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No Spark, whyyy?!

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So this is an 88 944 Turbo S that has had a Wolf3d V400 for the last few owners, and quite a few years.

It runs a Bosch ignition coil (OEM, part number 729 43004 101 if it matters).

The other day i was in grid at a race and revved up to move forward in line, and it cut out at the top of the rev.

No spark.

Here is what I know:

Coil is good - I have tested/probed, and swapped back and forth with a known good coil in another 944. Primary was about .6 ohms. Secondary I forget the exact reading, but was "normal"

Cam hall sensor is good - getting if i remember right 400ma pulses back while cranking.

Ignition coil negative is getting negative pulse from computer, and between ecu pin and coil post the continuity checks out.

Ignition coil is getting ~12-13 volts on positive side (and reads almost same on negative side with key on)

Still no output.

SO its getting everything it needs and it still wont spark. I have swapped coils back and forth a few times. This last time i actually got it to spark on crank and kick twice. But then after that nothing again.

A friend of mine that is a long-time mechanic believes the ecu driver isnt able to pull a spark from this coil easily.

In the tuning software the "maximum ignition charge time" indicates a suggested value of 1.200mS to 3.000mS, and it is/has been since I've owned it set to 2.990mS so the upper range of that, which i would think supports my friends hypothesis that its working hard to spark this coil.

Does that seem reasonable?

Do I need to go about finding another coil that fits better?

What the heck?!

I will add that BOTH coils, which run on my other car, you can feed 12v to the positive, and manually trigger the negative, and the coil itself wont spark out the lead, but the negative you just used to trigger will spark. That usually indicates a bad coil, however, both will run my other car no problem.

It's sounds like you have a bad coil driver in the ECU, have you tried looking at the circuit board?

I have not. I can pull it apart today, but what exactly am I looking for?

Could you have a bad engine ground? Look for excess resistance between the head and the battery negative, and/or ECU ground/batt negative.

Is the Spark Plug OK?

^^ I am testing with engine completely bypassed.

Pulled apart the ecu. Have a VB921ZVFI coil driver. Could this be getting weak? I don't know how to test. No oscilloscope...

I even tried upping the dwell from 2.99 to 3.49 and 3.75, nothing.

Both cars read 12v on pos coil, and 10.5ish on negative side while cranking. But one car sparks, other does not. This is making me crazy.

Alright so I replaced the vb921 with a bip373 and am up and running again! I don't know how I should adjust dwell or if I really need to...