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Discussion Starter #1
Hey forum, it's been awhile.

I have a 02 miata base. When i bought the car about a year ago, I got about 24-26 mpg. Now it seems that I only get 19-22 mpg... I only use high octane (premium) and have tried different gas stations. Maintenance has always been kept up. Tires set accordingly. No CEL.

I have been getting 250 miles to the tank! This is starting to give me ideas about trying a different vehicle...

My question for you guys is, have you been getting bad gas mileage lately? Is it something in the gasoline? Or is this the characteristics of a Miata?

Thanks, curv
 

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O2 sensors are heading south, dirty MAF, low tire pressure, hung caliper?
26-32+ should be normal, depending on how you drive.
 

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Discussion Starter #3
O2 sensors are heading south, dirty MAF, low tire pressure, hung caliper?
26-32+ should be normal, depending on how you drive.
02 sensors I will investigate, but should a CEL be on from those?

MAF? What solution can you use to clean it out?

Hung rear calipers might be an issue. I know my rear calipers are junk when I did the brakes last month. (and yes, I adjusted them to spec.)

Anybody else getting bad gas mileage?
 

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Gas mileage got worse this last week, my guess is they just winterized the fuels up here. Happens every year. I got about 250 miles on my last tank.


Wait you're in FL nevermind lol
 

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Yah. The fuel stations change to different mixtures in the winter in the Rustbelt. Higher ethanol content, IIRC.

The MAF I would clean with an aerosol electronics cleaner found at any autoparts store. Be gentle and judicious.

I am not too familiar with the NBs, but the O2 sensor on my car attributed to a 10-15% decrease in fuel economy as it became older. I've had stuck calipers, too. It was easy to diagnose, the car wouldn't freewheel backwards on a slight incline very easily. Also, after short drives, I got out and touched the wheels. The one rear wheel was considerably warmer than the other.
 

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i thought 250 miles per tank was good???
i get around 250 a tank hmmmmm know its got me thinking.........
 

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I got about 24-25 mpg on my '92 with a roughly dialed in MSPnP on a WBo2.

I recently switched back to the modified stock ecu. I estimate my fuel econ to be around 27-30.

I don't drive the car easy.
 

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I get 250 a tank (that's ~25-26 mpg) on regular 87 and I don't drive conservatively. 22-27 city, 32+ highway seems normal.

Edit: '01 NB2.
 

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I got about 24-25 mpg on my '92 with a roughly dialed in MSPnP on a WBo2.

I recently switched back to the modified stock ecu. I estimate my fuel econ to be around 27-30.

I don't drive the car easy.
On this note, does anyone have an idea as to what AFRs the OEM ECU runs at cruise? I'm sitting at 15.3:1 and I'm curious if I can go any leaner. Getting ~24-25mpg with my DIYPNP right now. Then again, I do idle at 1000rpm and ~14:1, need to retune that.
 

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Discussion Starter #14
I got about 24-25 mpg on my '92 with a roughly dialed in MSPnP on a WBo2.

I recently switched back to the modified stock ecu. I estimate my fuel econ to be around 27-30.

I don't drive the car easy.
Where did you go to get the stock tune for the ecu? I was a dumb dumb and got the recall done for that.

On this note, does anyone have an idea as to what AFRs the OEM ECU runs at cruise? I'm sitting at 15.3:1 and I'm curious if I can go any leaner. Getting ~24-25mpg with my DIYPNP right now. Then again, I do idle at 1000rpm and ~14:1, need to retune that.
good question. I'll need to figure out that info.
 

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Bronto, that is where mine cruises on the regular ECU. I still have the WB, just set it back to factory settings when I removed the MS. Brain might be able help you.

IIRC, I found an AFR table someone posted on MT.N. His was a little leaner for better fuel economy.

OP, there's a little thread drift there...were were talking about standalone ECUs (megasquirt). If you pull the negative connection on your battery, hold down teh brake pedal for 30 seconds, then reconnect, your ECU should go back to default. Go drive it for a little while.
 

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Thread recall was only on the NB2s (mine had it done as well). KFJ has an NA, right?

The recalled ECU tune shouldn't affect your mileage.
 

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Discussion Starter #18
You run 87 Octane on a NB2? Why?

I run premium ever since I bought mine. I would not run the 87 octane due to the VVT with my 02!

But good info coming in. Makes me feel like the car is ok, just gotta throw some parts at it.

STILL, 250 miles to the tank is horrid. Is anybody else having crappy gas mileage? :fp: *poop*
 

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You run 87 Octane on a NB2? Why?
Well, usually, since I'm cheap. Premium is recommended, not required. I've noticed no significant difference in mileage or power switching between 87 and 91 fuel. It's only when I went to a crappy no-name gas station that I've ever had pinging.

I fill up with 89 or 91 when I have any performance driving event, and occasionally for regular driving as well.
 

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I consider 240 is average for my 99 NB1. According to my gas tracker (prior to getting a cluster with a low fuel light) my average per tank is about 22-23. Given it's an older car, all maintenance has been well kept by me. This is all city driving, highway it's around 26-27, maybe more. Most of the time I fill up about 11 gallons of whatever is cheapest.
 
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