Mazda Repair: Miata MX-5 Repair, crank angle sensor, miata mx

Question
Hello Mp2, it's a pleasure to find a site that can assist individuals like myself with mechanical questions that are far and wide to answer myself. First, my concern is, I have a rare 1992 Miata MX-5 automatic, and when you start it up, it responds normal, once you put it in drive and go, the engine lights blinks at times, then it cuts off, just cuts off in the middle of nowhere!!!. This happens sporadically an makes driving undesirable, but not all the time, and mostly in the mornings when the car is cold and warming up. When the car is warm, it runs fairly well, but cuts off periodically. Once it cuts off, at times it's hard to restart, then at times, it just starts normal. I had many repairs done to it so far, an I noticed that when the oxygen sensor was replaced, it ran much better, but months later, it did the same thing, and it's driving me crazy. Second, do these early model Miata MX-5 cars have a history of Oxygen sensor failures? I have no answers and could use your expertise in the matter. The mechanics who have tried to keep me on the road seem to be puzzled of seeing this car in their garage over and over, but have been as helpful as they can in trying to resolve my issues. please help a desperate individual if you can.....

Thank you Mp2 so much for this site, and for helping others who have simular concerns, and thank you for any assistance you can give me personally.
                                        David S.
                                        Stockton, Ca.


Answer
Miatas with similar issues have been through here in the past however, this type fault is rare.

The most common (though rare) has been internal failure of the Crank Angle Sensor (CAS) it provides two signals to the ECU, A "G" signal (TDC of the #1) and an "NE" signal (180 degrees of crank rotation), this item may coincide with your MIL (malfunction indicator lamp) flashing three times as the pre-OBD2 code for this item is 03.  (I doubt it but) If your shop has a Mazda Self Diagnostics System Checker the codes can de downloaded.  This is a pre-OBD2 system tool and very few non-Mazda shops have them.  

The CAS is an electro-mechanical sensor so as with many electronic items it can fail intermittently.  Normally it only fails in one phase of operation the result being a lack of signal on 1&4 (phase 1) or 2&3 (phase 2) but usually not both on a complete rotation.  So if you have spark on 1&4 and no spark on 2&3 (or vice versa) then this is likely your fault.  A failing coil could give similar result since each pack (you have two, 1&4 and 2&3) fires a pair of cylinders however, they tend to not be as intermittent as typically when a coil fails it fails, but not always so it can't be ruled out with out testing.

First check all harness and primary leads for contact corrosion or moisture then move to diagnose and replace parts.  Use Mazda parts, they go the distance (if they went 17 years the first time their likely to go another 17 years.)

Focus on these;
Harness contacts (at the below)
CAS (crank sensor)
Coil Pack (internally burned towers)
MAS (air sensor)

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