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3.2 injectors - are they peak & hold?
Does anyone know for certain how the injectors on the 3.2 are driven? Is it a peak&hold scheme or are they driven in saturated mode?
The reason I am asking is this: Apparently the injectors are of the low-impedance variety. Something on the order of 2.4 Ohm is what I found searching the board. Maybe someone can confirm this. And on the 3.2 they are wired up in parallel. That gives the total impedance of about 0.5 Ohms. If this pack was driven straight from battery voltage one would run 13.8/0.5= 28 Amperes and it would certainly destroy them. To drive low-impedance injector packs one has to limit the current through them. There are different schemes out there. One can use pulse width modulation (PWM) where an initial 1msec pulse is used to open the injectors and then subsequent shorter pulses are used to keep them open while reducing power through the injectors. PWM is nice because it does not dissipate too much power in the control electronics. On the downside the high-frequency PWM signal can create interference. Another way is to monitor the current by a very small resistor and control the current with a feedback design similar to a linear power supply. This more traditional approach will result in substantial power dissipation in the linear transistor since it will have to burn most of the power. The simplest approach is to put resistors in series with the injectors to limit the current. The resistor dissipates the power and limits the maximum current. As far as I understand matters one looses some of the benefits of the peak & hold injectors because the quicker opening times achievable with low-impedance injectors are not realized with this approach. Essentially, you supply holding current all the time treating them similar to a high-impedance injector. Any thoughts and/or knowledge out there? Has anyone monitored the current through the injectors on a 3.2 and can share some information? Thanks, Ingo
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1974 Targa 3.6, 2001 C4 (sold), 2019 GT3RS, 2000 ML430 I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs Porsche "Hammer" or Porsche PST2, PIWIS III - I can help!! How about a NoBadDays DualChip for 964 or '95 993 |
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03-17-2008, 01:59 PM
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sub'd...
series 10 ohmers' for current limiting....../
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Recording Engineer, Administrator and Entrepeneur Designer of Fine Studios, Tube Amplifier Guru 1989 Porsche 911 Carrera Coupe 25th Anniversary Special Edition Middle Georgia |
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03-17-2008, 05:16 PM
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Come on Loren....I do know you're up on this circuit,..!
Give us your all.....or, at least, your technical expertise (only). I'm sure you can clear this up and get the respectful gent's questions answered... / Thanks,
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Recording Engineer, Administrator and Entrepeneur Designer of Fine Studios, Tube Amplifier Guru 1989 Porsche 911 Carrera Coupe 25th Anniversary Special Edition Middle Georgia |
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03-17-2008, 05:17 PM
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 Someone pointed out that the series resistor should be a 0.1 Ohm . I will measure it one more time when I get home later. If it indead is a 0.1 Ohm things make a lot more sense.... We will see.
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1974 Targa 3.6, 2001 C4 (sold), 2019 GT3RS, 2000 ML430 I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs Porsche "Hammer" or Porsche PST2, PIWIS III - I can help!! How about a NoBadDays DualChip for 964 or '95 993 |
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03-17-2008, 05:21 PM
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Join Date: May 2005
Location: Cridersville, OH
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I'm not an electric guru but I can tell you they are low impedance and a pulse width modulation is used in megasuirt.
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75 911 Indian Red- RUFWAN2B 2000 Boxster 2000 & 2007 Dobies www.stahlwerks.com Cages and preparation for your Porsche “People who never make mistakes must get tired of doing nothing” Bill : The origin of the orgy of Porsche |
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03-17-2008, 05:40 PM
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1974 Porsche 911 Targa 3.6
