air/fuel ratio - Toyota Nation Forum : Toyota Car and Truck Forums

***MR2Jedi*** · 11-21-2004, 11:28 AM

what is air/ fuel ratio for stock '91 MR2 Turbo? anyone know?

JekylandHyde · 11-21-2004, 08:11 PM

The A/F number changes constantly. It is not a set number.
It will change with the boost, throttle position, rpms ... even with the weather.

toyotaspeed90 · 11-21-2004, 09:41 PM

should be between 14.4:1 and 12:1

JekylandHyde · 11-21-2004, 09:52 PM

At idle, a stock MR2 will be much leaner than 14.4:1 and under boost it will go much richer than 12:1.

toyotaspeed90 · 11-21-2004, 09:53 PM

well, then it's outside of the optimum values and you're probably losing engine efficiency

JekylandHyde · 11-21-2004, 09:57 PM

When cruising/idling the car will go super lean for fuel economy.
There is no load on the enigne, so no risk.

You are correct that going richer than 12:1 is not efficient. Wasting gas and a lot of potential HP ... but it is much safer for the engine and reliability which is what Toyota intended.

toyotaspeed90 · 11-21-2004, 10:00 PM

actually i beg to differ that going any richer than 12:1 is good because it's safe.... granted, currently my aw11 is running richer than that (i don't have correct fuel maps)... but excess gas with time will slowly get into the oil, along with if it's rich enough it can cause the car to buck or stop accelerating, which can be potentially damaging to the internals

JekylandHyde · 11-22-2004, 06:08 AM

Agreed ... any "extreme" can be bad.

The fact is when the ECU detects knock, it will add excess fuel to cool the engine down and clear up the knock. Some amount of excess fuel does make the engine runner safer (but slower) ... but I would agree, that if you have an extreme amount you will have problems as well.