EZK Failure with wasted spark conversion

1990 240 DL NA B230/M47. Stage 0, no other issues.

I did a wasted spark install with the Buchka board using a Miata J702T ignitor and the Bosch 2x2 coil. The car runs great with the conversion in place, but twice now, the EZKs have failed out of nowhere. Both times I got a "this isn't running quite right" vibe just before the failure. It seems to run fine indefinitely when I go back to the stock ignition setup.

I'm using the stock Miata harness pigtail for the ignitor, and a Land Rover pig tail for the coil, and the wiring is sound, the solders for the Buchka board installation are fine, and the board works when I transfer it to a new EZK.

I've asked around about this issue a little in my "build" thread, but haven't really gotten anything solid, and I don't want to keep burning up these boxes. So far the only plausible explanation I've received is to make sure the ignitor box is mounted in such a way that it's physically grounded. I have it mounted on a chunk of aluminum as a heatsink, but the assembly is just floating in space.

Any ideas, or other places to look for causes of EZK failure? Any methods for bench testing these to determine the failure point? I'm not seeing anything obviously burned, melted, blown out, or otherwise bad on the Buchka board, or the EZK and daughterboard.

The pictures posted here
https://www.msextra.com/forums/viewtopic.php?f=101&t=70950

shows that the J702T ignitor is not a true logic-level ignitor, but needs high current drivers. The wasted spark board uses a ATtiny24A chip, which probably can't reliably supply enough current and, over time, burns out.

Try using a different dual ignitor, or a pair of the standard Bosch ... 124 ignitors.

bobxyz said:

The pictures posted here
https://www.msextra.com/forums/viewtopic.php?f=101&t=70950

shows that the J702T ignitor is not a true logic-level ignitor, but needs high current drivers. The wasted spark board uses a ATtiny24A chip, which probably can't reliably supply enough current and, over time, burns out.

Try using a different dual ignitor, or a pair of the standard Bosch ... 124 ignitors.

Click to expand...

But the Buchka board is fine, no issues there.

Here's another wrench in the works. I have retained all of the other stock ignition wiring. Should I be removing the stock power stage? Maybe the EZK is working double duty to fire both? Because I definitely have spark at the coil until I unhook it for the dummy relay for the tach to work. This is literally the first I've considered this.

Land Rover pig tale=Lucas electrics=darkness?

2 old for this said:

Land Rover pig tale=Lucas electrics=darkness?

Click to expand...

I live in that darkness now.

The connector is in good shape, though. I'll rob one off a VW next time I get to the u pull it.

I think I misunderstood when you said:

leecatd8209 said:

It seems to run fine indefinitely when I go back to the stock ignition setup.

Click to expand...

Do you mean that it worked with the wasted spark board removed, and the original coil/ignitor? Or did you swap to a different non-wasted spark EZK too?

After it failed, would it run at all after cooling down or sitting for a day?

Have you replaced your CPS recently, or at least unplugged it and cleaned the connector pins?

Leaving the original ignitor wired up should be OK, but disconnect the original coil so that it doesn't try to spark to nowhere and generate extra electrical noise. It is also OK to not ground the aluminum ignitor heat sink block.

[I looked at a picture of the wasted spark board in more detail, and it looks like it has extra drive transistors included, so it should be able to drive high-current ignitors OK.]

When I say I go back to the original ignition, I swap in a different, non wasted spark, EZK, transfer the plug wires back to the distributor, hook the coil back up, and install the coil wire.

After failures it would not run after cooling down. I've even tried both failed boxes again with no change.

I haven't messed with the CPS at all. The first time this happened I ordered a new one, but when it turned out the EZK was the failure, I put it on the shelf for an engine I'm building. (But I'd like to run wasted spark on the new engine, so I'm trying to get this straightened out.)

The only thing the failed boxes have in common is that they're for turbo cars; one was a gold box. The original pink label NA box is the one I always revert back to, and it's fine.

Can you post a picture of how you've secured and wired the wasted spark board within the EZK?

Where are the ignitor's +12v and Ground wires connected?

12v constant - direct from the battery
12v switched - from the alternator exciter wire
Ground - firewall ground for windshield wiper motor

The wasted spark board wiring looks OK (it took me a moment to realize that it was coated in RTV).

For ignitor/coil power/ground, I'd splice into the original coil power wire (blue?) to supply power to the ignitor and coil. For ground, it should go to the bolts on the intake manifold along with the other ground ring lugs. 16 or 18 gauge wire is sufficient.

Have you tried a wasted spark ezk with the original coil/ignitor/plug wires, and the new ignitor unplugged? Adding the wasted spark board shouldn't affect the original functionality.

bobxyz said:

The wasted spark board wiring looks OK (it took me a moment to realize that it was coated in RTV).

For ignitor/coil power/ground, I'd splice into the original coil power wire (blue?) to supply power to the ignitor and coil. For ground, it should go to the bolts on the intake manifold along with the other ground ring lugs. 16 or 18 gauge wire is sufficient.

Have you tried a wasted spark ezk with the original coil/ignitor/plug wires, and the new ignitor unplugged? Adding the wasted spark board shouldn't affect the original functionality.

Click to expand...

It's dielectric grease. I thought I had a water intrusion problem for a minute.

I have run them in that configuration, yes. They work fine, and then they just don't. I could with 100% confidence put this wasted spark board in another EZK today (if I had one with me) and drive for weeks, or even months just fine. All the way up until the point that the EZK fails.

I have had 1 ignitor fail which dropped out two cylinders, and I have a spare ignitor besides the one I've been using. I suppose I could try swapping them for the next time I feel like swapping EZKs and changing the wiring around. The coil is brand new, RockAuto had them pretty cheap awhile back.

I thought about this a bit more, and looked at some old notes, but I can't come up with any simple reason why the wasted spark board could damage the EZK.

The Miata ignitor will draw a little extra power, say ~15mA, from the EZK +5volt regulator, but this should be OK.

The wasted spark wire to the EZK VR circuit goes to the open collector output of a comparator chip. If it accidentally shorted to ground, for instance if it touched the metalized and grounded EZK case, it would temporarily cause a problem (no VR signal) but wouldn't be permanent.

The wasted spark wire to the EZK resistor is the same as the original EZK spark output pin (pin 16). It should already be protected against common faults.

When the EZK failed, did you try to pull diag codes? Did it respond at all, i.e. did you get a 1-1-1 blink code or nothing? (Note, the diag LED will always light up while the button is pushed, even if the probe wire is unconnected from ECU or EZK holes.)

Did you ever have either the old or the new coil powered up but with its spark plug cables or distributor cable removed? I'm wondering if a high voltage spark could have gotten into the EZK box through the new wasted spark ignitor wires, but that would most likely damage the wasted spark board itself.