Hello everyone,I have a 03 nbfl 1.8 sporty vvt turbo mx5.
Recently I had a problem udner high load at 6000rpm+ the CEL comes on and the engine goes dead for some seconds and then it starts again with a high boom from the exhaust ECU is plugged in and it showed up sync lost reason 31 at the Megalog viewer and at the Tunerstudio while plugged in the VVT box became red.(This doesnt happen all times)
Below is the graph of the Megalog program to show you what exactly what I mean, at the time the fault code occured and as you can see at the graph the car shut off when occured and then it turned up again after some seconds.
What does the (31 = Miata 99-00 - 2 cams not seen) means?
Car Specs:
megasquirt 3
JE pistons
Carrillo rods
2867gtx
stock head
New iridium spark plugs
New crank sensor
car is 290hp.
Any Ideas ?what this will be? maybe cam sensor? thanks!

 

When this happens it is not good.
Make sure your cam sensor and wiring are in good condition. You need to solve this before you cause too much damage.

 

Is it only under high load at those RPMS? Or does it also happen at light load at high RPMs?

I had a similar issue that was strictly RPM dependent. In my case, I had to let the engine completely die (clutch in, let it go to 0 rpm) before it would restart. Turned out to be misadjusted potentiometers in the megasquirt.

 

I will replace the cam sensor and check if the wiring is bad.It mostly happens at 3rd and 4th gear although sometimes it can occur at 1st and 2nd aswell.What did you do when you found that the potentiometers in the megasquirt were misadjusted?
This problem can happen at any rpm not specific at 6k RPM but it doesnt happen everytime it can happen at around 4 out of 10 times when going full throttle.

 

Had to remove the megasquirt, open it up, and correctly adjust them.

However, probably not your issue. Mine was very repeatable and strictly rpm dependent.

 

I hope it doesnt need this because I am not able to do it.
So I will just replace the cam sensor and wiring to see if everything is ok.
Car is 2003 VVT 1.8 maybe something else to check before big problems occur from this issue?

 

I would check your crank sensor and wiring too even though the lost sync reason doesn't point to that. I think some of the wires are shielded and even a little damage to the insulation would make me suspect a possible future problem. Sometimes people don't quite route the wires right and they get a little damaged when reinstalled. I could be wrong but you asked what else I would check.

 

the pot screws are just a flathead screwdriver. nothng fancy