Fuel Tuning - what data to use?

[rsnyderjr2]

Hi Brian - I can use your advice here...

I bought PCMScan primarily for fuel tuning - I have a fuel tuner installed, and an LC-1 and larger injectors that I will be installing soon on my V6 Hyundai Tiburon.  Meanwhile, I thought I would adjust my current setup's closed loop tune according to my LTFT's...

LTFT1 (-12.5%)
LTFT2 (-13.3%)
LTFT3 (-52.3%)
LTFT4 (-51.6%)

(and of course there's a similar difference between my STFT 1/2 vs. 3/4 values as well)

I'm guessing that I should base my settings on the Banks 1 and 2 values    (and therefore pull about 10% fuel across the board in closed loop?) - please share your thoughts when you have time - the advice will be MUCH appreciated!!

Thanks Brian

[BrianP]

Usually when you see fuel trim values for sensors 3 and 4 (either referring to banks 3 and 4, or the downstream after catalyst sensors) then the fuel trims are pretty bogus anyways. Since most vehicles don't have banks 3 and 4, or the catalyst has already altered the air/fuel mixture and the fuel trim value cannot be trusted anymore. So definitely don't go off of those fuel trims for anything.

I would also not use the short term fuel trims for tuning. I would want to wait until the short term trims affect the long term trims, which gives you a better idea of the tuning needs. So, using the long term fuel trims, I would set up a map using the classic dashboard that closely resembles the fuel tables in your engines computer. Then data log the fuel trims until you get pretty good coverage across all the cells of your map. Of course, the cells in the corners will be very hard to fill. Then you can use that map to help guide you through the changes to the engine computer.

I hope this helps!

[rsnyderjr2]

^^ Exactly what I needed to know - Thanks Bro!!

So then yes, I will use the LTFT's 1 and 2 for my closed loop tune, and then use my Air/Fuel ratios against RPM's at WOT for my open loop after the long term trims are settled in...

Oh, and btw, I did finally find the "getting started" info. I was asking about - it's under the Help menu (duh!) 

Thanks Again Brian

[rat]

Keep in mind this may not apply directly to your specific vehicle, i tune my 2000 v6 s10.  I run different injectors, manifold, camshaft, etc.

I would only use upstream o2 sensors, banks 1 and 2 if you have them.

Also, i personaly use both long term, and short term fuel trims, and i average them all together to make my decision as to where i need more or less fuel in the fuel map.

I don't know how your engine determines air flow, or what you have control over.  I would not just add or subtract 10% from the entire map though.  You may be rich or lean in certiain conditions, but at other conditions you may be the oposite.

Also, remember if your engine uses narrow band oxygen sensors your fuel trims are NOT valid for wide open throttle conditions.  You need some sort of wideband o2 sensor(prefferably before the catylitic converter) to know what is going on at wot.

The average that i use in terms of the fuel trims is this:  average=((long term 1 + short term 1)+(long term 2+ short term 2))/2
Leave the negatives in there.  If you are looking at 1 bank it could be possible to have +3ltft, and a -6stft, therefore you would actualy need to take 3% out of it.  This is because the long terms don't update nearly as fast as the short terms.  The computer is constantly trying to force the short terms to 0, and the long terms to a constant.

Only using the long terms is way way too slow.  The short terms update much faster, and you will be able to tune the transients.

Remember this is for part throttle only.

I personaly have an excell spreadsheet that i made to do all of this work for me.  It also goes and categorizes it according to rpm and vacuum.  Then it puts it all in a table that i can multiply against my ve table.  My truck uses speed density as i got rid of the maf.  If your car uses a maf you would sort according to that to figure out where you are rich, and where you are lean.

[rsnyderjr2]

^^ great stuff - thanks Rat!!!

[BrianP]

Don't forget to use the custom Javascript parameters to help do some of these calculations for you.