E89 Z4 INOAS boost ceiling with MHD Question

[Osiris]

First I've heard of any issues with the Z4 boosting on any ROM. Certainly not a common issue as I've worked on a few Z4s and they usually boost better than the 335i.

I've had a custom tune on my Z4 for the last 7 years. It originally came with IGD0S, I then updated to IMC0S and had to re-tune again and finally INA0S came out around 2013 and that needed a new XDF building a map working out for that too. Never once has an issue with boost being limited.

Best thing to do is read through the whole thread so you have a bit more info to work with in the understanding of this. Not sure if you have already as its allot to read through I know but everything is explained pretty well. Maybe you will pick something up that we didn't ?

 

[carabuser]

I can say with complete certainty that there is no boost ceiling that would limit to 14PSI on any ROM.

Also the differences between the Z4 and 335i ROMs are slight. The big differences are low pressure fuel regulation and power steering. There's also some differences relating to the wheel sizes and also changes to the fuel injection calibration for the 35is map. Boost control is the same though.

 

[Osiris]

I can say with complete certainty that there is no boost ceiling that would limit to 14PSI on any ROM.

Also the differences between the Z4 and 335i ROMs are slight. The big differences are low pressure fuel regulation and power steering. There's also some differences relating to the wheel sizes and also changes to the fuel injection calibration for the 35is map. Boost control is the same though.

So interestingly enough we are dealing with the same issue again with the car, we have been since last year without even knowing it I have been trying to get more power out of the car, a bit more boost and we have been unable to get the boost past 21PSI. I mean we have gotten it to spike to 24 - 26 here and there but its for an extremely brief moment! where it quickly goes back down to 21psi and tapers down to 16psi. it's doing exactly what it was doing with MHD just with a slightly higher ceiling.

My Tuner and I have gone back to last year going through so many logs to see if the load target has ever been higher than 175 and it has NEVER gone higher. In the last week he has adjusted the load a little more each time getting me to log and send the log but no matter what he changes the load target to in the tune the car wont go above 175 load target and 21Psi boost. We have load target set to 200, Boost ceiling set to 1.5bar and Boost limit Multiplier set to 3. on any other N54 this would have you boosting 28 - 30PSI. yet my car wont budge.

I don't understand this weird behavior, My Tuner is now opting to start from scratch and see if he has missed something. Hopefully he can figure this issue out as its very strange indeed!

@carabuser you sound like a very knowledgeable guy so if you have any insight on what could be causing this please let me know as right now I am at a loss.

 

[carabuser]

So interestingly enough we are dealing with the same issue again with the car, we have been since last year without even knowing it I have been trying to get more power out of the car, a bit more boost and we have been unable to get the boost past 21PSI. I mean we have gotten it to spike to 24 - 26 here and there but its for an extremely brief moment! where it quickly goes back down to 21psi and tapers down to 16psi. it's doing exactly what it was doing with MHD just with a slightly higher ceiling.

My Tuner and I have gone back to last year going through so many logs to see if the load target has ever been higher than 175 and it has NEVER gone higher. In the last week he has adjusted the load a little more each time getting me to log and send the log but no matter what he changes the load target to in the tune the car wont go above 175 load target and 21Psi boost. We have load target set to 200, Boost ceiling set to 1.5bar and Boost limit Multiplier set to 3. on any other N54 this would have you boosting 28 - 30PSI. yet my car wont budge.

I don't understand this weird behavior, My Tuner is now opting to start from scratch and see if he has missed something. Hopefully he can figure this issue out as its very strange indeed!

@carabuser you sound like a very knowledgeable guy so if you have any insight on what could be causing this please let me know as right now I am at a loss.

Without seeing the binary it's hard to say.

In quite basic terms the load target is actually a load ceiling. This is the maximum cylinder fill the driver can request. The load target is a proportion of torque request and load ceiling, so a 50% torque request from the pedal would equate to half the value in the load ceiling at that RPM. The load target in the XDF is actually the load ceiling.

How much boost the DME will target is a function of a lot of factors. It takes the load target as a starting value then uses some logic that takes into consideration the VANOS position, calculated exhaust pressure, ambient pressure and temp and also the current target boost pressure, hence why you sometimes see the boost target slowly creep up.

If the load req param in your logs shows a value of 200 and you are seeing a boost target of 21PSI then that's higher than I'd expect. At 200 load it should target about 18PSI. If your tuner is messing with the MAP scaling then that's going to mess with the load actual you're seeing. When using MAP scaling MHD will automatically re-scale the boost in your logs so be the true value but the DME is still seeing the fake scaled value so it will only report a low actual load value.

You have no real choice other than to stay with MAP scaling if you want to target above 21.5PSI. If I ever get around to upgraded turbos I think I'd start looking at manipulating the actual load value in DME to match the true boost reading, that way everything stays in check.

 

[Osiris]

Without seeing the binary it's hard to say.

In quite basic terms the load target is actually a load ceiling. This is the maximum cylinder fill the driver can request. The load target is a proportion of torque request and load ceiling, so a 50% torque request from the pedal would equate to half the value in the load ceiling at that RPM. The load target in the XDF is actually the load ceiling.

How much boost the DME will target is a function of a lot of factors. It takes the load target as a starting value then uses some logic that takes into consideration the VANOS position, calculated exhaust pressure, ambient pressure and temp and also the current target boost pressure, hence why you sometimes see the boost target slowly creep up.

If the load req param in your logs shows a value of 200 and you are seeing a boost target of 21PSI then that's higher than I'd expect. At 200 load it should target about 18PSI. If your tuner is messing with the MAP scaling then that's going to mess with the load actual you're seeing. When using MAP scaling MHD will automatically re-scale the boost in your logs so be the true value but the DME is still seeing the fake scaled value so it will only report a low actual load value.

You have no real choice other than to stay with MAP scaling if you want to target above 21.5PSI. If I ever get around to upgraded turbos I think I'd start looking at manipulating the actual load value in DME to match the true boost reading, that way everything stays in check.

Thanks for the detailed response. Very much appreciate the time taken to write that all out so thank to you for that

One thing though is that the map is currently set to 200 load target. The car is only showing a load Request of 170 - 175 no matter what he does. We would like it to be 200 but that just isn’t happening unfortunately.

This is the first time he is seeing a car behave like this. :/ I will relay this information to him though.

 

[carabuser]

Looking at the logic it would seem that the load target will be restricted by a calculated pressure value before the turbo. If you are using MAP scaling then that's probably why. Your tuner sounds completely useless if he's been struggling with that for a year.

 

[Osiris]

Looking at the logic it would seem that the load target will be restricted by a calculated pressure value before the turbo. If you are using MAP scaling then that's probably why. Your tuner sounds completely useless if he's been struggling with that for a year.

Oh ok cool this is very useful info, thank you.

Na the problem is we never knew this was an issue till recently when I asked to up the boost. We have been sticking to roughly 18 - 21Psi up till now. So the problem never showed itself. I am very much on the safer side of things with the car when it comes to tuning. I never go balls to the wall. But since sorting the methanol system out to where it is today with Port methanol and charge pipe methanol and all the other upgrades and maintenance items etc and the much larger intercooler I decided it was time to push the car a little further.