P0421 - Options... - Page 2 - Miata Turbo Forum -Boost cars, acquire cats.

Welcome to Miataturbo.net   Members

General Miata Chat A place to talk about anything Miata

LinkBack Thread Tools
Old 01-06-2014, 11:51 AM   #21
Destroyer of Inconel
iTrader: (37)
EO2K's Avatar
Join Date: Apr 2010
Location: In ur driveway, abusin' ur WPA
Posts: 8,568
Total Cats: 729

Your problem is ignition related. The 99/00 coil design is **** and its a known problem. Mazda refused to acknoledge the problem and issue a recall but instead they quietly revised the coilpack and changed the PN. If you are still running the factory coil after 14/15 years, its time for a new set of coilpacks.

The failure mode looks like this:
  1. Coil pack gets flakey, causes missfire
  2. Missfire makes car idle rough, dumps unburned fuel into exhaust under load
  3. Surpluss of unburned fuel makes cat go chernobyl
  4. P0421
IGNITION COIL (BP4W-18-10XB-9U) - $305.43 - BP4W1810XB9U

You are going to need to replace your plugs, wires and front o2 sensor but this will not solve anything until you replace the coilpack. Its time to spend some cash and refresh the 14/15 year old ignition components on your car, they don't last forever.

Part of me agrees with 18 because this information is readily avalible if you search, not only here but miata.net, miataforumz.com and clubroadster.net. If the clubroadster guys can figure this out, you can figure this out.

I'm throwing you a bone because I'm in a good mood, and I hate that ******* precat.
EO2K is offline   Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
'01 NB Miata Welcome MoarCurves Meet and Greet 5 10-06-2014 02:57 PM
frank's board in a Rev built MS2 + ReallyRottenTurbo MEGAsquirt 20 08-19-2014 07:58 AM
01+ header swap issue mxamazing Engine Performance 6 08-12-2014 07:39 PM
1999 Mazda Miata - $5700 Dustin Cars for sale/trade 0 03-12-2014 07:46 PM
P0421: Dead cat or bad rear O2 sensor? scenturion Engine Performance 9 09-25-2012 05:05 PM

99, cel, header, p0421

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 07:19 AM.