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Injector Drives

EFI Tuning Fundamentals

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Discussion and questions related to the course EFI Tuning Fundamentals

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Hi, so with group fire injectors depending on the A.F.R requirements, these are always working but how the A.F.R tends to be inaccurate? Does the fuel get evaporated when the intake valve is closed causing different A.F.R? Or of what way this happens? And with staged Injection to add this to other fuel drive systems needs plumber work or just changing all the fuel systems that may come designed to use 2 injectors per cylinder, long time ago I saw this in a high-powered R-35 GT-R and I didn´t know-how was that possible.

Hello in group fire the afr in each cylinder will be slightly different because it will only fire the injector in the correct engine timing point on some cylinders depending on the number of cylinders the engine has while the other cylinders will have the valve timing at very different points, it must be noted that this is only minor and rarely has to much effect on the running of the engine, you will notice the fuel consumption higher in group fire mode as compared to sequential to use staged injection you must always remake a second fuel system and wire to suit.

With batched fire sytems, every cylinder gets a half fuel charge on every engine revolution, so for the full cycle they get the full fuel amount.

Some claim this can be helpfull because the first half charge has time to partially mix with the air in the port, others see this as a waste as some will pass out the exhaust on over lap.

As Ross said, with some engine, especially very high power level engines, two, three, or even four injectors per cylinder may be used. There are several reasons for this, such as using one for low fuel supply under low fuel demand, with a second , or more, coming on as the fuel demand increases, because it is difficult to control light fuel demands with large injectors; some will place different injectors at different points of the manifold/intake to give the best mixing; some systems are set up for either potrol/gasoline under light loads and a second one for an alcohol fuel (ethanol or methanol) for higher power when detonation suppression is required or for more power than petrol can provide - sometimes the they switch over completely, sometimes together.

As Ross also said, these are normally set up with independent fuel rails, pumps, etc. and will require the ECU to be capable of controlling these different injectors. Because of the complications, and expense, they do tend to be avoided by most people unless they really need them.

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