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Replaced a faulty (and intermittent) CAS on my 93 1.6, however the car will still not run. Cranks, fires up then dies. Diagnostics still point to a CAS issue however have confirmed with an oscilloscope that the new CAS is definitely sending waveforms to the ECU.

Sooo would like to rule out the ECU with a substitute if any kind soul nearby to Bulli has such a beast available for a quick test.

I should note that I didn't replace the entire sensor, only the black plastic innards containing the electronics. I guess it's feasible that there's another issue with the CAS that's upsetting the ECU causing it to throw up the G signal fault code?

The ECU itself is in pristine condition, inside and out. No visible damage or black marks of any kind. The ECU cubby hole is completely dry with no evidence of previous flooding.

Cheers,

Chuppa

It's not unknown for a poor connection to develop in the CAS plug if there's been some tension on the wiring - worth a check from the symptoms you're describing, either visually &/or by supporting it at start-up or wiggling it around if it if it stays running long enough. As you say ECU sounds ok, but worth a check failing the wiring revealing anything.

I've got a spare ECU for NA6

You're welcome to borrow it. But I will need it back

Can you make it to the Daffys breakfast run sat morning?
Or meet us down at Bulli?

We'll be at Bulli beach cafe from around 830 onwards this Saturday. I'd say I'll be hanging around for at least 1-2 hrs

Stan that's great! Have sent you a pm.

Chuppa


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nothing in my in box at this time

Thanks 93_Clubman, cas plug to ecu continuity tests seem to check out ok.

Here's a pic of the cas pulses as measured at the ecu.



Measuring these pulses is a little hit and miss with the digital 'scope I'm using as the car is literally only 'on' for a second before it dies and the 'scope has some latency when displaying input.

I would have thought, with all being as it should, that the feed from the cas as shown would be good enough to keep the car running?

At any rate it's time to prove/disprove the ecu so I can at least look elsewhere or go back to scratch with this issue.

So frustrating as all I wanna do is drive her!

Thanks again,

Chuppa

StanTheMan wrote:nothing in my in box at this time

Have pmed again Stan, previous PM was from Tapatalk, so who knows?

Cheers,

Chuppa

Chuppa wrote:throw up the G signal fault code?

Appreciate it's thrown the above, which relates to CAS, but symptoms also point to an AFM issue:
https://forum.miata.net/vb/showthread.php?t=324212
https://forum.miata.net/vb/showthread.php?t=318235
Note tip contained in above when working on AFM. Good luck.

Received PM this time. see you tomorrow

So the problem is solved and it turned out to be my own fault.

After following tips and advice provided in this thread (Thanks 93_Clubman) to no avail I pulled the CAS off the engine one more time. I had already taken it off the previous day to A-B resistance readings with the old sensor which at least proved that the old sensor was faulty.

This time I reopened the case to check the alignment of the rotors and bingo!



When changing out the black plastic plug/sensor assembly (pic 1), I failed to notice that only the larger of the two rotors was keyed to the shaft of the CAS, (pic 3). The smaller rotor's alignment relied on correctly lining up the dimple on the surface of the rotor with the corresponding hole of the larger rotor (pics 2 & 3). This I did not do when changing the innards and paid the price.

So after correcting my error I popped the CAS together and refitted and Silvie kicked over and stayed running first go!

Clearly the fact that the CAS was sending pulses to the ECU was good enough to get the engine to fire but the phase error between the two pulses was too great for the ECU to allow the engine to keep running.

So she's running again and in a way I'm happy that I could undo my own stuff-up and don't have to deal with bigger issues (touch wood). The only permanent damage seems to be to my head unit which doesn't seem to have likes the constant on again, off again with the battery.

Thanks again,

Chuppa

Nice.
does that mean you could actually change the timing or is it a case of it just simply not working when not alligned?

StanTheMan wrote:Nice.
does that mean you could actually change the timing or is it a case of it just simply not working when not alligned?

My take on it is that the misalignment puts the pulses out of phase with respect to each other which is not what the ECU is expecting to see. The ECU probably cuts off the fuel as a result.

Chuppa


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Great that you got it sorted!
Sounded like fuel cut was happening, which was why the NA6 AFM was a slight possibility as it contains a fuel cut switch, & given the error code may also have been legacy.