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  #31  
Old 12-09-2011, 10:01 PM
THE NEW GUY THE NEW GUY is offline
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Re: fuel fuel injection cut off when engine brakes the car

Quote:
Originally Posted by oab_au View Post
I am sure it does the fuel cut off all the time, even in N.
It is to prevent the fuel on the walls of the manifold from vaporising under the vacuum conditions, and causing it to go rich as soon as the throttle is opened.

Harvey.
yes, ecu does FI cutoff when in Neutral, when you press the gas untill certain rpm and release it suddenly. you can see how revs goes down fast until 1250rpm.
about the rich mix as soon as you pres the throttle, the ecu fuel mapping consider enriching the mix only when necesary by controlling the injector on time.
I believe that by pass valve is not completely closed when engine brake except when in cruise control... that would explain why engine brake power is greater under cruise control... this would means that, actually, our ecu does FI cutoff but bypass valve controls the amount of air getting into combustion chambers. Maybe that is why car industry does not use this kind of bypass valves anymore, they replaced it by stepper motors (syncronized cero magnetic slip, fast, precise and huge torque)
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  #32  
Old 12-10-2011, 05:17 PM
oab_au oab_au is offline
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Re: fuel fuel injection cut off when engine brakes the car

Quote:
Originally Posted by THE NEW GUY View Post
yes, ecu does FI cutoff when in Neutral, when you press the gas untill certain rpm and release it suddenly. you can see how revs goes down fast until 1250rpm.
about the rich mix as soon as you pres the throttle, the ecu fuel mapping consider enriching the mix only when necesary by controlling the injector on time.
I believe that by pass valve is not completely closed when engine brake except when in cruise control... that would explain why engine brake power is greater under cruise control... this would means that, actually, our ecu does FI cutoff but bypass valve controls the amount of air getting into combustion chambers. Maybe that is why car industry does not use this kind of bypass valves anymore, they replaced it by stepper motors (syncronized cero magnetic slip, fast, precise and huge torque)
Quote:
about the rich mix as soon as you pres the throttle, the ecu fuel mapping consider enriching the mix only when necesary by controlling the injector on time.
Yes that is normally the process, but the condition that occurs when the throttle is shut on a reving engine it not normal. When the engine is running, the inside of the manifold and runners are wet with fuel, this is accommodated by the ECU injection time, but when you shut the throttle, all that wet fuel vaporises due to the high vacuum. When the throttle is opened again that fuel vapor is pulled into the cylinder to make a very rich mixture that the ECU can not prevent.
Cutting the fuel during this shut down prevents this condition. At the same time the Idle By-pass valve is opened, to catch the engine at 1250 rpm, stepping down, to bring the engine down to a clean idle.

Hence the reason for later cars to use direct cylinder injection.

Quote:
I believe that by pass valve is not completely closed when engine brake except when in cruise control... that would explain why engine brake power is greater under cruise control... this would means that, actually, our ecu does FI cutoff but bypass valve controls the amount of air getting into combustion chambers.
As I have said, the idle valve is actually open during engine braking. It happens on all shut down throttle conditions, even in Cruise Control. Any differences in the amount of engine braking would depend on, if the converter is locked or not.


Quote:
Maybe that is why car industry does not use this kind of bypass valves anymore, they replaced it by stepper motors (syncronized cero magnetic slip, fast, precise and huge torque
No they are just wanting to spoil all our fun, along with 'Torque Control' 'Stability Control' 'Fun Control'

Harvey.
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