[csu87]

So was trying to get some baseline runs before some bigger mods are done and had some issues on the dyno (graph below) this dyno has done numerous 335xis in the past with no issue as well.

DSC off (button held until the symbol popped up)

During every pull, car would be fine up to about 4k rpm, then a small jolt and power dropped dramatically as seen on the dyno. We did a couple runs and every time same thing. Watched what the dyno was seeing tq wise between front and rear wheels and 40:60 rear biased until that 4k rpm. Then the rear would drop out, then front would drop out, then it would go back to fairly normal.

Anyone had this happen before? Shop thinks maybe the center diff is going out? Or something else? No one there had any idea. Couldnt find any codes either using the bmwhat app. Want to take to dealer but not sure how to explain to them without mentioning the dyno incase they try to deny warranty based on that as well.

[Aashenfox]

Tire sizes?

[csu87]

ive driven over 10k miles on these tires with no issues. and are stock runflats

[shadow191]

The printout shows they used a Dyno Dynamics and those aren't mechanically coupled so if you get a big enough differential between front and rear speeds, your power could cut out. Not sure why it would happen at the same rpm each time though. Or it's detecting slip and transferring power as it should. If it's happening at the same rpm, that seems more like an electrical glitch vs. your diff failing. Maybe their dyno is doing something at 4k rpm which causes the car to think there is slip.

What you're experiencing is something that AWD guys worry about on the dyno - not just BMW, but if you google it, there's debate about which dyno is best. I think the only AWD dyno that is actually mechanically coupled is the Mustang. Not that other dynos don't work, but you're relying on software to ensure the drums are in sync and sometimes that can go wrong.

[csu87]

Im going to go to another shop with a mustang dyno to see if it does the same thing or if it dynos normally. Hoping it is just the dyno, but it is weird that they have done other 335xi's with no issue. a guy with an xi was at the shop watching and he never had this issue. His was an 08 though and maybe between the 08 and 09 there is a difference in how the car reacts?

[Senpai]

Originally Posted by csu87

Im going to go to another shop with a mustang dyno to see if it does the same thing or if it dynos normally. Hoping it is just the dyno, but it is weird that they have done other 335xi's with no issue. a guy with an xi was at the shop watching and he never had this issue. His was an 08 though and maybe between the 08 and 09 there is a difference in how the car reacts?

I have an 09 and was dyno tuned with no issues. It was a mustang dyno though.

[csu87]

Yeah ive been on a Mustang Dyno in the past with no issues as well.

[gtaccord]

I have successfully had my car on a dyno dynamics but the shop owner said that it was extremely difficult to setup correctly for awd.

I feel like your differential issue is actually a dyno issue. Go find a mustang or dynojet.

[kamfa39]

Never had issue, all dyno on mustang dyno