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Engine misfires -> Cat Converter fails

Hi,

A few weeks ago in an afternoon I'd parked my Miata at an underground parking lot. When I was ready to leave I started my car to find it idling high at around 1500 rpm, which is not unusual considering the low temperature at that time. However, even at that rpm the car felt like it was going to stall. The check engine light was flashing for some time before staying on. There was a big drop in power and I had to keep the engine speed high (above 3000 rpm) for anything close to the normal amount of power. After the engine had warmed up the idle rpm dropped to just a few hundreds RPMs.

By the time I arrived at my garage the car seemed to have returned to normal. The OBD code indicated engine misfire. Since I just had my spark plugs and wires replaced last year, my mechanic thought we should just reset the computer and see what happens.

The next day the check engine light came on again. This time it pointed to the catalytic converter. I have since learned that a flashing check engine light means that the engine is misfiring, and driving the car in this condition for even a short time can damage the catalytic converter.

I'm just wondering if anyone else has similar expereinces. Any guess as to the cause of the engine misfire? How much will a cat converter replacement cost?

Thanks. Victor

2000 Blue
Reply to
Victor
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The cat is covered by an 80,000mile/8year federal warranty. If you have less than 80,000 miles on the car, a Mazda dealer is obliged to replace a defective cat free.

Reply to
Chas Hurst

Reply to
Chuck

Reply to
Victor

you never mentioned the year miata you are talking about. but models around

99-01 had issues with the coil pack with symptons that match your description. once that is sorted then you can obtain a very inexpensive bolt on replacement cat from rockauto.com (but be aware that they also sell weld on replacements that you may not want if you are doing it yourself).
Reply to
Christopher Muto

Reply to
Scott Streeter

It goes something like this. Random misfire-- may be infrequent enought to turn the ECU light on. (Pending codes, but you would only know this if you had a good code reader.) Front O2 sensor has a possible failure mode less than catastrophic, and this may set occasional cat efficiency codes, which clear by itself, or be can reset and not reoccur for some time. (days, weeks, or even months)

Anyway-- if the cat is not clogged up, running the car at highway speed for a couple of hours may clear it out. There are chemicals that supposedly help, but I don't know about the real usefullness of them.

When in doubt, replace the front O2 sensor. It may seem to have the required voltage output, and be slow to respond, eventually causing the cat efficiency code to set. The front O2 sensor sees "raw" hot exhaust, so it is more likely to have a problem than the rear sensor. A Bosch "universal" sensor should work. Mechanics hate them, because the instructions dealing with the various wire colors and splicing are not easy to understand. (Requires some thinking)

Reply to
Chuck

My miata is from year 2000. The engine hasn't misfired since. How can I determine whether the coil pack is the cause? What do you mean by "issues", and how is it fixed?

Thanks. Victor

Christ> you never mentioned the year miata you are talking about. but models around

Reply to
Victor

"issues" translates to coil pack failures with odd symptoms. Random Misfire being one. I'd assume that with 100,000 miles the ignition wires may be dried out. That coupled with a cooling engine and possibly a damp garage can mean trouble.

So-- Replace plug wires (& plugs) Use NGK "Blues" wires from dealer or other more reasonable priced source. NGK plugs per owner's manual (BKR6-44?) If you have no more problems, good for you.

Reply to
Chuck

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