Jrp1978

iTrader: (10)

I was driving home the other night and for no reason my long term fuel trims went to -12.50 and stay there unless i let out or hammer it... they where around -1.56 to 0 . I always have my predetor pluged in so i watch it close. ( Oh at 65 mph)
I had the car dyno tuned with predetor software and the guy told me not to mess with injector slopes at all , but that is the only way i can get the long term trims back up , but i dont want to **** anything up doing that .

With the trims like that the o2 still fluctuate normaly. Anywhere from 40 mv to 880mv ----unless i am in wot and they are stuck at about 935 mv

I guess i would like to know what happen. The car really doesnt seem to run any different exept for the way it idles. Drops between 900 and 500 for quite a will before stablizing!
I am really tired of ******* with this car so tired of this and that every damn time it rains my o2 sensors go nuts .
But hey this is all my luck !

Country Boy

iTrader: (24)

If the O2s go crazy when it rains, look at the wiring. Its probably burnt through and shorting when it rain. I had that problem once.

Frost

iTrader: (45)

-12ish isn't ideal, but it's better than +12. If you modify your injector tables you will inadvertedly modify your WOT fueling also. If you paid for a dyno tune to tweak your WOT I'd imagine you don't want to screw that up. Just let it be at -12, your other issues are most certainly secondary.

Jrp1978

iTrader: (10)

what is short and long term anyway
is it just for econmy

Country Boy

iTrader: (24)

short is what the pcm has to do right then and there on the fly and long term is more of an average over time.

Jrp1978

iTrader: (10)

OK so lets talk 02 for a minute ........ Mine are reading any where from 40 mv to 830 mv and when in wot they read about 890 to 900 is this normal ? Why do they drop so low is that part of the deal .

Frost

iTrader: (45)

the up/down swing is closed loop control acting on your fueling to try and maintain an avg AFR of about 14.7:1. At WOT the car fuels open loop and richens up (PE) which is why they stay high.

RedWS6 00

The occilation of the O2 sensors when not in WOT is good. The computer is constantly adjusting fueling to be around 14.7AFR. if you have a wideband guage you will see your AFR swing from something like 14.1AFR to 15.1AFR. The fuel trims are adjkusting this. If it finds a cell that its too right then the fuel trims will take fuel away.
So for come reason your car thinks its running 12% richer than needed, could it be faulty wiring, who knows.... perhasp the VE isn't tuned only WOT.

The other thing to take note of when entering WOT although your fuel trims wont adjust in this mode but dosn't it use the last Fuel Trim value as a modifier for your WOT fueling? if this is right you may be running leaner at WOT, however your O2's are saying 935mV you could be any AFR below 14 AFR.

You may just need to tune the VE Table.

txhorns281

iTrader: (12)

Only when the last trim value is a lean condition

Maf = tune maf table
Sd = tune VE table

Frost

iTrader: (45)

I'm a fan of this method of tuning as well.... well sorta

I personally like to get the VE near perfect under 2K and really close between 2 and 3K. From there all measured AFR % error goes against the MAF. In no time at all you'll be hitting the commanded number in PE.

txhorns281

iTrader: (12)

That's how you get tuning done accurately and quickly! I remember back in the day, I used to tune the whole VE up to like 5K!!! lol Makes sense if you plan to run SD mode, but I've since come to the realization that spending the majority of your time on what the PCM will actually be referencing, gets you great results plus avoids lengthy tuning sessions.