LNF 2.0L E69 "Desired Boost" is limited to 255kPa?

[wilson0x4d]

I've been trying to wrap my head around understanding how "Desired Boost" sensor arrives at the reading that it does.

I went through a number of logs and cannot find a "Desired Boost" value above 255kPa (155kPa+baro), is this just my setup or can others confirm this limit is real?

Why do I care? I can, and do, use PID control to achieve the desired boost profiles that I want. However, I wanted to work on a more stable high-boost profile at WOT by raising Desired Boost (the target) instead of adjusting the PID loop to ramp fast and decay slowly.

So.. before I assume there is a hard limit on Desired Boost I wanted to confirm with other more experienced tuners here.

Thanks

[ECaulk]

255kpa is the limit of what the ecu will see for the TMap sensor (intake manifold map sensor) even if you have the GMStage1 sensors, so thats why it won't ever request anything higher than 255kpa.

[MarkTucker]

Confirmed! 255kpa is just a limit for the read out on the scanner. You can definitely target and hit high boost levels tho.

[califcarm]

See post #18 from Chris at HPtuners.
http://www.hptuners.com/forum/showth...aled-to-300Kpa

I take that to mean that the PCM does not acknowledge anything higher than 255 kpa from that sensor in the intake manifold. Extend that idea and you might interpret that to mean all calculations using it can only use 255 as a max (logical). So if desired boost (and I assume you mean DAL - Desired Air Load?) uses the reading from the Tmap in the intake manifold, then it will never see anything higher than 255kpa, therefore not try to achieve anything higher than that (since it can't "know" if it got there). And I mean it won't try to reach higher than that on it's own, but it seams actual air load is greatly affected by Wastegate duty cycle tables as well, so obviously higher boost is achievable.

If Desired boost (or Desired Air Load I am still assuming you mean) uses the lower tmap in the charge pipe then it does see and read higher and can target them and try to get to them.

I am not sure which sensor it is using so I am not really sure either.

I ended up using DAL values in the high load area of 255kpa (since I assumed it could not read or calculate higher than that) and just fine tuned the WG duty cycle table to get a little higher than 255kpa (was targeting 262-263 kpa in my case which I achieved).

[wilson0x4d]

Just to be clear, when I say "Desired Boost" i'm referring to parameter ID 2360 (commanded/target boost, basically), which is different than physical sensor readings given by Boost[2339] and BoostLowRes[2338].

It sounds reasonable that this is limited in the same way that [2339] is limited (E69 likely only uses 1 byte to store this value.)

As an aside, we've got a Kappa here with an ZZP LDK swap (the LNF died) and with an identical DAL the E69 only demands 18psi boost max. We'll be reprogramming the LDK this weekend to boost correctly, but it looks like DAL is not "absolute pressure" but is instead "airflow%". How to translate this into "Desired Boost" I've no idea (I've tried working out the math using VE and MAF readings to no avail, but this would be nice to know how to calculate manually.)

Regardless, thanks for the confirmations