leak there should be signs of it on the ground, if not then smell of the fumes? This car never smelled like gas at all and miatas especially with soft top don't gave the best sound/smell isolation either.

SO
I will fill up the tank just because it was kindly suggested to me here.
But I am almost hundred percent sure I will just average 12mpg through the tank full of gas. Like I said I will do it regardless, but please explain me the principle of that improving my gas mileage I am too much of a :noob: to understand

Soooooo as far as I understood filling up the tank will help me to exactly calculate the gas milleage as well as see how much my tank takes correct?

Yes. That's how the rest of the world calculates gas mileage.

So you are saying miata might use different amount of gas based on how much gas there is in the gas tank?

Call me an idiot but only outcome I see out of it is waisting more money by waisting more gas with a poor gas mileage like that. :burncash:

PLEASE TELL ME
How come empty gas tank filled up with a certain amount of gas
and the odometer reset to 0 at the gas station is a less precise calculation, than the same thing except with more gas. American math :dunno:

It's like getting getting blacked out after drinking 0.75L of Vodka, then buying 3 liters of Vodka and still getting blacked out after the first 0.75
(Excuse my comparison, I am Russian)

No, i'm saying that filling the tank up completely is the only way to get consistent repeatable results. You might starve the car in a corner and have it stall for lack of fuel. You might be going uphill. You might be going downhill. It might be hot, it might be cold.

Fill it up to the top and you know EXACTLY how much gas you used. Every time.

It's not the only time I noticed the gas consumtion being so high.
I'm not trying to figure out if my car is doing 29mpg or 30mpg
I'm trying to figure out why over the last 10 times I went to gas station
average gas consumption was around 12-13mpg

I did the compression test, the plugs are good, ok what's next? What else significantly affects gas mileage? What's known to be faulty on miatas and cause such a drastic decrease. That's the kind of questions I came here for. Not to ask how to calculate my gas consumption

It's already systematic. I know what you saying here about precision and accuracy, and I gave it enough tries, put gas enough times and was bitching about it for quite some time now. The only reason I am adressing the issue is because It takes too much gas (I know that for sure) without any apparent or obvious reason

If you won't give us good data, you wouldn't get good answers.

My Miata gets 14-15mpg when my wife drives it.

...
okay
thanks
Sorry more efficient car is the answer

One time I made it 237 miles on what the gauge said was 1/2 a tank, but I was driving north toward the magnetic pole of the planet, so that was helping my car get better gas mileage. My gas mileage was horrible on the way home even though i was driving south which according to the map is downhill.

I know how much those arabs hate you russians so I blame OPEC, its obviously a conspiracy.
























No dude, there is nothing in a Miata that I can think of that would cause such miserable gas mileage that wouldn't show up as some sort of massive performance or drivability hit. (running rough, misfire, etc)

I'll go fill up and while I'm using that gas will be waiting for more (alternative) responses

Thanks everyone

This

You either have a large gas leak, a cylinder that is not sparking, or your injectors are dumping massive amounts of fuel because they are either broken or an o-ring is busted a fuel is spraying everywhere.

Check your spark just to be sure.

See guys

He have a turbo!
And has a response I was looking for!
Thanks EO2K I'll get back with the results

Gas leak sure.
No spark on a cylinder? Plugs dont agree with that.
Injector dumping fuel into a cylinder? Plugs dont agree with that.

If you have good compression and arent showing a loss in performance other than gas milage with plugs that look like yours then you are either leaking gas, driving like a moron, or someone is stealing your gas.

I know noone is stealing my gas.

Now to driving like a moron part.
Well I do like to push it around a little here and there, but rarely getting out of 5000rpms even when I deliberately push it.
Reading what other guys get driving their miata amazes me they complain about high 20s.
So it's either I am leaking gas or all the rest of miata owners drive like pussies.

If you drive a miata like you would to save gas you get shit gas mileage, in my experience. Accelerate briskly up to speed, shift at 4kish.

We all drive like gigantic pussies. You're the only one manly enough to handle a Miata.

How come you interpret everything I saw wrong?
I said the same thing Leafy said except in different words.
I meant if I drive like a moron then others drive like pussies because I don't drive like a moron, and therefore others don't drive like pussies!
Manly enough to drive the miata lol?

My wife gets almost the same kind of gas mileage you do. You're either super girly or she's super butch.


(Don't be so serious)

How Do I make this quote appear under every single one of my posts! :dealwithit:

Copy, paste, add to signature.

I'll give it one more try.
Won't even look at the gas gauge and will drive normally like I would rive my Honda or Acura.

BTW you are from Worchester! Finally someone close enough on big and stable enough miata forum

Did somebody say, "Very low gas mileage?!"

https://www.miataturbo.net/attachmen...ine=1389401297

im doing 12.7 in my miata :vash2:

I understand that the plugs don't agree but I just listed the types of problems that would lead to terrible mileage. If an o-ring was broken and it was spraying fuel from the rail it woildn't show at the plugs and he may not smell it. This happened to me when I put my new injectors in but I had a wideband and immediately found the problem.

OP, if you are driving your miata at super low rpms it is going to get terrible gas mileage. You are loading up the engine like crazy and it is dumping fuel. As stated earlier it is much happier between 3.5k and 4.5k.

Have you checked your tire pressures?

Will do!

Anyways, I started driving it normal shifting between 3 and 4.
Forgot to mention this earlier My car is also idles weird when cold. The gauge might already get to the normal temp but rpms stay at around 2.3k and if I press the brakes it goes up and down from 1.5-2k

Once the warms up everything is normal

I'd check the temp sensor. Not the one that goes to the gauge, but the one for the ecu. If the ecu thinks the engine is cold, it'll run overly rich.

--Ferdi

Where exactly is it located?

Found it. I will be doing CAS-0 ring job one of these days, and will adress the temp sensor as well since it's all back there

Those plugs look fine. I will repeat, fill the tank full, drive 60 miles, refill tank.

Example
Lets see I drove 62 miles, and when I went to fill up I used 1.8 gallons. I take 62 and divide by 1.8 and I get 34.44444444444444444444444444444444444444444444444

The best part of this test is its free, ie you will use the gas anyways. If you have a brain annurism? from the calculations and have to go to the hospital then that will cost you I guess.

"Too Funny" Jacob

Anyways So Far I drove 140 miles on 12 gallons, gauge is pretty much lined up with the E mark.

Local Mivec Enthusiast suggested that gas station use winter blend gas this season (as well as other winters). Not exactly sure what it means or what they change in petrol anyway it's not diesel which may freeze. Might that be the case?

I was driving normally, shifting between 3-4 as suggested

Always better to take a sample of a bigger loop than a small one. AKA a full tank is better than filling up 1 gallon. The reason for that is not all pumps click exactly at the same amount of gas inside the tank. There could be as much as a half a gallon of difference. Some click early, others click late. Same pumps can behaves differently especially if someone topped off their tank before and filled up the pressure sensing unit or whatever you call it. Some will turn off differently based on the angle of the handle into the tank.

That said the 34 mpg number is a meaningless number because the possible error is so large.

This is what i did. I had oil comsumption and bad gas mileage aswell. 1) I cleaned my injectors and replace the injector orings. A real injector flush, not a upper plenium cleaning. 2) replacd my 02 sensor. It was lazy. 3) for the oil consumption i replace the valve guide seals.

While your plugs don't indicate running rich, IF YOU WERE actually dumping that much fuel into your engine you would surely smell it in your tailpipe. Start your car and let it get up to temperature. After it is warm, place your hand in the exhaust stream for 30 seconds... Walk inside and let your wife smell it. Serious (kinda).

If she smells heavy gas smell then one way or another that gas is passing through your engine. I imagine this would also be accompanied by black smoke on acceleration? If your car isn't passing that unburnt gasoline through your engine than your gas has to be going somewhere.

Buy some gasoline safe UV dye and place it in your tank before you fill up next time. Drive about 50 miles and put it in your dark garage on jackstands and use a UV light to look for leaks. That should give you a good idea where your gas is going.

Do you let the car warm up before you drive or do get in and go?

Put in a new Thermostat. I had a 160F and found when it's 30F out the car didn't warm up enough, killed my gas mileage and threw a O2/Cat code. I've replaced it with a 180F. NAPA $6.