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beepbeep beepbeep is offline
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Join Date: Jun 2001
Location: Sweden
Posts: 5,564

There is nothing magic that happens with injector when boost is raised. FPR makes sure that fuel pressure is raised when boost is raised, so that pressure differential across the injector is constant (usually 3 bar). You usually choose injector size so that they use around 80% duty cycle when engine/mass flow is maxed.

An injector cannot operate "over peak duty cycle". Duty cycle is just a ratio between time injector is closed and open. It cannot go over it means that injector is constantly open. Regarding high- vs- low-impedance injectors, you usually choose low impedance injectors over certain injector size as they open quicker. It's quite hard to find hi-Z injectors once you step over 50lb/s or so. Low impedance injectors are opened with full voltage (roughy 4 amps) and then kept open with lower voltage (resulting in 1 amp hold current). If your EFI has possibility to control low-impedance injectors (= peak & hold) then its only a matter of fitting new injectors.

So to wrap it up: there is nothing special that happens once you raise the boost. You just make sure AFR's are kept in check and injectors are kept between 70% and 90% at max mass flow and you're square. Also, fuel pump must support whatever the flow is at system pressure (usually 3 bar) + boost pressure (whatever it is).

Adjustable FPR is a messy and crude way of adjusting fuel delivery and should be avoided. Injector capacity does not scale linearly with pressure, spray pattern might change with "odd" pressure and fuel pumps will be taxed. It's best to use standard 3-bar FPR.

I don't quite understand how tuner "has concerns" about injectors operating at their peak (and are opening more than 100% ?)? They are operating on whatever duty ratio EFI tells them to. And if they are doing the mapping, it's should be just a matter of looking into fueling maps? If AFR's can be kept on safe margin without running injectors over 90% then it's OK. If they cannot, you install bigger injectors and redo the maps.

Regarding you failed injector: If you operate injector at high duty cycle for prolonged time it might overheat. Also, if you run a low-impedance injector without peak & hold circuitry it will fail (overheat).

There are few things you should ask your tuner:

1. Are AFR's OK troughout the range?
2. What are duty ratios for current injectors?
3. Are current injectors low or high-impedance?
4. Can your EFI trigger low-impedance injectors correctly (peak & hold)?

Thank you for your time,

Last edited by beepbeep; 11-09-2008 at 12:50 PM..
Old 11-09-2008, 12:47 PM
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