ChrisV 02 - Z28

iTrader: (1)

I Atap'd the Z today and was monitoring the L/S Trim. At idle LTRIM was reading +9, and during normal driving conditions it was reading around +15 - +20 range. My STRIM were running -5 to +5. I have CAI, Lid, K&N, MAF Ends,SLP Y-pipe and SLP Loudmouth exhaust. Due to these high flow goodies, is that the reason my ltrims are so high? From info i have seen their numbers were around 8-10 for LTRIM.

Now at partial throttle fuel tuning,
Tune so the LTRIM is near -2 to 0, (not STRIM Correct)

Am I right about this....or not
At partial throttle, normal driving condition the A/F is adjusted by the LTRIMS to adjust injector pulse to achieve the 14.6 constant, but at WOT it uses a look up table for injector pulse. MY question is if I have "+" ltrims in closed loop, will this same avarage value be added to the open loop value therefore making the ratio richer? = not good for power?

Also maybe some kind of fluke but on my atap list i have
Long Term Fuel Trim Bank 1
Long Term Fuel Trim Bank 1
Long Term Fuel Trim Bank 2
Long Term Fuel Trim Bank 2
and
Short Term Fuel Trim Bank 1
Short Term Fuel Trim Bank 1
Short Term Fuel Trim Bank 2
Short Term Fuel Trim Bank 2

Why are they in there twice?
The first of each seem to "Flicker" more during logging and the second of each seem to be more steady. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

Anybody else notice this?

<small>[ November 14, 2002, 10:01 PM: Message edited by: ChrisV 02 - Z28 ]</small>

ChrisV 02 - Z28

iTrader: (1)

If the Short Term Fuel Trims are slightly negative or 0 all the time, why would the LTFT's be so high in the positive range???

JWRENCH

My understanding is the long term is a coarse adjustment and the short term a fine adjustment. For instance when you put your maf ends on, the short terms were probably staying high so the long terms kept bumping up more and more to try to get the short terms to be near zero. Also if your long terms go much higher your gonna see a lean code light pretty soon. You might consider changing your maf back to stock and checking it again just to see what happens. As for the double listing on the atap, Mine has it also and I'm really sure why. Maybe someone else can chime in and explain this better...

JWRENCH

Sorry, I meant I'm NOT really sure why. Welcome aboard by the way... <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

Kevin V 2002 SS

This is ChrisV not Kevin

From reading material i understand the difference in short and long term.

Now is the long term trim also added into WOT fuel levels?

JWRENCH

Welp, looks like it's just you and I on this post Chris. Someone please correct me if I'm wrong but if I remember correctly it will use the long terms only if they are positive numbers while cruising.

Kevin V 2002 SS

Chris and I both adjusted the MAF last night. I need to do some cruising so the computer can adjust and then recheck with Auto Tap and see if it brings the LTFT in line better.

Doc99SS

iTrader: (2)

STFT is the SHORT term fuel trim
LTFT is the LONG term fuel trim.

STFT are updated every millisecond or so.
Once the STFT value is pegged at +25% or -25% for some period of time(I dont know the exact value), the LTFT is adjusted up if STFT is pegged at 25% or adujsted down if STFT is pegged at -25%.

The STFT will constantly move around, you should not even bother to monitor it. It is the LTFT that you need to tune for part throotle operation. If the LTFT value is positive, the PCM is adding more fuel, also a positive LTFT will add fuel in during WOT operation. If the LTFT is negative, the PCM is taking fuel away, however, to protect the engine from a lean condition at WOT, a negative LTFT will not result in fuel being taking away at WOT.

You want to tune the MAF table so that you have the LTFT all below 0%, like between -4% and 0%. If the LTFT is positive, the MAF sensor/table is under-reporting the amount of air going into the engine. So increase the MAF table values to bring the LTFTs down below 0%. You can do this with LS1Edit.

Does this help any?

Kevin V 2002 SS

Yes it does. Thanks!!! How long does it take for the cars computer to "learn" the reprogrammed MAF settings???

Doc99SS

iTrader: (2)

It is my experience that it takes at least 15 minutes of city driving for the PCM to relearn all fuel cells and LTFT values.

You can determine this yourself. Make a noticable change with LS1Edit or MAFT. Go out and drive around, every 5 minutes take a long ATAP session. Record 4 of these and compare them.

Of course, the larger changes you make will require more driving time for the PCM relearn process.