DIYPNP driving R8 coils

[elior77]

Hey,

I got a customer miata (95) I work on, we installed new genuine r8 coils (red top), I set the dwell to 2.8ms and we get missfire all around... stock coils work perfect before and after the r8.
Same boost same spark plugs.

Any idea ?

Thanks
Elior

[Paul_VR6]

Not sure if the manuals for the pnp cover those coils but general consensus is they need a pnp transistor or tc4427 driver.

[elior77]

Can you please explain a little why it is needed and the stock coils do not need it.

The r8 run wasted spark, same as stock.

Thanks!
Elior

[elaw]

Some (but not all, I've never seen a comprehensive list of which is which) VAG coils have a low input impedance, meaning they put more load on the driver than most other coils. That results in the driver sending a lower-than-normal voltage to trigger the coil, which can cause problems. So for those coils, special driver circuits are used which can provide the higher current that is required.

If you search subject lines for "VAG COP" here there is a lengthy thread about the problem, with various solutions.

[Paul_VR6]

Elaw nailed it. The r8 definitely have a low input resistance as do almost all "current rev" vag coils. The only ones that are high impedance are the Hitachi brand bolt down coils.

Various older revs had input impedance between 300-500ohms and could work but none of the new ones.

[elior77]

Thank you very much for the answers, what pins do I test for resistance ?

Thanks
Elior

[Paul_VR6]

Between signal and signal ground.

[elior77]

I got the TC4427 on the way:



I under stand I need to use it on the PROTO AREA, what will be the in and out ?

Thanks
Elior

[hybrid]

This is the general wiring for them.

[elior77]

One TC4427 for wasted spakr on 4 cyl ?

[racingmini_mtl]

One TC4427 for wasted spakr on 4 cyl ?

Yes.

[elior77]

It works ! thanks

I used two TC4427 for wasted spark 4cyl.

[rickb794]

When using individual coils there are two modes for wasted spark.

Example (for a 4 cylinder)
Wasted spark - uses two signals and the coils are paired
Wasted spark COP - uses 4 signals and the coils are fired in pairs by the MS

[Ghia15]

Sorry to jump in on this.

Can you post a picture of the setup all wires in to the MS3 board please.

I want to run sequential ignition of the VAG COP on a V6. Would I be able to run this on the three chips wires in?

Thanks

[elior77]

I got it on a DIYPNP board, I guess on MS3 it will be the same with 3 chips running 6 cops.

https://www.miataturbo.net/megasquirt-1 ... ils-94896/