packetninja

Has anyone else noticed that if the sport differential is placed into dynamic mode vs auto/comfort that MPG drops significantly? If I'm on the highway in D with cruise control on and switch to dynamic on the differential there's usually at least 4-5 MPG drop.

I'm curious what it's doing for MPG to drop that much.

packetninja

Does anyone know what the sound is that comes from under the car every time you open the drivers door? I've read some stuff about fuel pump noises but wasn't specific to b9.

JohnEnglish

Because the transmission shifts later to keep the revs higher and it doesn't shift into overdrive so yeah it's obviously going to hit your MPG. This is all explained in the manual.

You mean the electronic parking brake engaging? Again, it's in the manual.

packetninja

I don't have the parking brake set unless you're saying that the parking brake automatically sets and releases itself when you open/close the door? I don't see any mention of a feature like this in the manual but maybe I missed it.

packetninja

Quotes got messed up, other part of reply -

I'm not referring to putting the whole car in dynamic. If I have the car in individual with everything set to comfort except the sport differential set to dynamic, mpg decreases. This doesn't result in the revs being any higher.

packetninja

Possible that I'm just not noticing higher revs since I tested it on highway with cruise control set.

xtreme571

What mileage are you getting on the highway vs local? I'm clocking in at ~23 on the highway, and about ~18 local, being in Dynamic and S.

I did a long 600 mile drive and got about 28mpg.

superswiss

That would be extremely strange if the sport differential in dynamic mode would cause a 4-5 mpg drop, especially going in a straight line. The hydraulics operating the clutches do use some power, but the effect on fuel mileage is minuscule. Where do you see this drop? Have you actually calculated your real world mpg by keeping track of the mileage and how much fuel you fill and seen a 4-5 mpg drop? Or are you just going off the board computer? If the latter, what number are you looking at? Trip average, lifetime average or current mpg?

FWIW, I drive my RS5 with sport differential in dynamic and everything else in auto mode most of the time. My lifetime mpg is slightly higher than what I managed in my previous B7 S4, which didn't have the sport differential and made less power, but was still a naturally aspirated V8.

I would recommend you drive with the sport diff in comfort or auto for a whole tank and write down the miles, and then do the same with the sport diff in dynamic. Then calculate the mpg you got both times. Don't rely on the board computer. If they are off much, provided you did the same kind of driving both times, then there is something wrong with it.

For reference, here is what Audi said when the sport diff came out for the first time and I quote:
Source: https://www.audiworld.com/articles/q...ism-redefined/

jb606

That's normal, the ECU is just running the low pressure fuel pump to prime the system.

markcincinnati

The sound, I think you're referring to comes from the seat.

The S4 seats, as you know, are massaging seats. The design of these seats includes some rather prominent side bolsters. When you get out of the car, the bolster (left on the driver's side, right on the passenger side) deflates a bit to allow easier egress.

When you open the front door the sound is the bolster re-inflating.

If I read that you don't typically set the "parking" brake, I would urge you to consider doing so. It is, of course, not a requirement to do so, but you may find the stress on the transmission in P will be diminished.