Miata Mailing List: October 1994, Message #159
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   From: 
Subject: Self-Diagnosis Codes
   Date: Mon, 10 Oct 1994 18:49:53 -0400

Well Miateers,
Since you won't avail yourselves to get myself into more trouble with my 
amateur engine tinkering (except Harvin, thanks Harvin), I have gone the 
full route of checking out the engine coding per the MCA mag and the 
Workshop Manual.  Here's the outcome.

I reported Saturday night after setting my ignition to 14btdc, that my 
check engine light was flashing, and I couldn't figure it out (sort of 
reminds me of "help, I've fallen and I can't get up").  From only getting 
a brief glimpse of it before pulling the jumper it appeared to flash 
three times and then was dark for afew seconds and then flash three or so 
times again.

Reviewing the magazine, all it said was "G-signal."  That didn't help 
much, so, being intelligent enough to have purchased a workshop manual, I 
consulted that compendium of knowledge.  Ahah! For each different code 
that can be dispayed, there is a troubleshooting sequence to checkout 
just why the darn thing is flashing at you.  [For those of you that have 
a manual, look on page F-80 and beyond.]

The G-signal is related to - you guessed it - the Crank Angle Sensor.  
Now the self-diagnosis is supposed to be done with the engine off and no 
fiddling with the parts.  But as you can imagine I was fiddling with the 
CAS while trying to adjust the timing. Expecting that there was something 
related to the timing adjustment (remember I went clear up to 18btdc 
before backing off to 14) that I made, I expected that the signal was 
false.  Therefore it made sense to reset the diagnosis system before 
trying to make any sense of it.

The reset method is to remove the BTN fuse for 20 seconds.  The workshop 
manual says to disconnect the battery, but I suspect that the BTN fuse is 
just as good a method and a lot easier.  With the system reset (don't 
forget to read your radio code and be prepared to reenter it after 
replacing the BTN fuse), I performed the self-diagnosis steps as 
described.  Let the engine rise to operating temperature, short pin 10 to 
ground in the diagnosis connector, turn the key to on and read the 
flashes of the check engine light.

This time there were no flashes.  As Alex suggested on Sunday during our 
Chesapeake Area Miata Fall Foliage Tour, no news in this case is probably 
good news (or words to that effect).  I am comfortable with the results 
and glad to have learned about this BIT (US Military parlance for 
Built-In-Test) capability.

As far as the mileage goes, it looks really good, but as someone described 
earlier (Mike Friedman I think), I can't honestly feel any significant 
increase in power.  Like I said before, I'll give you another report after 
some test time has elapsed.

Thanks again Harvin for trying, and no I didn't call Norm.
Later Gang,
Tom