After installing new exhausts, my m3 eats gas like cookiemonster eating his cookies

[piloto]

If you are going WOT (or close to) and shifting at lower rpm, you're going to use up more fuel than if you go with less throttle and slightly higher rpm.

Nevertheless, I am assuming that you have changed your driving characteristcs from before when you had the OEM exhaust. It might be to avoid some bassy/boomy sound at low rpm with the new set-up, or conversly that you are going to WOT to try and duplicate such a sound at low rpm. Either way, best bet is to closely analyze your habits, as they are sometimes done so intuitively that we don't notice them ourselves.

Aside from that, as another poster mentioned, it could be something totally urelated to the exhaust itself and maybe could a leak in the fuel system, or something gone haywire with the ECU, although I would doubt this is the case as such problem are extremely uncommon and rare.

[Sean@PYSpeed.com]

^ this!

or just pounding for the sound!

[Seven7]

Originally Posted by Sean05

hmmmm changing exhaust wont see much of a change... you must be revving the sucker a lot... hey cant blame you specially on that exhaust...

i got better results when i went full exhaust.... no primary cats.... and i got a better MPG... so its your driving habits must be the new exhaust made you press that gas more often... LOL

The problem is I havent been doing that LOL. I've been driving very conservatively ever since putting on the exhausts and I havent revved over 4-5k rpm.

[SchnellM3]

Im sooo confused...

OP puts on a new exhaust and doesn't rev the car past the rev the car or see how it sounds

I can't get enough of the exhaust sounds even when it was stock I loved taking it up to red line. That's where they sing the most

[Seven7]

Update - it's been 3 months and the car is still eating a lot of gas. I average 18.5 litre/km in the city and about 12L/KM on the highway. One thing that scares me is that the car consumes more fuel when stopped and idling. It eats 39.5L/Km when I leave the engine on but car parked...Some is wrong. AND NO I DONT FLOOR IT..THATS NOT THE REASON WHY IT EATS MORE GAS. I DRIVE IT FOR A DAY KEEPING THE RPM LOWER THAN 3K AND I STILL NEED TO GET GAS EVERY 2 DAYS. WE HAVE A SERIOUS PROBLEM HERE.

[KJ]

If you enable BMW Efficient Dynamics via coding, it actually tells you to shift at just under 2K rpm for the best efficiency. And that's coming from BMW directly.

I personally don't shift at that low of an RPM because you accelerate too damn slow that way, but technically, it is the RPM to shift at to get the best fuel economy (according to BMW).

[Canuckles]

Originally Posted by Seven7

Update - it's been 3 months and the car is still eating a lot of gas. I average 18.5 litre/km in the city and about 12L/KM on the highway. One thing that scares me is that the car consumes more fuel when stopped and idling. It eats 39.5L/Km when I leave the engine on but car parked...Some is wrong. AND NO I DONT FLOOR IT..THATS NOT THE REASON WHY IT EATS MORE GAS. I DRIVE IT FOR A DAY KEEPING THE RPM LOWER THAN 3K AND I STILL NEED TO GET GAS EVERY 2 DAYS. WE HAVE A SERIOUS PROBLEM HERE.

Idling while stationary theoretically has 0 mpg, seriously though you bought a guzzler what did you expect.

I get around 16.2l/100 with 90%/10% city/highway respectively.

[TurboBimmer]

Originally Posted by Seven7

Update - it's been 3 months and the car is still eating a lot of gas. I average 18.5 litre/km in the city and about 12L/KM on the highway. One thing that scares me is that the car consumes more fuel when stopped and idling. It eats 39.5L/Km when I leave the engine on but car parked...Some is wrong. AND NO I DONT FLOOR IT..THATS NOT THE REASON WHY IT EATS MORE GAS. I DRIVE IT FOR A DAY KEEPING THE RPM LOWER THAN 3K AND I STILL NEED TO GET GAS EVERY 2 DAYS. WE HAVE A SERIOUS PROBLEM HERE.

lol

In fact you're eating WAY more fuel than 39,5l/100km when you car is stationary

Because if the car doesn't move...well...it takes an infinite amount of time to reach that 100 km. And you'll consume an infinite amount of fuel.

But to not scare the crap out of you, BMW usually makes the gauge switch to 0,00 when you're stationary

On a serious note, the M3 is known to be quite a gas guzzler. But you should check your driving habits.

[1sikbmr]

Im way too lazy to actually figure out what the conversion to mpg would be. So i cant help

[Seven7]

Dammit you guys, you guys are missing the point. My point is that after installing my new exhaust, the car started eating gas noticeably more (and it is said that with better exhausts, the car should be even more fuel efficient).

[Singletrack]

Originally Posted by Seven7

Dammit you guys, you guys are missing the point. My point is that after installing my new exhaust, the car started eating gas noticeably more (and it is said that with better exhausts, the car should be even more fuel efficient).

Rear section will make virtually no difference in terms of fuel adjustment.

I wouldn't lug the transmission around under 2k on a regular basis either. Not revving out the engine is actually bad for it - will lead to build up.

[Seven7]

Originally Posted by Singletrack

Rear section will make virtually no difference in terms of fuel adjustment.

I wouldn't lug the transmission around under 2k on a regular basis either. Not revving out the engine is actually bad for it - will lead to build up.

One my buddies told me that there might be a problem between the computer and the exhaust. Something about the computer not being able to pick up the new exhaust system. Is this true? If it is, should I bring it in for service and have them check it out? Maybe reprogram the car in any way?

[Singletrack]

Originally Posted by Seven7

One my buddies told me that there might be a problem between the computer and the exhaust. Something about the computer not being able to pick up the new exhaust system. Is this true? If it is, should I bring it in for service and have them check it out? Maybe reprogram the car in any way?

There might be people living on the moon. I cannot say for certain.

Based on what we know about this engine, there is very little chance that a rear-section-only exhaust is going to have any significant impact on fuel delivery. You can change the entire exhaust out and the programming does a very competent job of adapting.

[Jbook]

Did you try what I mentioned in my previous post on the first page of this thread? Shifting at low RPMs makes the car get worse gas mileage! When cruising on the freeway at 70-75 mph and 3k rpm, my car gets better mpg than if I stay at the same speed in top gear at 2k or 2.5k rpm.

[tibra1]

More air ..more fuel?

I too have noticed this car chomps less gas when you live in the higher RPM range.

[Seven7]

Originally Posted by Jbook

Did you try what I mentioned in my previous post on the first page of this thread? Shifting at low RPMs makes the car get worse gas mileage! When cruising on the freeway at 70-75 mph and 3k rpm, my car gets better mpg than if I stay at the same speed in top gear at 2k or 2.5k rpm.

I did today actually, I shifted my gears at 2.5- 3k rpm and I did 13km (8 miles) in half a quarter tank. Im going to fucking smash my car because this is so fucking frustrating.

[Stealth ///M]

put the stock setup back on.

[Moxie]

Originally Posted by Seven7

Update - it's been 3 months and the car is still eating a lot of gas. I average 18.5 litre/km in the city and about 12L/KM on the highway. One thing that scares me is that the car consumes more fuel when stopped and idling. It eats 39.5L/Km when I leave the engine on but car parked...Some is wrong. AND NO I DONT FLOOR IT..THATS NOT THE REASON WHY IT EATS MORE GAS. I DRIVE IT FOR A DAY KEEPING THE RPM LOWER THAN 3K AND I STILL NEED TO GET GAS EVERY 2 DAYS. WE HAVE A SERIOUS PROBLEM HERE.

Tenderfoot - it's not the exhaust. If you leave the car parked & it doesn't move, you will get 39.5L/KM....because it's not freking moving. F@ck me -

[doc19]

Originally Posted by Seven7

Update - it's been 3 months and the car is still eating a lot of gas. I average 18.5 litre/km in the city and about 12L/KM on the highway. One thing that scares me is that the car consumes more fuel when stopped and idling. It eats 39.5L/Km when I leave the engine on but car parked...Some is wrong. AND NO I DONT FLOOR IT..THATS NOT THE REASON WHY IT EATS MORE GAS. I DRIVE IT FOR A DAY KEEPING THE RPM LOWER THAN 3K AND I STILL NEED TO GET GAS EVERY 2 DAYS. WE HAVE A SERIOUS PROBLEM HERE.

I think you mean 18.5 litre/100km city and 12 litre/100km highway. For us imperialists that is about 13mpg and 19mpg

I don't know seven7, that is about right for the m3. I do mainly highway driving (live and work right off a major highway) and I get about 18.5mpg. What were you getting before?

Unless you really meant 18.5L/km, which is .12mpg. Then you really have a problem.

[Grail05]

OP: i guarantee you that its not the exhaust. replacing the rear will not change your MPG... I have no clue on why your car is eating more gas but here is what i suggest...

1. put the stock back on ... drive as normal work home work home.... until you are at 1/4 or when the warning low fuel comes up... I suggest to wait for the second warning...
2. now when the second warning fuel beeps comes up... check how many total miles you have used on a full tank...
3. do the same on your new exhaust.. if you are really worried this is the only way we can test the car if its really your exhaust but i guarantee you its not your exhaust.


Even with my Akra SLip on and my Full catless and restless i was only loosing about 5-10MPG.... which is not a big difference and no i wasnt tune...

Now when i had my Akra paired with 200 cell and resonator... i was able to get 5-10mpg on a full tank... not sure why or what would cause it but with an Akra 200 cell cat and res works a lot better..

now I have a Slip on AKra with OEM xpipe... I get the same MPG with my OEM exhaust...

FYI: this is just my experience