Mazda Repair: 2000 Mazda Miata, mazda miata, intermittent faults

Question
QUESTION: Occasional problems starting after driving a short distance when the car sits
for an hour. I wait for 10 minutes and it finally starts, engine light goes on.
Sometimes it starts and feels like it's running on 2 cylinders, I'll drive for
about 3k and then the engine kicks in and runs normal, engine light comes
on but usually resets itself the next day and turns off. 2 mechanics (1 Mazda
mechanic) thought it was a coil problem, tested it, the code did not show and
coils were fine. They both thought it could be a fuel pump issue. The car is a
2000 with only 46k. I bought it in July 07 with only 23k. Maybe the previous
owner let it sit too long and the fuel pump is acting up. If that were the
problem, why would it take a year to start acting up? Both mechanics are
mystified and I have a phantom problem. Do you know what it could possible
be?


ANSWER: Miatas are long term cars, though not flawless.  Most issues are straight forward and revolve around preventative services.  Supposed "phantom" issues can always be explained out.

The ignition coils have been a common problem, they are not easily tested so these results should not be conclusive and the coils should not be ruled out entirely.  The fault is intermittent and random misfire is the code that is displayed as they act up.  In addition the assembly is made up of two coils they seldom both fail.  One fires #1 & #4 the other #2 & #3.

Another common issue is the crank position magnetic pickup, also a hard to diagnose component since it causes intermittent faults as well.  

These are the most common faults and one of them is likely your problem.  The coil replacement should be treated as preventative maintenance, I have seen failures on almost every 1999 and 2000 model Miata I work on.  Both are relatively easy to change.  The CPS pickup requires a gap to contact adjustment when installed.

Fuel pumps seldom fail even with limited use unless the fuel was allowed to sour and reduce to resin (2-3 years no use)

Probability of Failure:
Coils 9 out of 10
CPS 5 out of 10
Fuel Pump 2 out of 10

Hope it gives you some direction, Happy Miataing.

---------- FOLLOW-UP ----------

QUESTION: As per your suggestion, I replaced the coil pack on my 2000 Mazda Miata
which solved 1 problem. The follow up problem was with the rear OE Sensor
which I have replaced. After replacing and driving for a short distance, the
engine light came back on. My mechanic scanned it again and got code 420
with a message saying "make sure there is a software update before replacing
the converter." I will take the car for an emissions test to see if the converter
is the problem. Do you know if there is a software update on the 2000 Mazda
Miata's and could that be the reason why the engine light is on? This car only
has 48k.

Answer
Be sure to have the EGR tube connections checked for tightness or any signs of carbon soot leaking from them.



The coil pack is common.

You seemingly are having overlapping issues.

As for the code.  DTC P0420 is a converter efficiency issue.

It is rare though not impossible that you have a converter problem, low use cars tend to have corrosion issues within the exhaust from lack of use that would normally burn off hydrocarbons and the acids that develop as a result of combustion.

It is very difficult to get an accurate reading on a bad Ho2s sensor on 1999 and 2000 models if the ECU does not point directly at them as a fault.  In other words you may have failure of both Ho2s sensors or the technician may have rolled the dice on which of the two was not reading properly.  In my experience the front Ho2s fails more commonly however, I have had situations where both failed.  Now in all fairness, the code you are getting is rather vague and means the front and rear Ho2s sensors are returning conflicting measurements to the ECU so the MIL is coming on.

The items in question;
Front H2oS
Rear H2os
EGR line leak
Converter failure

It does become a process of elimination which will cost you to get it right unfortunately.  Once the problem is solved, drive it up to highway speeds more often and longer and these exhaust issues will be a long time before they return.

The only software update is with his scanner not with the Miata.