titaneum_grey

I just had my plugs and wires replaced and the fuel injection system run through with cleaner. Before that I was getting about 184 miles to the tank full, roughly 14 miles to the gallon. This is my second 04 8 and I have always gotten the same mileage with both of them,,, till now. After I got the car back I noticed I am now getting only 162 miles to the tank full, roughly 12 miles to the gallon. I am currently on my third tankfull since the job and all three have been the same. I took it back to the dealer tech that did the work and had him look at it. He hooked it up to his PC and found nothing wrong in any diagnostic program. The engine is running great but I don’t understand the decrease in mileage all of a sudden. I know there is an answer to this but I’m not going to get it from the dealer tech. I’m hoping to find it here. Any suggestions?

Mazurfer

Fuel leak?

I'm assuming if you had bad coils that the dealer tech would've picked up on that.
Dirty MAF or anything else that would making you run really rich could be a cause as well........just not sure..............still thinking.

I sure you will find that most people will get about what I am getting and that more like 240+ miles to the tank or 18-20mpg.

titaneum_grey

bad coils would give me a CEL, we checked the fuel mix and it is good. I have changed the Air filter sinve they didn't have one available when the job was done but the one we took out was actually pretty clean.
I keep up on my 8's, but I drive em. I only get the mileage you get when I'm on the highway, and then only when I keep it under 4 grand. thanks for getting back to me. I apreciate the input. let me know if you think of anything elce

PeteInLongBeach

Catalytic converter...

Krazed_Rx8

iTrader: (5)

I cant understand how you guys can manage to get so many miles per tank...

MTspeeds1

I would do a complete tune-up. Then check the catalytic converter. I recently put in a drop-in K&N air filter and I was getting like 10 mpg until it got used to the new fuel to air ratio. Now Im getting 16

Mazurfer

I don't think it's the CAT this time, but I'm sure I might be proven wrong.

alz0rz

iTrader: (41)

I struggle to get anything over 13mpg on any given tank. Been the same on the two RX8's I've owned. I also know many people who get more or less the same. There are us, then there are the people that claim to get 20mpg. Rest assured, you aren't alone. So long as you know your ignition, cat, air intake, etc is healthy, not much you can do.

the only time I can get anything CLOSE to 220-240 miles to the tank is 100% highway driving. this car's mpg in the city is terrible.

alz0rz

iTrader: (41)

And bad coils won't necessarily give you a CEL. You only get a CEL if you misfire, and even then it only blinks.

i would check your fuel trims and see where your LT and ST fuel trims are at..

glassetcher

Got 18 to 19mpg summer and 17 to 18 winter on first motor. Getting about 1 to 2 mpg less on my second motor so far.... Usually about 70% highway driving.

swoope

iTrader: (5)

drive in the city?

beers

Charles R. Hill

iTrader: (7)

No matter how aggressively I may drive, I get 16 city/23 highway and have ever since Day One. I have 60,000 miles since my rebuild (but I used Mazda's pre-cut side seals rather than the custom-gapping I now do) and 110,000 on my housings. Lord knows how low my compression may be these days.

The tech merely plugged into the OBD port and that may not tell you what the problem could be. I typically tell people to start with things that cost no money to service; clean the air filter, wipe off the ESS, reset the ESS profile, clean the MAF sensor, etc.

After that, check the compression.

dieselsdad

I had the same mileage issue when my coils were going out. Was getting 17-18 in town and 20 on the highway, once coil went kaput dropped to 14 everywhere.

As the coils went out, they took the cat with them. The coils brought back almost all of my mileage and a new "used" cat brought back the rest.

dieselsdad

By the way, new coils were BHR units so I don't have to go through this mess again.

nycgps

iTrader: (1)

For some reason, all the "wonderful mpg" story came from everywhere, just NOT New York City ~~~

sucks

Razz1

measuring Miles per tankful is invalid.

Conditions like yours have been addressed through
New coils
CAT
Fuel pump
Each car is different and unique.

Main thing is how you drive and where.

Yould shouldn't get less than 14.5 MPG in the city. AND that's not winter driving where you have to warm up your car.

titaneum_grey

I would like to thank every one for there input. I have since found one of my secondary coils was bad and I have replaced it. Milage actually went down right off the bat but after a few tankfulls and a few mid-range highway runs the MPG seems to be getting back to normal. I'm thinking the engine managment system needed time to adjust after installing the coil.
In the past I had my primary coils go, each at a different time, but both of them did manage to trigger a CEL. So when that didn't happen this time it kinda through me off, plus the drop in power is signifficantly less when the secondary coil went, almost not even noticable till U fix it.
anyways, thank U to all.

Angelo

ZOOM-I-DO

Secondary coil? Where are they located? or is that a part of the main and only coil I know of. Please tell me I've got to know. lol

titaneum_grey

not to wory. the coils are all in one place. as it was explained to me; the 8 has two plugs for each rotor, a primary and secondary. they ignight at different times in the cycle. hence being called primary and secondary. your 8 has 2 rotors which means it has 4 plugs. each pug has it's own coil. there are 4 coils in a row. they sit (from front to back) primry#1, secondaery#1, primary#2 and then secondary#2. U can have one go bad and thus only need to replace one particular coil.

Charles R. Hill

iTrader: (7)

They are called "leading" and "trailing" coils but you have the basic premise correct.

ZOOM-I-DO

Thanks, I was unaware that the 2nd plug-coil combo on each rotor was called a secondary. I replaced my coils, plugs, wires when I purchased the car March '09 (7K miles on them). I'm wondering if I may have a bad (new) secondary coil as my mileage is as bad as yours and only a 4port automatic (90% city). Will take them off and measure the resistance.

Charles R. Hill

iTrader: (7)

Beware that Mazda's specs for determining the condition of ignition coils is such that even failed coils can pass inspection. White marks underneath are non-conclusive, too. The general consensus seems to be that the OEM coils fail around 25K-30K miles.

ZOOM-I-DO

Thanks Charles, I only have 7K on the new ones.
Thought maybe got a bad one, etc..

Will measure looking for big differences.
How much for your (BHR) coil setup?

titaneum_grey

Wow, I've been doing it the old fasion way; pulling the plug wire off and seeing if I get a spark jumping the gap.

mr_a2z05

i used to have the same problem but it turned out to be the coils AND the cat. i had them replaced and it fixed the whole MPG problem and a power loss problem it had.