[firecat]

Yeah, I can vary my consumption as well, although 23mpg was lowest I could get in the city lol. Absolute highest one was 3.44mpg (screenshot for reference).

I was trying to point out that his difference in fuel consumption is something that caught my attention as well in the past and I traced it to S+ and D3 for absolute same driving conditions (weather, traffic, trip length etc.).

[dungitowelding]

Im in Prague, Czech republic.

Today was again crazy, morning drive - slow, valve closed, 9l/100km - then afternoon, valve open 16l/km. Im travelling tomorrow around 800km so I will see how it goes

Originally Posted by firecat

From my own experience with a stock G80 is that 4L/100 difference usually comes from having the car in Sport+ and Drive Logic 3.

Same road, same weather, same type of driving, same traffic conditions. Efficient and D1 is 15L/100, Sport+ and D3 is 19-20L/100.

If traffic conditions are going nuts, you’ll see an exponential increase in consumption due to all the stop and go. Same if you drive for less than 10-15KM (sometimes I see 35L/100 if I drive for 1.5KM lol). If I drive like a maniac, oh well… I don’t look at fuel consumption.

I also use OMV MaxMotion 100+ btw. Out of curiosity, what country are you based in?

[PLife]

Winter gas has more ethanol and preservatives. Plus i would definitely press gas more after exhaust too.

[M4ord]

Do you have the ability to read the engine codes through the ODB port? If the car is running rich (fuel to air mix) then you would see these codes and have more information.

[dungitowelding]

I do not have ability to read the codes when the car is running.

I will get back to this after we install intake and JB4. Then I will give it a try for 2 weeks and we will see

[W288SH]

Originally Posted by dungitowelding

Hello guys, I have 24 M3 xdrive, 1.500km, we changed the exhaust, now Remus, springs, spacers, front grill. But - now the car takes 19l/100km it used to be 15l/100km. Anybody had same issue?
I drive the same road, same speed. Thank you.

I noticed a significant increase in fuel consumption after having an aftermarket cat back installed. My theory is that I am accelerating harder and using lower gears so that I can hear it.

[vrships]

This is not normal. 30% increase in fuel consumption should not be remotely caused by any of these mods.

First you probably need a more accurate MPG measurement. Do it on a fixed segment of road , long enough and you can maintain decent and nearly constant speed. Say 80kph on a 2km tour, with minimal acceleration or braking, use the trip computer "individual" to do the average MPG. Repeat it on a different setting (valve closed, sport+, etc) and measure again.

If everything is good, you are supposed to have better flow efficiency both intake side and exhaust side, maybe very little, but definitely in the good direction. Plus the car always adjusts fuel injection instantly based on actual incoming o2 so it does not waste more fuel than necessary. If you maintain similar acceleration on the road, and similar speed coasting, the car overall consumes the same power to overcome the friction and drag, but at a slightly higher efficiency, so your fuel consumption should be slightly lower if different at all. Unless now you are accelerating faster from the stop and pulls harder ? I guess you are not.

The only thing that messes up the above mechanism is if you have bad O2 sensors, so ECU got the wrong numbers of A/F mixture and mistakenly uses more fuel? But your exhaust work shouldn't have touched those and O2 sensor anomalies usually throw errors.

Since you say opening the valve made it worse, do you think the valve works correctly? Does it sound OK? Could it be the valve are actually closed even tighter than OEM and pits a huge restriction on the exhaust and messed up the efficiency?

Others things you can do is run the car WOT, any single gear, see the torque/power gauge shoots up and reaches claimed values as expected? It'd be better if you tested this before the mods.

Or you can do 0-60 full power runs and see if the car performs as it should. With 4wd and LC, 0-100 should be no worse than 3.4s with good grip, and no worse than 3.8s if launched in 2nd gear.

[vrships]

Originally Posted by dungitowelding

Im in Prague, Czech republic.

Today was again crazy, morning drive - slow, valve closed, 9l/100km - then afternoon, valve open 16l/km. Im travelling tomorrow around 800km so I will see how it goes

One more point is this s58 power train efficiency really sensitive to the oil/coolant temp. I can feel the car has almost doubled fuel consumption from a cold start and it gradually goes normal as oil temp > 70C. Could it be the runs you monitored had the cars fully warmed up and still very cold?

From my personal experience, stock car consumption almost doesnt change if it's efficient or sport plus, valve closed or open, as long as I adjust the pedal so it speeds up similarly and maintain the same speed.

[mirob]

WTF is MPG?

[mike@x-ph.com]

Originally Posted by mirob

WTF is MPG?

[SwankPeRFection]

Should have bought a Romulus exhaust instead…. You’d have gained MPGs then. 🤪

[dungitowelding]

So I got the jb4 and Mishimoto intake. The M3 is real beast now. And as I told you before - there is something wrong with valves. Do you guys know how to fix this issue - screen from jb4.

Thank you.

[SwankPeRFection]

Are you sure the valves are hooked up right and actually move when you push the exhaust button? Have you actually had someone look to see they both function properly on both sides? Was this tested before you left the installer? The DME will want to control them itself based on several conditions and not being able to could play some role in this. Check that they’re plugged in and no wires cut or anything. You’d get 2 other codes if that was the case with actuation faults, but who knows. Try clearing codes and then see if anything comes back.

[vrships]

Originally Posted by dungitowelding

So I got the jb4 and Mishimoto intake. The M3 is real beast now. And as I told you before - there is something wrong with valves. Do you guys know how to fix this issue - screen from jb4.

Thank you.Attachment 3651052

So my guess is correct?

How does the valve actually look from the backside? You should see it physically open-half-open-closed in different modes/settings. And it definitely sounds different when you rev it.

Either it is a bad connector/cable, or the actuator is faulty. See if the exhaust seller can help.

[dungitowelding]

Good morning, so I deleted the errors from JB4 and they are gone. Im coming to car guy next week - just to inspect if all is really ok with the exhaust. I will keep it for next 2 weeks and then we will change it back to stock exhaust to see how it behaves.
What I can tell about the mods we have done in general - that Remus exhaust is really loud. It resonates on low rpm on highway. JB4 - did not expect that big impact on the car - it is really great. Mishimoto intake - great choice. Pagid brake pads - low dust, lot of squeaks in slow speeds but it brakes much better then stock.

[SwankPeRFection]

It’s not hard to see if the valves function or not, you can easily look and test this yourself.