Hi,

I've got an NA MX5, which has previously been running the standard 1.8 engine with a few mods (550cc injectors, Toyota COPs (batch fire)) and an e420c. Everything was working fine.

We've just swapped to a frankenstein forged engine - NA bottom end, NB VVT Head with the NB VVT triggering setup - so a standard mazda 4 pin trigger plate behind the crank pulley, standard mk2 crank sensor, CAS on the VVT inlet cam. I followed some of the instructions on here, now the crank sensor is connected to dig input 1, the CAS to dig input 3 via the standard NA wiring loom, with the mk2 trigger settings moved from input 2 to 3. VVT valve is currently electrically disconnected (but has an oil feed).

ECU Triggering is set as:



Cranking the engine shows input from the sensors - in the ECU Data window you can see dig input 1 and 3 flashing away. RPM shows as well. The engine will try and run - it'll cough and splutter, sound like it's running on 1/2 cyls then buck as if it's firing at the wrong time - usually accompanied by a big wheeze out of the air filter.

While it's spluttering we tried getting a timing light on it - and it seems to be way, way advanced - 70-80 degrees. On a clock face, the standard timing scale on the block would be at about 1 o'clock, the strobed marks are showing consistently at approx halfway between 10 & 11. We manually wound the engine over with a spanner on the crank pulley so that the timing mark on the pulley is where the timing light was firing, and it corresponds to one of the nubs on the trigger wheel, so it's almost like the ECU is firing off the wrong set of nubs:



(So with the timing notch on the pulley rotated to the point where the strobe is firing on cyl #1, the bottom red highlighted mark is next to the crank sensor).

In the ECU data section I can see the inputs for both cam and cas triggering - but it's almost like the ECU is ignoring or mis-detecting the CAS data so is consistently firing out of sync.

The VVT cam is retarded and locked, so it's not that. I tried changing the trigger offsets in wari 10 degrees at a time all the way through the cycle and it wouldn't run on any of them. We tried swapping the coil packs round as well, it's running batch fire for the coils..

To try and diagnose a mechanical timing issue, we've tried cranking over by hand to TDC, with the rocker cover off the timing marks on the pulleys are where you'd expect... The position of the cams at TDC matches up to a pic we found on here at:

https://www.miataturbo.net/engine-pe...roblems-72724/

The crank trigger plate is installed the right way round, and only appears to fit in one position as there's a locating dowel. At TDC one of the pips sits just after where the crank sensor is.

Hopefully we've eliminated all of the mechanical timing checks, and as far as I can tell the trigger settings are set as for an NB, and the ECU appears to be getting the timing signals, but is firing everything way off time...

Any suggestions as what to check next? I'm going to try and borrow a 2 channel scope to check the outputs from the cam and cas sensors, are synced as expected but the ECU is seeing signals of some kind...

Thanks

Jon