Misfire throughout the rev range (M800)

[M800]

Hi all,
since I last posted the MX5 has had a new head with loads of developement.

But we still have a problem.
We are getting a pretty bad misfire, randomly, throughout the rev range. Accordingly I'm not prepared to fire the N2O into it until the issue is fixed.
I've taken ref/sync captures and Mark and Ross should have them (Lee from MPC is the tuner).

Since those ref/syncs were aquired I have replaced the trigger point on the cam gear to clean up the sync. It has, nice square wave throughout the rev range.
But the misfire continues ...... if anything it may be worse now than it was before

Just as an adjunct I have piggy backed the ref/sync signal wires back to the original ECU to give me the in-dash tacho. Since rectifying the sync pickup point to give a single pulse (rather than a double.... sometimes) the indash tacho jumps between 1/2 actual revs and actual revs. The jumps don't seem to corralate with the misfire. Does anyone know how to stabilise the indash tacho?

The tacho is secondary, my main problem is the misfire.

I've got another dyno session planned for wednesday, but would like ideas or others experiences or possible solutions as I'm running out of $$$$ to spend on the dyno.

Cheers
Bazz

[Dragon]

Have you got magnetic sensor for ref?
I would try disconnecting the wires connected between ECU and dash to see if the problem stays.

[M800]

Both ref and sync are Hall sensors (standard Mazda units)
If I disconnect the tacho wire from the stock ECU, the tacho stops working totally. If I disconnect the ref/sync signals from the gold box to the stock ECU, I still have the misfire (and the tacho stops totally).

I'm thinking that maybe I'm not getting enough pulses from the sync sender to drive the tacho properly. Prior to the M800 going in I had stock cam gears and a triple pin pickup (two one side and one the other). Now, with aftermarket fidanza wheels I have ony one pin for the sync to pick up on. I thought the stock tacho wouldnt use the sync, only the ref as it's only revs that it needs as an input, not position.

Thanks

[Motec_Master]

Does the missfire come under high load only or even on part throttle???

If it is under high load only you have an ignition problem I would tighten the spark plug gap to find out.
If the problem temporarily dissappears (get better coils and plugs)

Does it rev smoothly on idle??? Is the timing ref sync setting correct

If it is correct you might have a wrong injector current

you might as well check ignition dwell time

Im also assuming your wiring is correct....
Under the utilities tab
Test out puts (coils and injectors) make sure they are in correct firing order


Regards Rashed