Modifying GM 3 tower coil for use on BMW and standalone ECUs.

[5mall5nail5]

In case you M30 or M20 guys with Tec3R every want to buy cheap coils, or if anyone running coil on plugs decide that they are far too expensive to have to replace, or if you plain just want to cop my style, I am doing this brief write up to show how to modify a GM wasted spark coil pack for use on any BMW inline 6 motor in wasted spark configuration.

Ok so what I gathered information about this coil pack and found that the unit by default contains a module that controls the dwell among other things. This is unnecessary if you're running individual a standalone with programmable dwell or fixed duty cycle to fire coil packs, so I did away with this module by simply cutting it out.



With an Ohm meter I ohmed the terminals where the coils sit to the pins inside the module area and found that there is one terminal that all 3 coils ohm out to. At first I thought it might be a common ground, but then I remembered that coils are triggered via ground, so it had to be a common +12v, or at least that's my understanding.

Also, based on my own thinkering, it doesn't really matter which terminal I gave +12v or GND, as long as there was each going to each coil. So, technically, even though the coils all share a common +12v (again, my assumption), had I not had this little coil holder thing, I could have just supplied a 12v source to either pin on any coil and a GND to the opposite pin to that respected coil.

Then, once that's established, the other pin on the coil goes each to a seperate pin in the module area and thus I assume they are ground triggers for the coil. If you intend to trigger the coils directly off of an ECU, the ECU must have the appropriate transistors inside to handle coil ignition. Basically, it must have hardware that acts essentially as a mini relay that closes for an amount of time (dwell) and releases (ignition).

The setup cost me $30 and the coil pack came with the aluminum bracket, the 3 wasted spark coils, and the moderately expensive GM HEI DIS ignition module. Some ECUs (megasquirt included) can run with the HEI Module installed but that takes away the ability to control dwell among other things. Because I don't care about the HEI module I ripped it out (which proved quite difficult and interesting. GM fills the cavity that comprises the circuit board up with a unhardening gelatin/silicone or something. Its really nasty shit. It is very difficult to remove as it acts like a glue and a jelly at the same time, yuck). The best part about this is that the coil packs are VERY inexpensive when compared to BMW ones, while providing the same or greated (yes greater) secondary voltage. You see, MSD supplies these high output coils for $40 ea, whereas a BMW high output coil goes for...$$$.

The downside is that I will be running spark plug wires. Downside? No not really, I don't honestly care. It is still a digital ignition system and it will run my motor in wasted spark reliably. Will I go back to BMW COPs? Maybe. My intentions are to run these coils to get the car running and tuned, because right now no one quite understands the BMW dwell timing and with a system such as mine there are too many variables to run the stock coils. I tried - the car wouldn't turn over and I got starter kickback - something was wrong. This will prove to be very user friendly and the funniest part is that the Electromotive Tec3R, although they will not tell you, is basically a user-configurable GM ecu. Anyone with a Tec3R on a M30 or M20 will show you their setup and it looks identical. My buddy had a Tec3R temp sensor fail and I told him to use a GM temp sensor for $7 and lo and behold its identical. So, maybe I revealed the truth behind Electromotive...maybe everyone is already aware - I don't honestly care. I just want to provide people with options!

I sanded the paint off the tops of the coils and renumbered them according to my engines firing order...I think it is correct:



My engine fires 1 5 3 6 2 4, and so I have 1 and 6 on the same coil, 2 and 5, and 3 and 4 on the same coil, for wasted spark of course.

Maybe someone will find this helpful - thanks guys!

[card counter]

Pretty cool.
Your gonna be a electronic guru after this build.

[5mall5nail5]

Pretty cool.
Your gonna be a electronic guru after this build.

It's true - and probably a mechanical one ontop of that. Who knows - just trying to put information out there so people know their options!

[5mall5nail5]

Thought i'd bump this to include some images of today. I managed to mount the coil pack in the car in an optimal spot. When I bought the coil on ebay, and in pictures, I though the thing was pretty small. It is, however, quite large! I ended up removing the aluminum bracket it came with and made a bracket myself.



Obviously they are just mounted in that picture. The stock coils are still in place. I need to measure for spark plug wires and get those probably tomorrow night after work.



I ended up removing that plastic harness cover that runs parallel to the rear hood seal, drilled 3 holes in it. Then, I took the original bolts and welded them to a piece of aluminum bar to hold them in place so I never have to worry about the bolts spinning behind there if I need to remove the coil packs. Works out great.

The hood closes and everything, no worries.

[Robstah]

So, is this the only way of running an MS on the M50? Did you give up on the BMW coils? Keep us updated.

[5mall5nail5]

Its not the "only" way - but since I have.... no one to model my setup after, and I have to figure it out for myself, I figured I'd get the car running on a more "conventional" method. Once I get the car running on this GM coil setup, I can swap over to the BMW COP and I will have less variables to change. The initial start is the hardest part, and if I can get it to go on typical GM coils then I at least know what my settings need to be for the timing and all I have to change is the dwell wen I switch to BMW coils.

[Robstah]

Its not the "only" way - but since I have.... no one to model my setup after, and I have to figure it out for myself, I figured I'd get the car running on a more "conventional" method. Once I get the car running on this GM coil setup, I can swap over to the BMW COP and I will have less variables to change. The initial start is the hardest part, and if I can get it to go on typical GM coils then I at least know what my settings need to be for the timing and all I have to change is the dwell wen I switch to BMW coils.

Good stuff. Good luck on all of this. I know you are the only one out there working on this and I wish I could help, but money and lack of time now a days have been my reason. Just dont give up, you have a lot of people that would love to go your way instead of dropping 800+ per tune, when they can do it themselves.

[EThirD]

You're still using a megasquirt, right. I noticed you mentioned tec3 in the first post.

[5mall5nail5]

It'd work with any standalone... tec3 uses their own coils which are actually just gm units with different covers...

[EThirD]

Well I understand that much, just curious as to your setup.

[vector86]

Is there any chance the pictures from this thread are still floating around somewhere? They seem to be missing.

[5mall5nail5]

Vector I will dig them up tomorrow night

[5mall5nail5]

Vector I will dig them up tomorrow night

[camshaft]

Holy resurrection. I read this thinking this was a new post Jon and that this was DTA related lol.

[5mall5nail5]

Haha nah Austin - old school post. My images from this generation were partly lost when some people stole my site - I have them on backup though. DTA runs stock coil packs, actually I used stock coil packs with MS as well, just not initially.

[thespeedfactory]

Why are you not running direct fire ignition/sequential injection? I thought you were with the DTA.

Cannot DTA run sequential internally?

Just a question to clarify.

[5mall5nail5]

I am, look at the dates of these posts

[vector86]

Vector I will dig them up tomorrow night

Thanks, I'm getting ready to install MS on mine in a little bit.