Boost solenoid at or near 100% duty, boost is still low(ish)

[PeepPaadam]

It's me again with the Porsche 944 Turbo PnP VEMS. I got the stock cycling valve to work but maximum boost I can reach with it is ~0.7 bar. Stock ECU can reach 0.8 bar of boost.

The wastegate has very weak spring from the factory (0.3 bars) and the KLR ECU controls a boost solenoid that has 3 ports. It either lets boost signal to wastegate upper chamber (powered state) or diverts the signal to pre-compressor (unpowered state).

I had to increase boost solenoid duty to nearly 100% to get 0.7 bars of boost, anyone has any ideas what to try next? I am using default 21hz frequency, would changing frequency influence the total openin time? If duty is nearly 100% I could as well just connect the solenoid to GND instead of PWM'ing it and try if it builds more

[fphil]

may be check the logical of the cycling valve versus Vems signal ?

[PeepPaadam]

I just tested by assigning cycling valve pin as rpm output so it just grounds it above 2000 rpm and when fully open the maximum boost is still 0.65 bar. Seems that this is is what the factory intended...

[fphil]

0.7 factory for the biturbo. Is it a kind of SEM valve with pipe restrictions. Better to use a Piersburg/Vems.

[gunni]

Are you sure the stock ecu is running the same ignition as you?
Retarded ignition can and will bump up the boost values without any benefit.

[PeepPaadam]

I have used the stock ignition table (DME "full load" table at stock boost areas).

Yes, it is SEM valve but as I mentioned earlier, the main goal is to get the car using as close to stock ECU as possible, so far none of the ECU's has managed that hah So VEMS has been so far the best. 99% of ECU's require installing separate crank trigger because they cannot utilize 132+1 trigger ont he crank (there is no cam sync).

[fphil]

The SEM valve is of leaking type, and the boost level is set by restrictors in the pipes. The contol of the valve is for overboost or knocking, at least this was the case for my biturbo. Not a matter to put a Piersburg valve in place. It is mostly recommended since the SEM valve gets older in a bad shape.