Car cuts throttle when hard braknig

[Phloozy]

We have a possible solution! I found a new tuner willing to try and fix it and on the street it seems promising. I will be on track April 24th so I will report back if anything is fixed.

[spidertri]

That's great news, so it was a table in the DME relating the brake pressure to torque reduction?

[Phloozy]

Originally Posted by spidertri

That's great news, so it was a table in the DME relating the brake pressure to torque reduction?

I think so but not sure, the first thing he tried didn't work. Unsure what the 2nd attempt was

[spidertri]

So I had a track day on Tuesday and I did not experience the throttle issue. I was at CMP, which I always had the issue pop up in braking for Turns 1, 8, and 11, but there was no throttle delay for the rev match.

I was so used to it, that when the rev-match happens as expected, I end up braking way too early because I always had to wait until the throttle blip happened. So I was able to brake later and harder and really had to relearn my braking points.

The problem is, I'm not sure specifically what fixed it. I made two changes between the last track day and this one.

1) Installed MILVs and had a StageFP retune done.

Since I had previously used the iFlash tool with Bob and I didn't have a completely stock file, he needed to rebuild my tune file. In this process, my hardware number on my DME tune went from 8613002 to 7602216.

I asked Bob about it and he told me the that 7602216 base file was the most stable MSV80 version in his experience. So, it's possible that this earlier version DME file does not have the throttle cut in it the same way as the later files.


2) I coded the sport brakes option on my car's VO (+SPBR) This changed several parameters in the DSC to different values, including front and rear axle pressure models, oversteer friction coefficients, and yaw compensation. It's possible one of these coded settings affects the brake/throttle interaction, or the brake signal that gets sent to the DME.


I think the easiest way to figure out what changed it is to remove sport brakes from my VO and see if the throttle delay comes back, although I really don't want to because it was so nice to drive the car and have the rev match happen as expected.

[Phloozy]

Originally Posted by spidertri

So I had a track day on Tuesday and I did not experience the throttle issue. I was at CMP, which I always had the issue pop up in braking for Turns 1, 8, and 11, but there was no throttle delay for the rev match.

I was so used to it, that when the rev-match happens as expected, I end up braking way too early because I always had to wait until the throttle blip happened. So I was able to brake later and harder and really had to relearn my braking points.

The problem is, I'm not sure specifically what fixed it. I made two changes between the last track day and this one.

1) Installed MILVs and had a StageFP retune done.

Since I had previously used the iFlash tool with Bob and I didn't have a completely stock file, he needed to rebuild my tune file. In this process, my hardware number on my DME tune went from 8613002 to 7602216.

I asked Bob about it and he told me the that 7602216 base file was the most stable MSV80 version in his experience. So, it's possible that this earlier version DME file does not have the throttle cut in it the same way as the later files.


2) I coded the sport brakes option on my car's VO (+SPBR) This changed several parameters in the DSC to different values, including front and rear axle pressure models, oversteer friction coefficients, and yaw compensation. It's possible one of these coded settings affects the brake/throttle interaction, or the brake signal that gets sent to the DME.


I think the easiest way to figure out what changed it is to remove sport brakes from my VO and see if the throttle delay comes back, although I really don't want to because it was so nice to drive the car and have the rev match happen as expected.

Do it for science! So the tuner I am working with fixed the issue but it was with a janky way of forcing the ECU to never close the TB. While this works it is risky if the valvetronic fails. Sadly I could not test much as it seems i stressed my pressure plate strap and it broke on my 2nd lap at the track monday...... The car was really hard to get into 4th gear on track and then when i rev match downshifted (yay it worked!) the pressure plate broke and I couldn't get into any gear.

[spidertri]

Dang man, that's a rough. Was it your original pressure plate or did you swap it for a new one when you had the engine out?

Yeah, I can do it for science. It's pretty easy to do through Protool so I could probably change it at the track between sessions.

[Phloozy]

Originally Posted by spidertri

Dang man, that's a rough. Was it your original pressure plate or did you swap it for a new one when you had the engine out?

Yeah, I can do it for science. It's pretty easy to do through Protool so I could probably change it at the track between sessions.

No it was the one that came with my clutchmasters fx400.... Bimmerworld says it could have failed from not rev matching so hopefully now that I can rev match it wont be an issue.

[amg6975]

Originally Posted by Phloozy

Do it for science! So the tuner I am working with fixed the issue but it was with a janky way of forcing the ECU to never close the TB. While this works it is risky if the valvetronic fails. Sadly I could not test much as it seems i stressed my pressure plate strap and it broke on my 2nd lap at the track monday...... The car was really hard to get into 4th gear on track and then when i rev match downshifted (yay it worked!) the pressure plate broke and I couldn't get into any gear.

The good news here is we know that my hypothesis of it being a Valvetronic safety net was correct.

I wouldn't worry too much about it honestly, Valvetronic failures are fairly rare, and if it did happen for some reason, you're smart enough to shift to neutral and shut the car off. Maybe just preventatively replace the Valvetronic motor every few years.

But... just knowing that it's the TB closing and not the actual "throttle" value should be helpful in tuners finding where the safety switch is in the software.