[mysocal911]

Originally Posted by Showdown

Dave,

These are Denso smart coils requiring 5v logic signal from the ECU to fire them. No output coil driver necessary as with "dumb" coils.

You most certainly can measure resistance on a smart coil and I followed multiple procedures for these coils and of the several I tested, they were out of spec.

Yes, but not actually measuring the primary of the coil itself, you're measuring the input circuitry for the 3-5 amp power device that drives the coil primary (<5 ohms).

Originally Posted by Showdown

I had initially purchased the Audi pencil coils for the car but went with Denso as they were smaller and fit the engine better and have been used by many folks on 911s, including TurboKraft which sells them as part of a kit. As a Toyota product it also seemed logical to think that they were reliable, ubiquitous and economical. I couldn't return three of the the Audi coils (I did return the other three) so I tossed them into a box.

The dwell time I had for these coils was 3.5ms, but I saw that the cranking dwell was 6- I checked my notes and it should have been 4 and I can't recall why it was set to 6, so that may have contributed to fatigue on the coils...

Keeping the dwell time too long causes the voltage of the primary winding of the coil to go to zero volts, over-stressing the internal power transistor resulting in a failure. Assume a coil primary resistance of 2 ohms @12V equals 72 watts @ COP transistor switch once the primary of the coil saturates.

Originally Posted by Showdown

The system is wasted-COP. I considered going full sequential with spark but the cost for an ECU that was capable (and had the other features I wanted) was more than double the cost of the ECU I went with and for a single spark low compression engine I felt the benefits to sequential spark weren't necessarily worth the cost.

Now, perhaps with COP sequential really is necessary as it reduces the frequency of firing and load on the coils. and if I find that to be the case (all research and documentation conducted thus far runs contrary to that) then I'll pull the eCU and wiring harnesses and switch to one that is capable of sequential spark...

New connectors are arriving today and I've already remade the harnesses- I have this weekend cleared to work on the car and hopefully solve this supremely inconvenient problem.

Your existing wasted-spark system should be more than adequate, as long as you don't over-drive the ECU output pulse width to the COPs. You should use a scope to verify the actual signal pulse width the ECU supplies to each COP,
and determine what the minimum is to avoid a misfire. Most importantly, the COP datasheet should reviewed! Each COP only sparks once per engine revolution, so @ 6K RPM that's every 10ms.