Rough start

ALAN REINER

MEMBER
2000 MAZDA MIATA
1.8L
4 CYL
2WD
AUTOMATIC
44,000 MILES

Occasionally at startup it coughs (if this were a carburated engine I would say it backfires through the carburetor That's the sound I get. Then it settles in and is fine. I have replaced the following: plugs, wires, air filter, fuel filter, coil pack (Duralast). The check engine light indicates catalyst. I do not get a check engine light for intermittent misfire. Got that before I replaced the coil pack. Then no more. Any ideas? This car has only 44,000 miles and has been stored every winter. Never in rain or snow. I can't believe a failed catalyst would do this but there you go. Thanks Alan. Rochester MI

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

Welcome to 2CarPros.

Is the code you get a P0420? If it is, you could have an issue with back pressure. Try this. Remove the pre catalytic converter o2 sensor and start the car cold to see if it changes.

Here are a couple links you may find helpful:

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Let me know what you and if that is the code you get.

Take care,
Joe

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Friday, July 26th, 2019 AT 8:27 PM

ALAN REINER

MEMBER
2 POSTS

So. I priced a new catalytic converter and found that for my Miata I could get an entire SS exhaust system with gaskets and hangers and nuts and bolts, free shipping for about $200.00 more. So without pulling the O2 sensor (there's only one and it's downstream of the converter) I pulled off the old system and hooked up the new one with Magna flow converter. Boom! Started without a cough. Cleared the check engine light, and life is perfect. You were right. Idles perfectly, and mileage is up. Power (according to my butt dyno) is better too, I think. It reaches red line fast. Thanks.

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Monday, September 2nd, 2019 AT 6:22 AM

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

Welcome back:

That's great news. It's amazing how back pressure causes problems. You are very welcome and please let us know if you have questions in the future.

Take care and enjoy.

Joe

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Monday, September 2nd, 2019 AT 5:39 PM