high fuel trims.

[shay4g63]

Okay I'm SO confused. i've read and read but i'm confused as hell. maybe someone will have a sight the will simplify it for my brain.

My 1g has fuel trims of HIGH-139 Mid-121Low-109

My mods are

2g mas*hacked*
fic 650cc
20g
fmic
6 bolt rebuild block with 157psi compression accross the board
running 16psi
safc2
datalogger

th-postion= low-30 high-80

1k-+6
2K-+4
3k-+2
3.6K-0
4k- -3
5k- -6
5.5k- -3
6k-0
7k- +3


I have a LC1+ kit coming in wednesday so this will help me tune LOTS more. but I"m hoping someone with the same mods MIGHT be out there and help me set a little closer.

 

[viprez586]

Dont worry so much about you're fuel trims. Tune with your wideband once you get it hooked up, otherwise tune off of O2 sensor voltage. Your fuel trims will never be happy with OEM fuel tables.

And honestly, if the car runs good - who cares what your fuel trims are at!?

 

[shay4g63]

i just thought the closer to 100% they are they better

 

[galantlvr34]

You have a boost controller right since you are running 16 psi.I dont see anything about it up on the top.

 

[viprez586]

True, but if your Air fuel ratio is good then you don't need to worry.

Fuel trims are adjusted according to what the global fuel table is set at...which is stupid rich factory wise.

What fuel pump are you running? Is it re-wired?

 

[jtmcinder]

...otherwise tune off of O2 sensor voltage...

No. Just, no.

 

[steve]

Fuel trims are adjusted according to what the global fuel table is set at...which is stupid rich factory wise.

Not quite. The fuel trims are only used and updated in closed loop on a DSM which means they are how much the ECU had to adjust to hit 14.7:1 based on the feedback from the O2 sensor switching.

 

[viprez586]

No. Just, no.

Well that was informative.
The OP clearly needs to do some tuning, starting off looking at the voltage while tuning is a small step in tuning. Combined with looking at knock, and timing - it is a primitive way to get his car dialed in to an extent.

Not quite. The fuel trims are only used and updated in closed loop on a DSM which means they are how much the ECU had to adjust to hit 14.7:1 based on the feedback from the O2 sensor switching.

Thanks for clearing this up Steve. This further reiterates what I meant to say by fuel trims not being a good means of tuning - especially for WOT and when you start modifying things from an OE aspect.


In the end OP all you need to do is get your wideband installed, watch your Air/fuel ratios, timing, and knock. Tuning for zero knock with the leanest AFR will net you the best gains.

 

[jtmcinder]

Well that was informative.

There are plenty of threads on why you should never tune a car using the output from a narrow-band. It doesn't need to be rehashed here. I'm sorry that I didn't put the dots close enough.

 

[viprez586]

I ain't madatcha.

I agree, though...narrowbands are so inaccurate to begin with.

 

[Calan]

I agree, though...narrowbands are so inaccurate to begin with.

Technically, you shouldn't really use the term "accuracy" at all when talking about a narrowband O2 sensor, since they aren't measuring anything in the first place. They are simply switching outputs around a preset voltage that represents a stoich AFR for gasoline and air (14.7:1). Although the switched voltage does represent an instantaneous true AFR (in theory), it only covers a very narrow range; hence the name. And they function very well at what they are designed to do.

This further reiterates what I meant to say by fuel trims not being a good means of tuning - especially for WOT

Well... by definition fuel trims CAN'T be used for tuning at WOT.

You're kind of talking apples and oranges here though. For the best all around performance, both open and closed loop should be tuned. That means using a wideband for open loop so you can actually measure AFRs over a wide range of values, and calibrating reported airflow for minimum fuel trim error during closed loop operation.