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How to find true base timing ?

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My last built engine was burnt (melted pistons and head) probably because of over advanced timing and pre-ignition, probably caused by wrong base timing.

I will explain what I did and I would love to know how do I make sure the base timing is true... (in order not to kill my new engine or any other...)

I configured the ignition system in the ecu and took out the timing light, the timing light told me -13deg offset for the ecu and that is what I used...

The ECU support told me they never saw more then 3-4deg offset - but that was what the gun told me (simple timing light gun not configurable)

I locked the ecu at 10deg and only at -13deg offset the marks lined up.

After the engine burnt I understood that maybe one of my ignition config was wrong and could advance the timing - "Ignition input Capture" was set to Rising edge and should be set to falling edge.

My new engine is about to be ready - is there any was to make sure my base timing is true ?



What's the engine and what is the ECU? Have you talked to the manufacturer of the ECU and gotten their recommendations?

It is a BP6D - mk2 vvt mazda miata engine 1.8, the ecu is pnp MS3.

The manufacturer saw the wrong setting by mistake when I sent him my tune.

Megasquirt 3. Yeah good luck with that.

Useful input would be appreciated

The BP has a distributor doesn't it? can you not use that and set it up with a timing light?

The BP6D does not use a distributor it uses two coils each is on a plug and near a plug (wasted spark)

Any chance you have a 36-tooth trigger wheel, are using a magnetic crank trigger sensor, and don't have the edge polarity matching the sensor?

If so, try swapping the two magnetic sensor leads, and re-do your timing test. I wouldn't be surprised to see a 5 or 10deg change.

I use an oem trigger wheel pattern on and ATI damper, It does use a crank trigger sensor, what do you mean "don't have the edge polarity matching the sensor" ?


A magnetic sensor has the voltage cross zero with either a rising or falling edge, and the ECU uses this for timing. If the edge does not match what the ECU is looking for you would have timing that could change, particularly with RPM.

Does your configuration refer to "rising edge" or "falling edge". You could just change that and see if the timing is changed to what you expect to see.

The right solution is to use an oscilloscope to verify the crank trigger signal is using the correct edge.

There is another method to check the wiring polarity of your VR sensor, have a quick watch of this video:


What he said -- Awesome video Zac!

Did you check the indicated TCD matched up with the true TDC - usually checked with DTI and degree wheel, but can be close with long screwdriver down plug hole?

I did check for true TDC.

OK, check the ECU is actually reading at the true TDC by setting the timing to zero advance and checking with a timing light, that way you KNOW the datum point is correct and can work from there - if it isn't, the ECU will have an option to enter a correction value for 'tdc' and you just tune normally from there.

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