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Today at Atelier Kaz - Private NSX Enthusiast, ex-Honda R&D engineer with F1, Indy/CART background

Eunos Roadster (Mazda MX-5, Miata) Camshaft Angle Sensor – CAS 01

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Started to work on another NSX from last week and I thought it would be an easy task as I serviced this NSX a few years ago and knew the condition.

However, as soon as I tried to move the car to place it on the lift, I smelt the coolant so it was leaking from somewhere.
Already I'm about 2 months behind the schedule and once again, the joy of dealing with the classic car.


The coolant is leaking not only from the header tank but also from the radiator lower left section.

Unfortunately, I already used up my spare Koyo Racing radiator so another one was required urgently.
Once again, thank you to ‘undercaroutfitter’ on ebay US and he sent out the new one on the same day after I placed the order.

Another delay but hope it won’t be too much this time.
I just couldn't ignore the coolant leakage.



And when things are not going to the plan, another thing can happen.
This time, it’s with my Mazda MX-5 Mk1 or in its official name, the Eunos Roadster NA8C BP-ZE 1.8L V-Special II.



As my boss was flying back from Japan with my tools and parts, I thought I better prepare the MX-5 before her arrival.
So, re-fueled the car, quick health check, tyre pressure adjustment for the winter and test driving session.
Everything went smoothly and thought I would move the car over the weekend to install the garage lighting.

Cranked the car as usual but only got the very first catch and nothing thereafter.
The starter was cranking the engine at standard speed and it sounded as if no fuel or no spark after the initial catch.

Unlike the NSX, the fuel pump on MX-5 won’t prime the system unless the ECU detects the crank signal so it's almost impossible listening to the pump sound while cranking.
However, as soon as I released the key after the initial catch, I heard the faint hissing sound for a few seconds from the back so looked like at least the fuel pump was working.

To be sure, activated the relays manually and it confirmed that the fuel pump was working fine.

So, it has to be no trigger signal at the INJ and/or the IG spark.

Connected the timing light at each cyl and confirmed that there was timed IG at #1 and #4 cyl but nothing at all for the #2 and #3 cyl.

MX-5 has only 2 IG coils for firing 4 spark plugs so it uses the wasted spark mode and triggers the spark in 2 paired cyl.
So, whenever #1 cyl gets the spark, #4 cyl will also ignite and same for the pair of #2 and #3 cyl.
Normally, if you don’t get spark at all at the #2 and #3 cyl, you would think that it was caused by the failure on one of the two IG coils as that was the side shared between these two cyl.

However, failure of IG coil won’t stop the INJ from operating so one would expect very rough but #1 and #4 cyl to ignite while cranking the engine.
This was not the case and all four INJ were not operating on the engine.

So, at this point, it became clear that the ECU disabled the INJ due to lack of timing signal.



And it was confirmed by creating simple CEL circuit inside the engine bay.
MX-5 from this era doesn’t have CEL on the dash and the workshop manual has very limited info in this area.
However, if you have LED light bulb (like the T10 one in the video, it's partially broken but I don't throw them away as they can be used on many different things), you can create your own self diagnosis circuit and display the CEL like on our NSX.

I got error code #3 for missing the cyl TDC signal for #1 & #4 cyl and thus, the fuel INJ was disabled.

I only need the tiny electrical circuit board containing the MPU or the hall effect sensor but unfortunately, Mazda only sells the camshaft angle sensor as a big module including the mechanical rotating bearing and housing so it’s not going to be cheap.

I thought about getting the re-manufactured one from RockAuto but the saving was not that big.
I found someone selling just the circuit board but the delivery could take ages so not an option for me.
There was an used unit on the web but no idea how long it would survive.

The existing one survived for 22 years so decided to go for the OEM one and placed the order at my local Mazda dealership as the sensor and o-ring were cheaper than the web based parts companies.


Hope I can make the MX-5 back in operation within a few days.




More delays for NSX services but on the other hand, so glad that this happened at my place where I have access to all sorts of tools for diagnose purpose and not while I was in the middle of nowhere in the cold dark night.

Kaz

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