I bought used Apexi SAFC II on ebay.
MAF ECU and SAFC
On stock car there’s a Mass Airflow Sensor (along with temperature sensor) that outputs pulse output that goes directly into the ECU. Faster pulses mean that more air goes into the intake piping. Slow pulses that little air goes in. So ECU knows at any time how much air goes in and how much it should inject though the injectors (at stock configuration) to make 14.7:1 air/fuel mixture. N0w, when you install bigger injectors OR raise fuel pressure at fuel rail, you mess up things. More fuel gets injected. You need SAFC or similar to step in. You need to fool the ECU 
Cut the signal line between MAF and ECU. Put fuel computer in between that changes the pulse rate. Most cases you need to slow down the pulses to fool ECU thinking it receives less air so it injects fuel for shorter period of time.
OK, now to my problem. I think the SAFC II was sent to me broken. I connected the device to the car’s ECU and tried to start the engine. All i got was backfiring like hell. SAFC was registering Mass Airflow Sensor signal “Kar”. I hooked up my laptop to the ECU with OpenPort 1.3U cable and Evoscan software. I noticed that the ECU registered no air coming in. When i removed the SAFC temporarily, it registered air coming in – ie Mass Airflow Sensor signal was being received.
So i was sure that the SAFC wasn’t outputting anything useful. I took it to my workplace and hooked its input to frequency generator with 50Hz square wave. Output to oscilloscope and got this:
Here is link to SAFC II configuring instructions: Link
SAFC Karman sensor output.
Output transistor Q4 needed to be replaced.
Schematics .. kind of