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Injector / Coil Wiring Sizing and schematics

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals


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I am building a wiring loom for an RB20 and was hoping to get some input on the best way to wire the injectors and ignition coils.

My current plan is to run 2 x 20awg ign feeds from the pdm to the bulkhead connector then splice each to 3 on the engine side to feed 3 injectors each.

As for the coils I was planning on doing the same but am wondering will 1 x 20 awg spliced out to 3 draw too much current on single 20awg wire or would it be a safer bet to run 2 x 18awg up to the bulkhead then splice out to 3 x 20awg on the engine side? (Hard to find definitive current draw info on COP coils)

Coils are Toyota Yaris COP, injectors are Injector dynamics 1200's and wiring is M22759 Tefzel.

Also, on the coil grounding side considering the batteries in the boot is it better to ground them directly to the engine block instead of running the earths 3+ meters back to the battery?

Thanks in advance!!

Your power supply wiring plan sounds well thought out, and like it will work well. You would probably be fine running 2 20AWG wires, splitting each to three for your coil power supplies, but if you have the capacity in your connector to accept 18AWG wires, it wont hurt to have a little extra safety factor. What bulkhead connectors are you going to be using? This might have more say in what size wires you're going to run than anything else. Often you're limited on wire sizes by connectors, and if you need more capacity, you run another wire and use another pin location.

Yes, ground the coils to the engine block. Where are you grounding the rest of your EFI system to? I cant off the top of my head remember the yaris coil pinout, do they have a separate ground pin for the secondary winding?

Thanks for your answer Zac. Its a Milspec 55way #MS3470L22-55 which states 20awg size pins but it will accept 24-18awg wire. 18awg M22759 fits into 20awg dtm pins i have here so that sounds like a good plan.

Regarding the rest of the earths the car is running an M600 and PDM 15 so all sensors run back to ECU 0V including shield wires for the mag cam/crank sensors. However i was planning on running the ECU and PDM earths back to the battery but now I will be earthing the coils to the engine I assume it would be better to run the ECU and PDM earths to the engine to eliminate any voltage drops by keeping a common earth point?

The Yaris coils have 4 pins 1)GND 2)Trigger 3)IGF Ignition Feedback which is N/A and 4)12v. So no separate ground pin for secondary winding that I am aware of, is that a thing?!

Thanks Zac.

In my experience, once you get smaller than 18 gauge it gets a lot harder to work with the wire, so unless you have a strong need to not go smaller, stick with 18.

Going to have to disagree with you there Ray, 22AWG is my go-to for any devices where current draw isn't a concern, sensors and smaller solenoid actuators. It ends up being the most common wire size I use. When you build an entire harness out of 18AWG, it gets pretty bulky pretty quickly. 22AWG is still pretty robust, physically, so a pair of 22awg wires heading down to an injector, for example, is reliable.

Ryan - Nice connector! Should be super tidy. Make sure you post up a bunch of pics as you progress, would love to see the progress. I love me an RFB :-).

Yes, I'd ground your EFI harness to the engine, and make it your main star earthing point for the EFI system. Make sure you've got a nice ground strap between your engine and chassis, and then the same between your battery and the chassis, should keep any voltage offsets to a minimum.

Hi Ryan,

First off let me be the first to say im suprised you are running a MoTeC on an RB20, im going to be running an M130 on my RB20 and thought i would be the only person to waste a MoTeC on such a terrible (all things considered) engine haha.

Secondly a single M22759/32-20 12v feed for you injectors will be more than satisfactory, split out to 6x 22awg 12v supplies and then 22awg for ecu trigger.

For ignition a pair of 20awg split into 3x 22awg each for coil 12v would be sufficient also and keep loom size down (which becomes a big factor when running bulkhead connectors!) Yaris coils only need the 3 pins as you have said (12v, trigger and earth) no secondary winding earth required.

And i will also disagree ray, 22awg is the most common wire i use in my harnesses by far, its more that capable of handling most current any sensor needs and its relatively small so keeps size down.

Ryan you better post up some more info/pics of your setup :)