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Old 01-10-2014, 12:32 AM   #1
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Unhappy 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
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Old 01-10-2014, 01:00 AM   #2
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Fill the tank full, drive 50 miles and refill. I bet something else is going on.
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Old 01-10-2014, 01:03 AM   #3
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Consuming oil? Start with a compression test, then move on to the narrowbands.
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Old 01-10-2014, 01:15 AM   #4
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Quote:
Originally Posted by triple88a View Post
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?
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Old 01-10-2014, 01:18 AM   #5
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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.
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Old 01-10-2014, 01:21 AM   #6
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Also note the plugs when doing the compression test. Take pics.
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Old 01-10-2014, 01:38 AM   #7
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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?
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Old 01-10-2014, 01:53 AM   #8
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Pull the injector fuse too when undoing the coils.
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Old 01-10-2014, 01:54 AM   #9
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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.
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Old 01-10-2014, 01:55 AM   #10
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At 13mpg the spark plugs are probably coated in an inch of crap.
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Old 01-10-2014, 08:29 AM   #11
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Quote:
Originally Posted by Savington View Post
the pump clicked off early
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.
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Old 01-10-2014, 12:44 PM   #12
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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...
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Old 01-10-2014, 01:06 PM   #13
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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?
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Old 01-10-2014, 01:10 PM   #14
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Quote:
Originally Posted by MANAEUNOS View Post
And I was also always wondering.
First of all why NAs never received a low gas light
The NA was made before the majority of the human race became too stupid to glance at their gauges once in a while.

Quote:
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?
Not a true linear gauge. Also: Shape of gas tank.
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Old 01-10-2014, 01:35 PM   #15
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Quote:
Originally Posted by concealer404 View Post
The NA was made before the majority of the human race became too stupid to glance at their gauges once in a while.
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
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Old 01-10-2014, 01:58 PM   #16
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Quote:
Originally Posted by thenuge26 View Post
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

Become part of the solution, Steve. Become part of the solution.
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Old 01-10-2014, 02:36 PM   #17
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Quote:
Originally Posted by MANAEUNOS View Post
And If the Pump Clicked Off Early, how do I go about it exactly?
(New Pump?)
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
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Old 01-10-2014, 04:35 PM   #18
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Quote:
Originally Posted by triple88a View Post
Consuming oil? Start with a compression test, then move on to the narrowbands.
So I did the compression test
It goes to approx 180-190 in every cylinder according to autozone rental tool
So I assume copression is good
Here is the pic of the plugs


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??

Quote:
Originally Posted by EO2K View Post
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
As far as I know half tank of gas and half test of fumes is the most dangerous mixture
Attached Thumbnails
Very Low Gas Mileage!-tstnkuytwli.jpg  
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Old 01-10-2014, 04:35 PM   #19
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Quote:
Originally Posted by triple88a View Post
Consuming oil? Start with a compression test, then move on to the narrowbands.
So I did the compression test
It goes to approx 180-190 in every cylinder according to autozone rental tool
So I assume copression is good
Here is the pic of the plugs


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??

Quote:
Originally Posted by EO2K View Post
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
As far as I know half tank of gas and half test of fumes is the most dangerous mixture
Attached Thumbnails
Very Low Gas Mileage!-tstnkuytwli.jpg  

Last edited by MANAEUNOS; 01-10-2014 at 05:11 PM. Reason: Posted twice by accident
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Old 01-10-2014, 04:52 PM   #20
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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.
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