V8 dual coil setup - how to setup scope?

MotiCSC · Post by **MotiCSC** » Tue Nov 02, 2021 7:48 pm

Hello

Working on Mercedes 500SL R129 with M119 Engine.
Engine has a 2 coil, 2 rotor setup (one on each cam-shaft) and of course, 8 spark plug wires and 2 king leads.

I have 2 secondary pickups, and using 4425A.

Injection is mechanical so no injection pulse to get.
there is a TDC sensor but it does not line up with any of the ignition events

I am wondering how can i setup the scope and identify cylinders with firing order?

jueja · Post by **jueja** » Wed Nov 03, 2021 12:41 pm

Put your 2 secondary probes on each one of what you call the king pin leads (coil wires). Then you need a sync signal from one spark plugs wire on a third channel. Missing a third secondary cable you can use an inductive rpm pick-up or something similar.

MotiCSC · Post by **MotiCSC** » Sun Nov 14, 2021 6:04 pm

Ok so i managed to setup the scope, i have a question regarding the oscillations on the end of the spark.
Please see the difference between red and blue trace.
each one of them is a different coil.

what can you say about the missing oscillations?

jueja · Post by **jueja** » Mon Nov 15, 2021 2:34 pm

This is an idle capture...to get the full picture a snap throttle capture will be helpful....

Cylinder 1 may be running lean going by its first signal, then the second event of the same cylinder shows a much smoother burn line. Capture the secondary over a period of time including a couple of snap throttles an post the complete psd file.

Do you have a specific issue with this engine?

MotiCSC · Post by **MotiCSC** » Mon Nov 15, 2021 5:53 pm

Engine was lightly misfiring under load, you can see the missing oscillations on blue trace, common to all cylinders.

Solved by changing ignition coil.

same capture enlarged attached.

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