I have a bit of a tuning question for you guys.

I have an 00vi swapped 4th gen, running all 5th gen components, including the injectors at stock fuel pressure.


I've pretty much got tuning down for WOT, but I am wondering about partial throttle/low RPM light load tuning when the car is in closed loop. In addition to my wideband I also have an OBD2 scanner, and the thing I was wondering about is my fuel trims.My OBD2 software picks up 4 long term fuel trim banks and 4 short term ones. Of the longterm, only two actually pick up any readings and are at about positive 5 percent. The short term ones though, all 4 banks have readings. The first two aren't trimmed as much, maybe around positive 5 percent, the second two are more around positive 15-20 percent at idle. So here is what I am wondering:


1.) How is it that all four have active readings if the car only has two banks and two o2 sensors?

2.) I have an Apexi VAFC2 that is not pulling or adding fuel right now, it is zeroed out across the board. Should I partial throttle tune it to get the fuel trims as close to zero as possible during open loop?

3.) Why are my fuel trims trimming so much, it looks like it is adding a lot of fuel? In theory shouldn't they be negative since the DEK injectors flow so much more fuel? At idle if I go positive 40 or something on the vafc and add a **** ton of fuel, then I will see the short term trims go negative.

 

I wouldn't even think about LFTF's, especially with a 4th gen ECU.


I would only care about what your AFR is @ WOT and part throttle. If they're horribly off, (in the 10's or 17+) you probably have other problems.

I have my secondary sensors plugged into my primary ports (A33B, different configuration) and everything is fine @ WOT and part throttle (everything as in AFR).

There is no need to 'tune' part throttle with light mods and a functional ECU. Especially with 'only' an AFC.

My LTFT's are all wacked out due to my Z33 injectors. According to my MPG readout, it tells me I'm getting 12-15% better MPG, but I know it's false because my FT's are off.

 

Ok, thanks man, that definitely eases my mind a bit. When you say "light mods" does that include the larger DEK injectors? As long as I tune it so AFR's are around 12.7-13 across the board at WOT and around 14.7 in closed loop/partial throttle I should be good to go?

 

Sounds like you're good to go. Light mods meaning nothing out of control like a full engine build or heavy boost, but heck, even then it should be good. I was actually referring to the point where you would go to a stand alone. That's the only case I'd think about tuning part throttle.

 

Interesting thread!

I also have a 00VI 4th gen,290cc DEK's with wideband and VAFC2. The ECU below 3000rpm is worthless tuning, he does his own thing keeping everything around 15.0-14,7:1 in closed loop. Go for a tuned WOT 13.0:1 AFR with 47psi fuel pressure. Im opening the VI at 4700rpm personally. The stock ECU in non-cel condition shoots 11's:1 around 6000. My VAFC2 removes 5% from 4000rpm in wide-throttle. Im get around 13's:1 by the time I get a look at it (It's in the cigar lighter hole.)

Consider getting that JWT ECU revving 7200rpm. One got around lately in the 4th gen's.

Get that thread rollin'
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