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...heading for 500+ RWHP
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Discussion Starter #1 (Edited)
Sorry in advance for the long post.....I just need to give all the info I know....

The fuel cut rpm is under the Emissions control systems section of the Haynes repair manual. It states that if you increase the engine speed to at least 2500 rpm, then abruptly release the throttle the fuel injectors will momentarily cut out at 1200rpm and then resume operation an instant later.

First : does anyone know the reason for this?

Second : I have an apex turbo timer (pen type) and I like to leave it on the A/F ratio display. Under normal driving conditions it reads and average of 14.5 which is about where it should be. BUT.... and time I am crusing along and give it anything more than just a little gas and then completly let off, my A/F display reads 20.00 (full lean) Also any time I am driving, and then let completly off the gas and manually (I'm an auto) shift it into second and/or then frist to help use the engine to slow down, the A/F ratio display also reads 20.00 and the led light flashes green signaling a lean condition. I believe that this is due to the fuel cut rpm system. This dosen't seem right....:eek: It will read fuel lean until I hit the gas again or for as long as it takes me to come to a slow roll or a stop which can take several seconds... Is there any possable negative side affects to running lean for that long while the engine speed comes down to idle?? Any help would be great!! Thanks in advance!!!

Kris
 

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Don't worry about it, I have the timer aswell and as far as I know this is the way the A/F shit works, when deccelerating your car don't need much fuel couse hey your not on the gaspedal =) It's like the opposite of flooring the shit out of your car, now that's the dangerous part and that's why the Supra injects alot more fuel to the system to prevent you from going lean under boost and such, so as far as I know this is perfectly normal, someone else might wanna explain this further?..
 

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youre not running a atmosphere venting bov are you? this would cause a lean condition...either way though youre going to be getting a rich condition after letting off the throttle as there is no way the ecu can act quick enough to pull fuel...i have a recirculating bov and i can still shoot fire out the tailpipe. as for decel...of course it will show lean, if there is no need for fuel, why inject it?
 
J

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First:

The ECU is programmed to cut the fuel out at higher RPMs when the TPS reads at idle. This saves on fuel, reduces nasty emissions, and helps bring the engine RPM down. It can be safely assumed that when the TPS reads idle, you probably aren't looking to make power... Once RPM drops below the 1200 RPM threshhold, the fuel is turned back on to keep the engine from stalling. FWIW, it won't shut the fuel off unless RPM is over about 2500 or so.

Second:

You're right. But lean is only a danger when there's ALMOST enough fuel. No fuel at all won't detonate, because there's nothing there to burn. Fuel should return as soon as engine RPM comes under 1200 regardless of vehicle speed. At that time, the engine will be running in open loop mode under control of the idle speed controller, so you might get some rich/lean variation depending on how close your open loop fuel map is. (More likely rich than lean)
 
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