Hey , I have a s14 sr20det with AVCR, S-AFC II, 300zx MAF. I have bought 550cc injectors and need to know how to tune it. If anybody has any experience with this please let me know.Thanks.-Jon

An SAFC can only change MAFS signals, not injector signals. The only thing that you can try is to turn up the fuel load across the powerband.

SpeedRacer1 wrote:An SAFC can only change MAFS signals, not injector signals. The only thing that you can try is to turn up the fuel load across the powerband.

Uhhh...and how pray-tell do you think the SAFC is used for fuel tuning?

What I suggest is you read the SAFC manual, and do a few searches. In your case, you need to alter two things

1) you need to change the hotwire MAF "in" and "out" numbers to correct for using a Z32 MAF.2) you need a proper method of tuning (such as an EGT gauge, or better yet, a wideband o2) so that you can get the fuel curves correct.

~matt

I believe I'm using hotwire 2in 6out for my Z32 mafs. I have 550cc injectors with a Big28 and my fuel map goes from around -14 at idle to around -8 at 7200rpm at full boost (I think). I have it switch to high throttle map between 70% and 90%, so it's only when I go WOT that it switches to that map. My map is fairly good, I have it idle at like 16.5:1 because I can and on throttle it goes from around 15:1 to 11:1. It's not perfect, but pretty good for just tuning it on the higway by myself while watching the afc and wideband. I need to get on a DYNO soon though.

msaskin wrote:Uhhh...and how pray-tell do you think the SAFC is used for fuel tuning?~matt

The SAFC gets the voltage from the MAFS, then changes that voltage before going to the ECU.

So if you turn up the knob to increase fuel, you are just telling the ECU there is more air than there actually is. Turn it up 50%, it tells the ECU there is 50% more air than is actually flowing through the MAFS. The ECU makes the changes and injects the proper amoung of fuel to the stock injectors. If you change the injectors, the ECU may not send the right signal depending on the size of the injectors.

So you see, the SAFC intercepts MAFS signals before they reach the ECU and changes them. Then the ECU unknowingly dumps more or less fuel in accordance with that newly altered MAFS signal. The SAFC does not tell the ECU how to run newer larger injectors, for that you need a piggyback, standalone, or rechipped ECU. Though you can sometimes use larger injectors that take the same signals.

Yes you guys had a misunderstanding. Msaskin thought you mean you couldn't adjust fuel maps with a s-afc which you can (by faking the air signal as you pointed out). It's not ideal, but it's cheap and it works.

Back to the original topic. I forgot to mention that my numbers might be a lot richer than some. My car ran lean with the stock ECU, don't have numbers but I was running lean and getting 450+ miles/gallon on the highway. So even though the s-afc is leaning out the signal due to the 33% larger injectors, I am also richening it up to correct for how lean my car wa s running.

Technically if you're injectors are 33% larger than you want to fake a signal of -33 across the rpm range, although that only works in theory, not in practice. I ran around -28 across the board when I first installed my s-afc with stock engine/turbo/mafs, and just 550cc's.

Remember you are nt making a real fuel map, you are compensating for changes in an existing map. So you don't neccessarily have to richen the s-afc fuel map up at higher rpms under hi throttle (under boost), because the ecu is already richening up your a/f's. You are just correcting that factor, so if you ran -20 on the s-afc across the board you would still hav a fuel curve that slowly richend as your rpms increased, but you would be faking 20% less air to the ecu. I'm probably not doing a very good job explaining this so you should talk to someone who is a little more knowledgeable with tuning an s-afc.

"Technically if you're injectors are 33% larger than you want to fake a signal of -33 across the rpm range, although that only works in theory, not in practice."

This is what I wanted to know. I know how the safc2 works, I was just wondering if there were any special equations, or ways you could get 550cc injectors to work without dynoing it. I guess I will just have it dyno'd, Thanks unfrgivn and everyone else.-Jon

I've got -30 on boost (approx 3000-7200). We hooked up a wideband the other day and at 15 PSI on my 1820 the A/F ratio was 10.9:1 across the rpm range. -30 for the low throttle map is way too little fuel. The wideband said 17-18:1 at idle and cruise.

hey speedracer...can u tell me the difference in stock KA24E 270cc injectors to CA18DET 370cc injectors (u were talking about signal from ecu to how much fuel is sprayed depending on injectors differences)?? mainly cuz i have the SAFC and will be running approximately 7-9 psi of boost and need to know how to tune the a/f within each rpm range and stuff like that...i dont need a fuel pressure regulator if i have larger fuel pump do i? im asking this part cuz my auto tech teacher at college said i will need a larger regulator...but he works on chevys any input would be great. Thanks

I dont really understand what your asking. What injectors do you plan on using, and on what engine?

Your engine already has a fuel pressure regulator. So I assume you are asking if you want an adjustable.

If you get a larger fuel pump then you may or may not need an adjustable fuel regulator, this depends on the engine though I would say no you dont need a larger one to run 7 to 9 psi of boost. (on an SR)