mx5cartalk.com

I may be asking a question no one has experienced, or even a stupid one... I bought my turbo MX5 years ago, already built and tuned. I had to do the water pump last year and that caused all manner of headaches as I didn't take to much notice of how the timing belt and gears came off the front of the motor. I assumed that was all good as I would just put it back on according to the instructions for a factory setup. But that didn't run. At all.

Turned out that the previous owner (or tuner) ground off the pair of (I will call them) trigger nodes on the intake cam gear, only leaving the single (home?) node at the bottom. They also mounted the gear 1/3 of a turn (anticlockwise if I remember right) on the intake cam. Once I replicated this the car ran.
The car is running a Stinger 4424 ECU, and I assume that this ECU must be the reason they did this- but why?

I am about to do a full rebuild on the motor and I don't want to get a tuner to work on it when I finish, I want my son and I to learn how to tune it ourselves, but this question isn't answered (as far as I can tell) by the 4424 user manual...
Thank you for any light you might shed on this...

after reading through it again it probably not what I was suggesting about the intake /exit cam mofification.

I'm not familiar with that ECU, and a quick search doesn't reveal it used too often in MX-5s. But clearly it works currently, and tuning principles are universal so, rock on!

The timing thing does seem weird. What year car/motor are you running? Stock or adjustable cam gears? If you have any photos please post them up, I'm curious about that setup.

Pay attention to the cam lobes, the front lobes of each cam should be pointing outwards when at TDC, that is, the intake's first lobe should be at 9 o'clock, and the exhaust at 3 o'clock. The gears can then be almost any orientation as long as there are 19 timing belt teeth between them (and the crank is also at TDC).

I guess you'll need to search the software or any available documentation for any methods the ECU uses to adjust/offset timing and ensure they're reasonable values.

It sounds like a real custom installation which will lead to a lot of headaches. It's not something I'd recommend to a newbie, as even an experienced tuner will have difficulties.

Thank you for the replies so far.
Yes Bruce- it certainly seems custom- I was told that it was tuned at PITS on the Gold Coast- but that was the best part of ten years ago.
I would think from the comments so far that surely I could get a replacement intake gear with nodes still intact and a base map for the ECU and tune fresh from there?

Lachy- it is a 1998 NB8a with a stock motor and fixed cam gears. it Dyno'd at 169rwkw back then off what I now know were stock internals... am planning to keep stock internals through the rebuild... Now has a 6spd still has the torsen 4.1

Those gears are easy to get hold of . I’ve got a spare one if you need it


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thanks Stan. I will let you know if I can't find a local one when I go looking.