Denso Ignition Coil wiring options

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1

I’m hoping that someone here will have some insight as to why there would be two ways to wire this coil (part# 099700-1070) from the same auto manufacturer using the same part number

Car 1 (turbo):

Pin1: common power to fuse block

Pin2: trigger from ECM

Pin3: unpopulated

Pin4: common ground to engine

Car 2 (non-turbo)

Pin 1: common power to engine

Pin 2: trigger from ECM

Pin 3: common wire attached to ECM

Pin 4: common ground to engine

On the turbo engine, there is a capacitor between the ground wire for the coils and the ground for the engine (that’s what I found on the harness although the diagram shows between coil common ground and coil common power).

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Okay, I found the answer as to why there are four wires on one model.

https://www.tomorrowstechnician.com/coil-on-plug-ignition-the-wired-differences/

“There are two popular flavors of four-wire ignition coils. The first can be found on Toyotas. Three of the wires are power, chassis ground and PCM command signal, just like the previously mentioned three-wire coil. The fourth wire is a diagnostic circuit known as “IGF” and is run in parallel with all of the ignition coils. The PCM provides a 5-volt bias voltage on this circuit. Each coil has integral diagnostic detection electronics, and when a coil successfully fires, it briefly pulses the IGF circuit to ground as a confirmation pulse to the PCM.”

I guess that Volvo decided that they didn’t need the diagnostic circuit on the turbo engine for one reason or another.

Another article on the same site says that the capacitor is for voltage stability to the coils which is what I thought when I saw the wiring diagram.

However that is not how the capacitor was included in the harness. It was wired across the common ground for the coils and the ground for the engine (as if it is for radio suppression).

I guess now I just need to decide what I’m going to do. Leave it “wired like I found it” (I actually spliced it into the non-turbo harness like I found it in the turbo harness). That decision is a complicated one to explain. I really should have laid a brand new harness but I’m short on time and money for this.

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