Just picked up this 02 MCS a few weeks ago, has about 98k on the clock, did a tune up the second day I had it, air filter and such. Factory wheels and tires set at door jam recommendation 38 psi. All OE Mini parts, I realigned the car myself at work. I drive the car an average of 13-14 miles one way to work, about 80% of that commute is highway! I drive VERY gingerly on this vehicle, I am used to more power so I have no reason to beat on it or flog it seeking a thrill lol.


Ughhh done with my rambling, lets move onto numbers and figures!

I have filled up 4 times within one thousand miles! (800-900 miles)

Most recent numbers I have are, within filling up to a full tank (via gauge) I am getting about 27-35 miles PER QUARTER TANK! No leaks, no CEL, no misfiring! The car seems to have decent power (all the power its ever gonna have), it is COMPLETELY BONE STOCK, no modifications whatsoever!

I am averaging about 100-130 miles per half tank and about 200-250 miles PER FULL TANK! This is absolutely horrid! My stroked, forged turbo Miata with cage, and standalone engine management was getting 30-33mpg highway and about 25-27 mixed! With just a tick over 300whp!

Since I am new to Minis, I am posting here to see if I can get some "heads up" or "tips/pointers" to look for on this vehicle, or maybe there are common problem areas I have not yet learned of and maybe some veteran Mini owners can provide input? I have read something about maybe a leaky bypass valve. Any symptoms other then possibly shitty MPG to look for with that scenario? At light tip-in on the throttle I can hear a slight whistling sound that I attributed to just an intake "sucking" sound though, similar to vehicles with CAI. Am I wrong for this assumption?

 

The only maintenance I have yet to perform is new O2 sensors, but from my deep experience with engine tuning there is NO way a "warn out/aged" O2 sensor can cause a 10mpg+ drop WITHOUT setting some sort of CEL for misfires/too rich/too lean or catalyst efficiency codes. I do believe that fresh O2 sensors would help, but not improve 10mpg+!

 

Well being that you have an 02 the whistling sound would prolly be the super charger..as for the crap gas milage, i'm now facing the same issue..before i busted my oil pan i was getting roughly 25-30 mpg mixed about 430 miles per full tank, now im pushing 275 miles per full tank and i have no clue why either i'm assuming it's my by-pass valve due to the increase in the "yo-yo" sound i now hear..i've only had my 04 mcs for about a year and i haven't run into any major issues until now with my gas milage

 

So what is your calculated MPG? I have gone 60 miles on my reserve, so that works out to a 16% difference with my mileage. Therefore miles per tank can vary depending on how seriously you take the red light.

I think I recall that most r53 drivers report somewhere between 24 to 27mpg. My average (R50 driven normally) is 29 on winter fuel, 33 on summer. My commute is twice your length, but city / highway breakdown is the same.

Two things that seem to make a difference is fuel quality (and of course octane), and a working pre-cat o2 sensor (although a bad one will usually set off a MIL). I'd imagine that a Miata cuts a smaller hole in the wind (lower C/D), and is probably significantly lighter. Factor in that the Chrysler based powerplant of the 1st gen MINI carries with it Chrysler's heritage of lackluster economy. You may just have a normal R53.

 

Hmm .. interesting.

I have an '02 MCS and I can get about 320 - per tank usually averaging 34.5mpg (trip computer spec).

MPG is variable dependent. roof rack? stuck brakes? fuel quality?

I don't recall ever putting 38psi on my tires, but then my 215/45R17's aren't listed on the door jamb sticker. I keep them at 35psi all around for comfort.

 

430 or 330? I've never broken 400 miles on a tank, even when I was getting 34mpg last summer.

Boost - I agree with you about an o2 that bad almost having to set off a CEL. When my pre cat sensor went, I got 23mpg for that tankful, which at the time was a 10mpg drop. But it happened all of a sudden, and I realized it from the code stored which I retrieved after seeing the light. I'm wondering if the pre-cat and post cat sensors degraded similarly, if the ECU might not catch it? Probably a dumb idea, but I've had worse.

 

Well with a fair assumption from filling up multiple times in 800 miles of driving 80% highway, I would guess an R53 fuel tank is roughly 12-13 gallons? SO take that number just as a ballpark measurement and give it benefit of the doubt on miles per tank well say 260 since thats the best ive seen. Thats 21.6 mpg on 12 gallon tank, running the needle all the way down to the bottom of the red dot! Regardless, not very fuel efficient and seems VERY out of place for this vehicle which is not an aggressive setup nor aggressively driven. My Miata MPG numbers were with SPIRITED driving on normal occasion and, seeing full boost multiple times per day. I am going to look into getting a hold of the Mynes tuning kit for this car and simply have it tuned by my dyno tuner just for gas mileage purposes. I dont have a wideband in the car but I imagine this thing is SUPER CONSERVATIVE in fuel trims at WOT, guessing like 9.9-10.5 afr range?

 

My experience with diagnosis of CEL in my profession I have seen double the amount of post-cat O2s go bad as pre-cat sensors, but that could be purely coincidence. I was just shocked that out of a 12-13 gallon tank I was squeezing only a puny 25-35miles out of a quarter tank! Holy SUV!

 

Could be a leaking injector(s)

could be a bypass valve

could be worn out engine (do a compression and leakdown test?)

could be carbon buildup on the valves (more common on second gen cars, but...)

could be a leaky or cracked intake manifold

could be a slipping serpentine belt or bad tensioner

could be brakes dragging (you'd think you'd smell it tho - or see the smoke)

could be electronics gremlins in the ecu (again, you'd think it would set a code)

Have you checked for stored codes?

My old R53 used to do 24 - 28, only on long trips would I ever see 30, and only under 70 mph.

Around town it would do as low as 20-21, especially in the summer with the A/C on and the winter when it got really cold and they changed the gasoline.

 

I forgot what the OBDII code was that lead me to replace my pre-cat sensor. I do recall when I searched it here, the consensus was the pre cat. I wanted to buy both, but the supplier I used only had one in stock. Since my mileage was corrected and no further code was registered, I lost interest in changing the second. BTW, a couple of threads here on that. People strongly suggest going with the OEM, rather than a Bosch or something. I bought an NTK that someone had cross referenced. It was under $90 from an Amazon seller.

As far as calculating MPG, the only method I'm comfortable with is to fill the tank till it shuts off, drive (the more the better, I recommend emptying the tank), then refill until it shuts off, preferably at the same station and pump. Then divide the number of miles traveled by the number of gallons pumped. If your tire diameter is not stock, correct for the difference or use GPS. By the way, I always seem to fill between 11 and a bit over 12 gallons myself.

 

Questions answered.

 

Just did an ECU reset, we shall see how that works out. For me this procedure is pretty "gimmicky/cheesy" but OBD2 interfaces are MUCH more picky and choosy, so who knows its a free check and guess.

 

Perhaps if you check your fuel milage it will turn out to be ok. I have one vehicle where the first gallon takes the guage from full to half tank...actual mpg is 21, tank is 16 gallon.

 

Well in fair defense of the vehicle, I have not taken it to COMPLETELY empty (as in running out of petrol). I have though, ran it all the way to the bottom of the red light needle before, assuming I was on fumes. Could gauge accuracy be THAT far off?!?!

 

When I took my trip up to Salem Mass, I filled up got on the road but drove like a grandma the whole time...doing between 65-70 mph the total trip ended up being about 415 miles...got to my buddies house with 8 miles till empty needless to say i pushed it kinda close but I just wanted to see how far I could really go. If I was driving like i usually do I know for sure I would have had to stop to refill along the way

 

Ahh a fellow PS owner. Pictures of your car please sir?!?! Looking for a good muse to base some modifications off of

(sorry for getting off topic)

 

Boost,

I have a 2003 MCS with JCW injectors, an intake, exhaust, and quick tune from WMW. I fill up when I hit a 1/4 tank every time and always with 93 octane. I put 10.170 gallons in this morning after 295 miles, so I'm right at 29 mpg and that seems to be about my average. My in-car readout says I am averaging 34 mpg, so there is a discrepancy there. I drive on 55mph (60-70mph) country roads 20 miles to and from work, and the rest is city driving. Odometer reading is just upwards of 98000 miles.

The way you list your mpg figures is confusing to me because I have always just checked my odometer reading from one fill-up to the next and divide that by the gallons reading on the pump.

I hope this info, while not a solution, helps you figure out what is wrong.

 

I am using miles traveled (odometer) vs reading on fuel level gauge. So basically 200-260 miles PER TANK miles traveled. And what seems to be 27-35 miles PER 1/4 TANK. So basically, I fill it up (fuel level full mark). Drive till needle hits 3/4 FULL TANK mark, look at odometer and I usually get between 27-35 MILES per that 1/4 tank I just drank down. Also, from full tank to empty tank (per fuel level gauge) I am getting 200-260 miles out of a FULL TANK OF FUEL. My 02 MCS does not have an MPG counter.

 

You really do need to check your milage.

 

i will post some soon Boost...waiting on spacers to come in so i can get her sitting pretty for the summer time...also plan to get the black trim all color matched wrapped in viynal

 

I shall note "fuel added" on next fill up and divide mileage via this number, but regardless this vehicle with soft driving should easily be capable of 27-28mpg range even with a grossly inefficient superchager/intercooler/intake setup.

 

Keep me posted! any pix of it right now? Looking to see stance of vmaxx on these cars in my color!

 

Go to the gas station and fill up.

Reset your trip gauge to 000. (or write down your odometer reading)

Drive for 3/4 tank.

Go to a gas station. Record reading on your trip gauge. (or write down your new odometer reading)

Fill up with fuel again. Get a receipt or write down the Gallons number you bought.


Grab a calculator and do the following:

trip gauge/gallons bought = actual miles per gallon


If you were not using the trip gauge do the following:

new odometer reading - old odometer reading = # miles

then use that number and...

# miles/gallons bought = actual miles per gallon

 

none since i put the vmaxx on...if you're looking into vmaxx you will need to run spacers unless you're going with aftermarket wheels where you can select a different offset..i need to get new rear tires i messed up ordering my front ones so the aspect ratio is off and right now it looks like im running 15's in the front and 16's in the back oh well lesson learned

 

Let us know what the hand calc comes out to. Your short commute is not condusive to fantastic MPG's. How about hand calc on a long trip....