Random misfire, need help

[hatrack50]

CEL light will not stay off, tired of new parts need help.

[cam76034]

What have you done to correct it so far? Plugs, wires???

[hatrack50]

First code was cam pos sensor, new
Next O2 sensor, new
Then crank pos sensor, new and plugs are new.
Now random misfire, car is 01 and new to me. Any help is GREAT

[sammm]

Since it's an '01 it has ODB-II. What is the actual CEL code? Autozone will read it for free if you don't know.

[hatrack50]

P0300 Randon misfire

[POS Racing]

How are the wires coming off the coils?

Did you noice any oil on the plugs or on the boots when you chaged the spark plugs?

[hatrack50]

None at all, looked again today.

[POS Racing]

How old are the wires?

What did you use for Sparkplugs?

[POS Racing]

Source - http://www.madracki.com/miata/images/wiring/00dtc.pdf

TESTS W/CODES - TESTS
Article Text (p. 22)
2000 Mazda MX-5 Miata
For Yorba Linda Miata
Copyright © 1998 Mitchell Repair Information Company, LLC
Monday, May 12, 2003 01:43PM

DTC P0300: RANDOM MISFIRE DETECTED
Condition
DTC is set when PCM input signal from Crankshaft Position
(CKP) sensor signal is irregular. Deterioration or malfunction of
following components and/or systems could contribute to DTC P0300
being set. Possible causes are:
* CKP sensor malfunction.
* CMP sensor malfunction.
* Ignition system malfunction.
* MAF sensor malfunction.
* Intake air system malfunction.
* Fuel system malfunction.
* Purge solenoid malfunction.
* PCV valve malfunction.
* EGR system malfunction.
* Vacuum problem.
* Wiring problems.

[hatrack50]

Put a set of Autolite Plat, pulled them out today and put in some Bosch Plat to see if it was the plugs. Wires look original.

[sammm]

Wires look original.

Change them. Miata's eat wires.

[creek]

+1 on wires. NGK or Magnacore

[Radio-Active]

Change them. Miata's eat wires.

+1

I bought my Mom's 91 miata a set from Napa and replaced them every time it started misfiring or loosing power, approximately every 25,000 miles. The Napa guys used to swear that if she ever lost that receipt, it was the end of that lifetime warranty.

[wrxmr2eater]

Wires may be a culprit, but 01+ wires are not as quickly destroyed. I did replace mine with Magnacores, but I would be more curious about the MAF, as mine went bad. I picked up a MAF from a recycled Protege as they are the same part and much cheaper than buying a new one from Mazda.

[POS Racing]

You sure when the Crank Possition Sensor was installed it had the propper air gap?

This blurb from earlier makes me wonder - DTC is set when PCM input signal from Crankshaft Position
(CKP) sensor signal is irregular.

You had mentioned the Crankshaft possition sensor had been changed.

Here is a screen capture fromn my '99 service manual (I'd figure the '01 should be the same)

[hatrack50]

New wires on the way, and I will check this air gap when I get home today. Thanks for the info

[Walsted]

Put a set of Autolite Plat, pulled them out today and put in some Bosch Plat to see if it was the plugs. Wires look original.

I'm not 100% sure about Miatas, but with previous vehicles, if the car didn't originally come with platinums, the platinums made them run worse. I've had pretty bad luck with Bosch parts on previous vehicles as well. I haven't tried much on the Miata - the NGK wires and copper plugs work, so I haven't tried anything else.

Hope this helps.

[BAM!]

bad gas? just a thought.

[POS Racing]

Well hatrack50 did you every find the cause of your CEL??

[hatrack50]

no , new plug wires ande also got a coil and tried it in both lacatios to see if I had a bad coil.Clear light and drive a day or so and it's back on.