OK! When I'm looking at the fuel trims, does - (neg) mean I'm running rich or lean? The damn things fluctuate so much, it's hard to get a good reading. I've been told I want +1.56% on my Long Term trims while cruising and 0.00% on them at WOT. Any suggestions on how to set them would be apreciated.
Jim

 

fuel trim is what the computer is doing to compensate for rich or lean running engine. A positive fuel trim the control unit is adding fuel and negitive is taking away. fuel trims are going to fluctuate alot at idle and crusing cause the 02 sensors are going rich/lean continuously to store oxygen in the catalytic converter. You can't set fuel trim you can only affect it. Typically fuel trim + or - 12 is showing an outstanding problem (ie vacuum leak, IAC problem, CTS, bad 02 etc)

 

NEGATIVE FUEL TRIMS IS RICH AND POSITIVE FUEL TRIMS IS LEAN.

 

You can't set them without a custom tune.Playing with the spark and fuel settings doesn't do this. playing with those readings will adjust at wot but that won't help you if your way off for normal driving
How long is your truck running before you monitor your Ltrims?
Mine leveled out at -1.56 at a 70 mhp cruise and always went to zero at wot. I was averaging 15.5-16mpg on 94 octane. w/ 3000 stall/4.10's, 20's etc..
If your readings are way off you will need a custom tune to fix it.

I'd say go for a 20-30 minute drive on the highway, and look at your ltrims than. My fluctuated alittle but all factors of 78= -78, -1.56,-2.34 etc...

 

that is 100% true but the motor really isn't lean or rich anymore, that is what the ltrims are doing is adjusting the a/f ratio till it is perfect, not rich or lean. you want your ltrims to be a little negative most of the time, for some reason when you are negative it puts the ltrims numbers at WOT to 0 and that is where you want them when you are ready to tune your WOT a/f ratio.

if your ltrims are positive the computer will put a positive number at WOT also and it wont always be the same so when you are trying to adjust you WOT fueling the computer will be fighting you. it is kind of hard to explain but you will get it if you keep reading about it. i am told ltrims also effect timing and that slightly negative gives you all the timing you have programed in, not sure if that part is true or not.

bottom line, if you have a programer you want them to be slightly negative, anywhere between 0 and -10 would be fine, if you can keep them 0 and -5 that mgiht even be better, when i had those BIG injectors i the best i could do was between 0 and -12.

 

Well, I guess I'm Ok then. They only fluctuate between +3% and -3% most of the time while crusing around town and do go to 0.00% at WOT. On the freeway crusing at 70 mph, they sit at -1.56 most of the time. Thanks fo rthe help guys .
Jim

 

my long term fuel trim is at +9 constant at idle.. what could be causing this? i saw iac and i was wondering how that could affect iac because i think my iac might be messed up a little

 

anyone?

 

your mods will change the ltrims, headers for sure. if you are doing your own tuning and are shooting for the absolute best you can do then you would want to start by working them to be a little negative, then so some WOT tuning. with just a few mods it isn't really much to worry about. the computer is just reacting to the changes you made to your set up. the computer can go + or -25% so it is just doing it's job right now is all.

 

alright...so i shouldn't worry about...man i wish ls1 edit would work...looks like i need an ls1