Question about tuning

[Bratvold]

:help:

I have Predator which James has done some custom tuning for.

I have simple mods. FTRA, Lid & K&N, 160 t-stat, and Loudmouth.

Even when I was running the stock tune I would get +13 +14 LTFTs, but no knock.

James has tuned it so it has stock timing and now during idle it's -4-5 LTFT and during part throttle its +3 +5 and WOT it's locks around +8+9.

My after cat O2s get into the mid to upper 800s and my before cat O2s get into the low 900s

I have just recently just changed the fuel filter since I thought maybe I was getting very low O2 values at WOT (60-75) because of it. It seems like that was the case.

Can someone explain to me how spark advancement affects performance and that the optimal setting for this is and how does the PE work @ WOT.

One last thing...everyone says LTFTs should lock @ 0 during WOT, but even the stock was @ +14. What gives with that.

Thanks.

[JandJsTA]

Originally posted by Bratvold
:help:

I have Predator which James has done some custom tuning for.

I have simple mods. FTRA, Lid & K&N, 160 t-stat, and Loudmouth.

Even when I was running the stock tune I would get +13 +14 LTFTs, but no knock.

James has tuned it so it has stock timing and now during idle it's -4-5 LTFT and during part throttle its +3 +5 and WOT it's locks around +8+9.

My after cat O2s get into the mid to upper 800s and my before cat O2s get into the low 900s

I have just recently just changed the fuel filter since I thought maybe I was getting very low O2 values at WOT (60-75) because of it. It seems like that was the case.

Can someone explain to me how spark advancement affects performance and that the optimal setting for this is and how does the PE work @ WOT.

One last thing...everyone says LTFTs should lock @ 0 during WOT, but even the stock was @ +14. What gives with that.

Thanks.

For spark advance in place of me typing it all out try this explanation here under POWER & TIMING http://auto.howstuffworks.com/ignition-system1.htm .... as for optimum setting (spark advance) that will depend on each vehicle, setup and year.. 01-02s timing is generally 2-3º lower then earlier years say @ 26-28º as an avg number at WOT but again it will depend on your setup.

As for PE at Wot... PE is an A/F mode that the PCM uses when it goes to into open loop (WOT) and has it's own fuel map that the PCM uses to maintain an optimum A/F ratio. Good reading here http://www.vetteguru.com/mods/howto/#trims

As for your LTFTs ... if they are not freezing at 0 and stay + when you enter WOT/PE then you are adding that much more fuel to your PE A/F settings thus making it very hard to get your optimum HP A/F setup at WOT. If you log LTFTs as your drive in cruise you will notice that they fluctuate around so you will never know with any certainty where you are with the + numbers each time you hit WOT. So take these out of the equation and make sure they are o or slightly negative at cruise and they will always be 0 at WOT/PE :)

[smiley]

:werd:

if you ltrims are negative or 0 when you enter pe - they will lock in at 0. if they are positive when you enter pe - they will lock in at that current value.

positive ltrims means the pcm is correting for a lean condition by adding more fuel. as posted above - they are not updated during pe. so if the pcm thinks you are running lean - it's going to continue to add that same amount of fuel during pe because too lean = bad things.

that is why the general consensus is to make all your ltrims slightly negative. this is also why you need a scanner with logging capability. looking at live data is slightly better than guessing. just because you think most of your ltrims are negative - doesn't mean they are. if oyu had a log file you could go right to the spot where it switches and see that this is happening :cool:

idle is not a big deal unless you are getting surging or hunting for idle or problems like that. looks like james is getting you close - ltrims from around +13 now down to +3 or +8.... little more tweaking is needed. make sure to do an idle relearn and give the pcm time to relearn everything after a new tune.

good luck!