What's the purpose of teh fuel trim readings?

[NoGood]

Anybody know?

[NoGood]

Anyone...?

[trularin]

Don't know what teh is, but fuel trim is a term used to describe the ECM's ability to maintain a Stoichiometric condition in the engine.

[NoGood]

"teh" is the.

[NoGood]

Originally posted by trularin


Don't know what teh is, but fuel trim is a term used to describe the ECM's ability to maintain a Stoichiometric condition in the engine.

So what do it's readings indicate?

[John S Peterson]

Fuel trim in numbers is the addition or subtraction of fuel as required to maintain as close to 14.7:1 as possible. You have both short term and long term corrections that will allow the cat to work as efficiently as possible. OBD II's only job in a nut shell is to protect the CAT so in a sense every OBD II vehicle has it's own 5 gas analyzer on board. Pretty cool if you think about it.

[Thorin]

John,

Would you post some pictures of you Rambler restoration in your Member Gallery?

Thanks

thorin

[Rick Parker]

Fuel trim can be controlled with your right foot.




Rick

[427sharpe]

Fuel trim is the reading thru the pcm/ecm for the % of air-to-fuel. In diag terms, it can tell you if the O2 sensors are working, and if they are 'lazy', which can cause driveability problems and trigger a mil. Can also help find contaminated MAF, dirty intake, leaking injectors or a ecm fault.

[John S Peterson]

If you had an air fuel sensor (wide band) you could use Lambda calculations to really tell what was going on with AFR, but unfortunately very few vehicles at this time other than european vehicles use them. OBD II uses an O2 sensor monitor that checks response time as well as checking the heater circuit which will trigger the MIL. Any fuel trim numbers out of the norm for any length of time will usually turn the MIL on and if emissions exceed 1.5 times the Federal Test Procedure the light will flash indicating extreem danger to the CAT. If anyone is interested I have a lambda calculator that you can just plug your 4 or 5 gas readings into to get what your REAL AFR is, this is great for tuning you just have to have your gas readings to use it.

[John S Peterson]

Thorin....I will get some pics together...it's been an interesting project so far and right now I'm just about finished with the body work, so now the fun begins

John