[gtmax500]

Hey guys, I know I'll have to get in touch with BMS but I thought I'd make a post here in case anyone else had a similar problem and to get the issue known if I'm the first.

Back story: I attended an HPDE this weekend at Summit Point Motorsports Park (Summit Main) in West Virginia (my 5th HPDE with this car). Currently I have a JB4 installed along with a Fabspeed Sport Cat. I have a few other mods but those are the only engine related mods. The first session of the day after my warm up lap as I'm heading down the main straight I approach 135mph (my top speed since I ordered it with all seasons) and my car throws a drive train malfunction and enters limp mode. I pit out and cycle the ignition and the drive train malfunction goes away so I head back out onto the track. next time around same thing happens. I approach 135 and the DT malfunction appears and I go into limp mode.

I pit and use my OBDII reader because I now have a CEL and I have 3 confirmed codes. The codes are misfires in cylinder 1, 3, 4 and multiple pending codes. I clear the codes and cycle the ignition and everything seems okay. For the rest of the weekend as long as I kept my speed under 120 all was fine. I just picked 120 since it was a decent amount under 135.

on one of my last laps of the weekend I got distracted and forgot to keep my speed under 120 and I enter limp mode again. Luckily I had less than 5 mins left in the session so I just pit out and turned off my car.

Now I'm not 100% sure but I'm fairly certain this problem has something to do with how the JB4 operates when the car hits the top speed limiter. Perhaps when the ECU retards the engine at top speed it changes what signals the JB4 expects or vice versa and things go haywire. Obviously I need to completely remove my JB4 and hit 135mph but that may be difficult off the track.

Anyways, just though I'd make a post here since I haven't seen anything similar around here and perhaps someone has some knowledge on this issue. I appreciate any discussion.

[amw896]

I thought only flashes removed top speed limited and jb4 doesn't have the capability. It seems like it's cutting timing to deal with the factory limit setting.

[bryan_G01]

Only flash DME tunes remove top speed limiter.

Only other way is you meet the car in Germany and recode it under the time/mileage allowed which is next to impossible.

135 mph means your car came with runflats.
155 means you had the performance tires.
Theres specific codes on ur VIN that tell you, but im too lazy to look for them.

JB4 seems like its doing its job, the car has more in it, but the limiter is causing the error. Don't go above 135 and you wont have the problem, or go get flash tuned. That are your options.

This is also same reason I got a flash tune, hitting 135 on front straight with the Dinan s3, ripped it out the next day.

[gtmax500]

Originally Posted by bryan_f22

JB4 seems like its doing its job, the car has more in it, but the limiter is causing the error. Don't go above 135 and you wont have the problem, or go get flash tuned. That are your options.

This is also same reason I got a flash tune, hitting 135 on front straight with the Dinan s3, ripped it out the next day.

I did some more research on the N54tech forums and it looks like yes the JB4 is definitely to blame for these errors. Something about the DME doesn't like having full boost when hitting top speed and the throttle body closing.

IMO this seems like a huge oversight on BMS' part and they should definitely fix this. It's a little silly they cannot make an option to reduce boost as you approach a certain speed. Staying under 135 isn't difficult but its a PITA if you forget and have to waste precious track time to pit out and cycle the ignition.

Anyways, thanks for the responses. Once this thing is out of warranty I am definitely getting a flash tune but until then I'll probably just remove the JB4 next time I'm on the track.

[frenchfry675]

Originally Posted by gtmax500

I did some more research on the N54tech forums and it looks like yes the JB4 is definitely to blame for these errors. Something about the DME doesn't like having full boost when hitting top speed and the throttle body closing.

IMO this seems like a huge oversight on BMS' part and they should definitely fix this. It's a little silly they cannot make an option to reduce boost as you approach a certain speed. Staying under 135 isn't difficult but its a PITA if you forget and have to waste precious track time to pit out and cycle the ignition.

Anyways, thanks for the responses. Once this thing is out of warranty I am definitely getting a flash tune but until then I'll probably just remove the JB4 next time I'm on the track.

I've hit top speed multiple times with jb4 map2 and never had anything happening. Are you hanging at that speed for a extended amount of time? What map are you running?

[wjjkoevoets]

Stock LPFP may be the root cause here. There are reports of it not being able to keep up if you're relatively low on fuel and travel at or near top speed.

[bryan_G01]

Originally Posted by wjjkoevoets

Stock LPFP may be the root cause here. There are reports of it not being able to keep up if you're relatively low on fuel and travel at or near top speed.

It's not a fuel issue. And you have to remember jb4 is used for multiple purposes including meth control to being thrown on a stock car.

Its not difficult to hit 135 and lift to avoid the issue... I don't know what track you are at where you need to be faster for a longer period of time... It will make you better in the esses if you don't wan't a flash tune to fix it.

[wjjkoevoets]

Originally Posted by bryan_f22

It's not a fuel issue. And you have to remember jb4 is used for multiple purposes including meth control to being thrown on a stock car.

Its not difficult to hit 135 and lift to avoid the issue... I don't know what track you are at where you need to be faster for a longer period of time... It will make you better in the esses if you don't wan't a flash tune to fix it.

Sorry, I was thinking of the 155mph limit, not 135mph limit. In which case it can be an LPFP issue.