A rom tune absolutely negates the need for a SAFC. A tune sets up the calibration to properly use the Z32 MAF and the injector size being used. If you're combining a tune with a SAFC, you're doing it wrong.
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Originally Posted by SRSmith
To my surprise, I'm running lean. So I immediately shut it off and set it to -5%. I'm still a bit lean even with the cold start, so I set it to +10%. Now I'm running around 12.5 afr, but as it warms up the motor creeps into lean territory again.
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The ECU has cold temperature enrichment tables, so make sure the engine is fully warmed up before you "tune" that SAFC. What do you consider lean here also? Are you running 12.5 at idle or full boost? You should be seeing stoic (14.7) at idle when the engine is warmed up, 12.5 at warm idle is dumb rich.
Quote:
Originally Posted by SRSmith
I've found a couple FC for good prices. However, I'm stumped by this SAFC so i doubt I'll do better with a Power FC.
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Your setup isn't that complicated, normal Z32 MAF with S15 injectors. You can email Martin an RSEnthalpy and he can most likely sort out a tune for you easily. Would be WORLDS better than trying to screw around with a SAFC like it's 2001 all over again.
Here's some more technical info on why that SAFC should be trashed: With larger injectors, you need to reduce the injector pulse width to deliver the same amount of fuel. The ECU uses something called a load scale table to help determine a pulse width at a given RPM/load combo. Load is primarily determined by the MAF reading. There's a bunch of math involved and other factors, but I'm keeping it simple here.
These are made up numbers to show the theory/point here:
At 4500 rpm and a load of 100 (full throttle) the ecu will command a pulse width of 20 to deliver a certain amount of full.
Now, with larger injectors a pulse width of 20 will inject too much fuel. What you really need is a pulse width of 15 to deliver the same amount of fuel as the factory injectors.
The SAFC will change the MAF reading so that at full throttle at 4500 rpm, the ECU will "see" a load of 75 and command a pulse width of 15.
Okay, your fueling is "correct" but here's where the whole thing falls apart: the ECU uses a load scale for a bunch of other things, including (as pointed out already) timing tables. At a given RPM, timing can be 3-7 degrees advanced when going down from 100 to 75 on the load scale. So at 4500 rpm and a load of 100, timing is 12*, but at a load of 75, timing is 18*.
Plus, you're now not even using the last cells in the tables that are indexed to load because that SAFC is tricking the ECU to only ever see a max load of 75. So you took a 16x16 table and limited it to 16x12. Effectively losing granularity and control in the ECU.
A proper rom tune (or standalone) will adjust the math on the ECU itself so that your MAF reading reflects an accurate load value and injector pulse widths are calculated correctly, accross the full table size. Once the ECU is calibrated correctly to your setup, any outside modifiers (aka SAFC) are not needed and will interfere with proper operation.