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ischmitz ischmitz is offline
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Join Date: May 2002
Location: Santa Barbara, CA
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Just to re-cap. When the 3.2 DME was developed there were several challenges/restrictions in terms of what electronics was capable off and what injectors were available at the time.

Injectors needed to be low-impedance to achieve the required performance characteristics (short opening times, high dynamic range). So a high-performance injector was low-impedance for speed. The 3.2 fires all six of them at the same time and this compounded the problem: Each injector is around 2.6 Ohm but the net impedance is well below 1 Ohm with all six wired in parallel to the single injector output. That required really huge currents to work.

On the electronic side the technology en-vogue was a BJT transistor. Versions that could deliver enough current had low hFE gains. This resulted in poor conductance and big losses (heat) in the transistor. Because of that a Darlington configuration had to be used. Even then a peak&hold scheme was required with a sophisticated PWM driver. It shocks the injectors open for less than a millisecond and then uses current feedback to maintain a lower holding current via PWM. Additionally the energy coming back from the injectors had to be dealt with by more circuitry. This made the drive circuit very complex by modern standards and required propriety Bosch parts that are NLA.

Fast-forward to today: high-impedance injectors are much faster and perform comparable to their low-impedance counterparts. In addition modern low-side drivers with MOSFET technology can deliver extreme currents with very little losses just like a switch. This makes design much easier. Bosch went to sequential injection in the 964 where each injector has its own channel.

But as others said the old 3.2 DME can drive high-impedance injectors without problems. It's just important that the flow and characteristics are matched or differences are accounted for in the programming of the maps in the DME.

'74 Targa 3.6 (not stock ) - '01 C4 (almost stock) - '00 ML430 (stock)

I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs
Porsche "Hammer" or Porsche PST2 - I can help!!
How about a NoBadDays DualChip for 964 or '95 993
Old 01-15-2020, 10:16 AM
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