too lean

[jonk00000]

on my logger, my low fuel trim is 139%. If i try to richen at all, at idle, it will stall any suggestions ?? thanks jon

 

[timloomis]

im having the same problem,but i havent reset my ecu either.that could be the problem,as it goes back to 100% when the ecu resets.and from what i understand,139% means you need to lean it out.

 

[steve]

from what i understand, 139% means you need to lean it out.

That would be wrong. On a 1G numbers over 100% mean the ECU is adding fuel based on the O2 feedback reading leaner than expected.

Steve

 

[timloomis]

so its like a backwards reading?so i'd need to add fuel for 139 and take away for less than 100?

 

[Ghost1984]

so its like a backwards reading?so i'd need to add fuel for 139 and take away for less than 100?

yes if it is over 100 then it means its too lean, 100% is perfect on a 1g, my low trim right now is 102 but my mids and hi are around 88 and 91.

 

[v8s_are_slow]

i usually try and keep my trims around 110%.

but i've had the problem when trying to tune to where they'd hit 139% and stay there. reset the ecu and start off with it rich. slowly lean it out till ya get it around 100%. for some odd reason, sometimes it seems to wanna lock at 139% and stay there awhile if i'm running it too lean. resetting the ecu solves it. or......look at your O2 trims. if they cycle around 100 or less, just keep it there. those trims should eventually come down. it's taken me 2 or 3 days for it to move sometimes though.

 

[timloomis]

mine are finally starting to go down.my o2 trim was all over the place,now it hits 100 or above rarely.ill give it a day or 2 and see what happens.

 

[jazzyjay]

So what is the optimal fuel trim you would want to see at low, mid and high. I need perameters

 

[v8s_are_slow]

well 100% on a 1g is said to be the "optimal" trim numbers. but i prefer running a lil bit leaner than that. around 110-115% in every trim. but it all depends on what your knock and timing numbers are looking like as well. obviously if your timing gets pulled or ya start getting knock, you wanna richen it up. it's also been said that ya don't wanna be going over 10 counts of knock, but to tune for 0. if i remember correctly, 18-20 would be the best numbers to see for timing but don't wanna go under 15.

 

[timloomis]

mine are sitting at 101-117 now.i notice a difference in power too.

 

[steve]

Keep in mind that the trims are only used while the car is running closed loop.

Because of the feedback from the O2 sensor in closed loop, the ECU is adding or subtracting fuel to reach the same AFR as it would at 100% trims.

It's once the car goes open loop that having the car tuned lean (trims over 100%) has any impact on AFR. You can accomplish the same thing by tuning to get trims to 100% while in closed loop and tuning the car with a wideband in open loop to get the best power. DSMlink or EPROM coding makes this easier than with SAFC or MAFT because you don't have to fudge the transition from closed to open loop.

Steve