factry a/f ratio and emissions testing

[luckythirteen13]

first off, hi guys. this is my first time posting here although ive been around cars, especially mustangs for a long time. i recently switched mustang forums since my other forum sort of dried up. too many arguments and not enough knowledgable people.

anyways, i live in california and have strick smog laws. i have a wide band o2 sensor kit for tuning and was wondering what the stock a/f ratio was on the 5.0 mustangs before the cats(1992 to be exact). or a better question, what is the leanest i can tune it to, to make sure i pass. i will have all the smog crap on for the test, although its not on now. ill also be running 8* of timing and a 195* stat. what should my a/f ratio at the tips with the the cats installed? sorry if this has been asked before

thanks guys

 

[90mustangGT]

When cruising/lot throttle/idle on a EFI car, there is no exact number, it cycles between rich and lean very rapidly, this is nessasary for cats to operate properly, it's deeper than that but lets just say to watch for the rich/lean cycling, it should do this at least two times a second.

 

[luckythirteen13]

so would leaning it out, among many other things, do anything for passing or should i just lower the fuel pressure a bit and let the ecu take care of the rest?

 

[90mustangGT]

so would leaning it out, among many other things, do anything for passing or should i just lower the fuel pressure a bit and let the ecu take care of the rest?

No matter what you do to pressures and such, the computer will just compensate by altering the pulse width of the injectors, you can't win. Unless you do something to the computer or trick it, which will not nessasarly make you pass emmisions. Your hydrocarbons would decrease, but NOx would increase, and the cat won't work correctly. The rich/lean cycle keeps the exaust and converter cool, while effectivly burning the Hydrocarbons. Fuel Injection is not like a Carb.

 

[HISSIN50]

I am sure someone else with a wideband will chime in and let you know the A/F stuff (Jason is right about stock NB Lambas cycling between rich and lean, but a WB should provide a real number).

How are you going to tune it (you mentioned tuning it. Do you have a handheld?)?
Like Jason said, the puter will adapt to the FP changes. Also, I would run lower octane fuel but keep the timing up, just a little shy of detonation (that should be clean).

Welcome to SN and good luck.

 

[luckythirteen13]

sounds logical about the FP. ive always heard run low timing and mid grade fuel, bet every once and a while i hear high timing and low fuel. they check my timing during the test and it must be near stock (damn california smog crap). can you explain the reasoning of how timing effects it?
i know what hydrocarbons are( has to do with the ignition right. thats what ive been told) so with full msd ignition i think ill be fine there. what are NOx. i know its on the test but have no idea what it is and what effects the NOx reading

 

[emagdnim]

Pull a plug wire off one of your plugs before the test

 

[jrichker]

Pull a plug wire off one of your plugs before the test

Bad advice unless you were just kidding. It will make the HC emisions go up from the unburned fuel that it will pass out the exhaust.

Advancing the timing increases combustion temps which increase NOx emissions.

 

[luckythirteen13]

thats what i thought. thats why i will be running 8* of timing, the lowest legally allowed.

i think he was kidding