Wiring sequential LS2 coils

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thev's
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Wiring sequential LS2 coils

Post by thev's »

Hi, Just putting my wiring harness together to power 4 LS2 coils sequentially on a Miata. Had a question about the signal ground to MS3 (Pin B) - I assume since the coil switching is coming from the MS3X board it would be better to ground to this rather than the main board ? Is it OK to join the 4 grounds together on the engine and run 1 wire back to the controller rather than one for each coil ?

Thanks

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nathaninwa
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Re: Wiring sequential LS2 coils

Post by nathaninwa »

Yes, you can tie them all together into 1 wire. Tie it to sensor ground, where the coolant,tps, air temp all tie into.
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Healey3000
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Re: Wiring sequential LS2 coils

Post by Healey3000 »

Hi,

Since I don't have an MS3 (yet), I can't speak from experience with this system. However, traditional wisdom says that grounds should be kept separate depending on function. Typically, high current grounds can set up offsets in board traces, which can cause noise on analog channels.

My general approach is to have a separate ground for high-current returns, logic-level grounds and analog grounds. It would be good to know what the user community has to say based on usage.
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Re: Wiring sequential LS2 coils

Post by nathaninwa »

My power grounds are connected to the head, ms logic grounds all tied to sensor ground.
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Re: Wiring sequential LS2 coils

Post by dontz125 »

Healey - I agree with you completely. That said, you may be missing the point that pin B IS a logic ground, with only a handful of mA flowing through. Pin A is the heavy power ground, and it does get wired to the head.

Edit - sorry, you're talking about separating logic and analogue here, not power and logic. The current flow is still so low, and the connection made at the board, that it makes no difference here.

I agree that if you had some low-resistance VAG coils in wasted spark combined with your TPS and MAP signal grounds it would make a total mess of things.
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prof315
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Re: Wiring sequential LS2 coils

Post by prof315 »

I personally don't even bother with the logic ground on LS coils. I just run power, power ground (to the head or block) and trigger. I haven't had a single issue with mine that way for almost 2 years now
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Re: Wiring sequential LS2 coils

Post by Ollie8974 »

All pin A are tied together and all pin B are tied together in the stock harness.
Last edited by Ollie8974 on Mon Mar 31, 2014 6:22 am, edited 2 times in total.
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Re: Wiring sequential LS2 coils

Post by Ollie8974 »

Moderator please delete this double post.
Last edited by Ollie8974 on Mon Mar 31, 2014 6:21 am, edited 2 times in total.
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Re: Wiring sequential LS2 coils

Post by dontz125 »

prof315 wrote:I personally don't even bother with the logic ground on LS coils.
?!
Ollie8974 wrote:Pin A and B are tied together in the stock harness.
Ok - that makes a lot more sense ...
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elaw
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Re: Wiring sequential LS2 coils

Post by elaw »

Perhaps Ollie can elaborate, but I took his post to mean that all the "A" pins are tied to the other "A" pins, and the "B" pins are tied to the other "B" pins, but not that "A" and "B" are connected to each other.

IMHO connecting the "B" pins to nothing is a terrible idea. Connecting them to the "A" pins, or grounding them at the same point as the "A" pins may work but is not optimal. Best approach is ground the "A" pins to the head or block, and the "B" pins (via one wire, separate ones are not needed) to the Megasquirt. And when grounding them to the Megasquirt when using an MS3X card, they should be connected to an otherwise-unused pin on the *main* DB-37, not the MS3X DB-37. The ground pins on the 'X are power grounds, not signal grounds, and should be connected to the block or head (same place as the main MS grounds) and nothing else.
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Re: Wiring sequential LS2 coils

Post by jsmcortina »

I've just checked the wiring on my LS truck motor and will have a diagram up of the coil loom-let in a bit. I did find though that the coils work ok without the signal ground connected at all (whoops!) (EDIT: I'm using an adapter loom from DB37 to MS3-Pro and one half of the adapter has the signal ground from the coils and the other side is empty... Will be fixed.)
The stock wiring does have this running back to the ECU. The power grounds are grounded to the block/head with ring terminals.

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Re: Wiring sequential LS2 coils

Post by sjf911 »

I run twin plug so 2 LS2 coils per cylinder (an upper and lower plug). I have all of the upper signal grounds connected to one common return to the ECU and all of the lower signal grounds connected to another single return to the ECU.
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Re: Wiring sequential LS2 coils

Post by jsmcortina »

Attached is an extract from the manual showing the wiring of the coil multi-plug on my engine. The colours and function match up with a diagram I found on the 'net.

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Re: Wiring sequential LS2 coils

Post by prof315 »

I realize that the signal ground goes to back to the factory ECU (on a sensor ground) but the whole reason for that is to monitor actual vs commanded dwell times. Having run my D585 LS coils for a couple of years now without the signal ground connected and no adverse effects I'm just saying that you don't HAVE to use the signal ground. Should you? Probably.
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Re: Wiring sequential LS2 coils

Post by jsmcortina »

prof315 wrote:I realize that the signal ground goes to back to the factory ECU (on a sensor ground) but the whole reason for that is to monitor actual vs commanded dwell times.
Do you have any information on that? I had perhaps mistakenly thought it was there as a signal reference. I'm not so sure of that now as my coils have also been running with the wire unhooked.
Having run my D585 LS coils for a couple of years now without the signal ground connected and no adverse effects I'm just saying that you don't HAVE to use the signal ground. Should you? Probably.
Unsure! Mine have been working that way by accident too.

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prof315
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Re: Wiring sequential LS2 coils

Post by prof315 »

I was working at a GM dealership when the LS engines first came out and was sent to school for them. That's what our instructors told us. I had the books from that class somewhere........ Also the LS engines were the first GM products to have actual vs commanded dwell data on the scan tool.
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thev's
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Re: Wiring sequential LS2 coils

Post by thev's »

Thanks all, great info !

In terms of making a decent harness do you guys wrap the wires in anything special - I've seen non tacky silicone tape recommended or perhaps high temp heat shrink would work OK, any other good options ?

Thanks
Ollie8974
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Re: Wiring sequential LS2 coils

Post by Ollie8974 »

elaw wrote:Perhaps Ollie can elaborate, but I took his post to mean that all the "A" pins are tied to the other "A" pins, and the "B" pins are tied to the other "B" pins, but not that "A" and "B" are connected to each other.
You are correct elaw.
All "A" pins are connected.
All "B" pins are connected.
"A" and "B" pins are NOT CONNECTED, to each other.
Something else to be aware of when using the LS coils.
There are differences between the "Truck" coils and "Car" coils.
On the "Truck" coil the plug is smaller then the "car" coil.
The mounting bracket is different between the "Truck coil and the "car" coil.
Which ever coil you are using insure you have the correct wire harness and mounting bracket.
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Re: Wiring sequential LS2 coils

Post by dontz125 »

thev's wrote:In terms of making a decent harness do you guys wrap the wires in anything special - I've seen non tacky silicone tape recommended or perhaps high temp heat shrink would work OK, any other good options ?
I use both the stretch 'n seal tape and heat shrink. Adhesive lined heat shrink for branch splicing individual wires, normal heat shrink for small wire bundles, and the tape for main bundles with lots of wires and branches.
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thev's
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Re: Wiring sequential LS2 coils

Post by thev's »

Cool.

Do you guys recommend 16 Gauge or something else for the 12V and Ground (D and A) and 18 for the Signal and ecu ground (B and C) or not get too hung up on it ?

Sorry bout all the questions just trying to learn from others experiences !
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