rb20 maf, odd problem

[Kansei240sx]

Story :

I've worked on several RB20's and 25's including my own and i know the wiring harnesses and engines themselves inside out, but i've never come across this problem before.

A friend of mine has an RB20 that i put a GT32, tomei poncams 256?, JUN intake manifold, 440cc deatschwerks inj, megan FPR and a Z32 maf with a stock ECU.

The thing is, he has an SafcII ( Which i dont condone ). Anyways, the SAFC-II is in place untill he can afford NISTUNE for his RB20 which im going to install and tune.

I wired up the Z32 maf properly 100 percent sure. When i first got it running, i forgot to calibrate the Z32 maf into the SAFC to in 2 out 4.

So we drove the car around and it drove perfectly, pulled smooth, etc... As soon as i calibrated the Z32 MAF in 2 out 4, it felt the same low down, but as soon as i applied load to the engine it cut out and surged like crazy, afr's all over the place and i cant make it to 3000 rpms. We've tried different MAF's, AND different ECU's, tried different grounds.

With the setting In 1 out 1, the car drives awesome, and pulls great... heres a data log of what i recorded a very laggy and unresponsive wastegate at 3 psi d!ck around with the SAFC. I have it at around 11.5-12.1 AFR

I know this post is a little scattered, my bad i've been up for quite a few days ... hours* I'm probably missing something obvious here, but it hasnt slapped me in the face yet.

The values on the chart you see are at the end of the graph, and the dips after each gear in arf's are the vented SARD R2D2 bov.

[mattblancarte]

This is exactly why I didn't tune my own engine.

[wawazat8402]

Im not sure whats going on, but the way Ive always thought of the SAFCs place with a non-stock maf is that its a translator. If you put a Z32 maf on the car and then use the SAFC to convert the signal, is this not the exact same thing as having a stock maf? Ive always thought you should use the size of the injector to help offset the additional airflow at a given voltage. This way you dont have to use the SAFC to do near as much compensation for the injectors or the MAF.

Does this logic sound right to anyone else but me?

[Kansei240sx]

Thats more or less correct. Basically, the ECU sends out a 12 volt signal and When incoming air passes by the MAF sensor, the sensor then sends a voltage signal onto the ECM and applied to a VQ map and assigns a numerical value to the voltage. That numerical value is multiplied by the k value in a mathematical formula to find the proper pulse width needed for a proper AFR at any engine load and rpm.

So.... ECU 12 volt terminal > wire > MAF housing > hotwire > maf signal wire 0-5 volts > SAFC IN > SAFC > SAFC OUT > ECU Maf pin.

The SAFC modifies the MAF's signal so that the ECU gets a different numberical VQ map variable, so the ECU calulates and changes timing and other various outputs.