CEL Codes: P0420 and P0303

[XM_Rocks]

Three weeks of Miata ownership and my first CEL.

Autozone checked the codes.

Reading the printout's things the codes have in common:

1) Ignition system / spark plug wires etc

2) Vacuum Leak

Anyone get these combined codes before?

Car is a 1999 w/ 68K miles.

BTW Car is running fine.

[sammm]

Search for P0420. Plenty of old threads.

[XM_Rocks]

Search for P0420. Plenty of old threads.

I was wondering if anyone has gotten them in combo.

Coming from the VW World a Vagcom scan pretty much isolated the part.

Not so much here.

The P0420 code in my searches has been mostly isolated to the or the O2 Sensors.

Wondering if anyone had this combo that can point to something more specific?

[MiataMike]

P420 is sometimes the Coil Pack failing or spark plug wires. And the end result is the P420 which is the cat. When the plugs don't fire correctly it leaves unburnt fuel. When that fuel doesn't ignite in the piston chamber it goes into the Catalytic Converter and ignites there. It can also be the EGR Valve or the EGR Port in the upper part of the intake manifold that needs to be cleaned.

[ozone42]

Believe 303 is the coilpack, or at least ignition related. If your coilpack is going and you're not running on all 4 cylinders it won't take long to destroy the cat.

If you can verify/fix the ignition before driving far it may clear up the 420 and you still get some life out of it, but I've heard of many cat's dying this way.

[XM_Rocks]

Ok I will try and test the coil pack and spark plug wires on Saturday with my Multimeter and see if I have any luck.

Anyone want to lend a hand?

[POS Racing]

Anyone want to lend a hand?

Looking at your profile a location seems to be lacking.

[channelmaniac]

A mulitmeter won't always tell you if the coil pack is bad. Sometimes it's a heat related failure - in other words, it might not show up until the pack gets warm or hot.

RJ

[XM_Rocks]

Looking at your profile a location seems to be lacking.

Added!

I live around 183 and MacArthur.

Can trade scratch removal/reduction from my Porter Cable for expertise and help.

A mulitmeter won't always tell you if the coil pack is bad. Sometimes it's a heat related failure - in other words, it might not show up until the pack gets warm or hot. RJ

So do I need to start replacing spark plugs and wires (clear codes)... if it reappears then post cat o2 (clear code)... if it reappears then coil pack etc?

Again the car seems to be running fine... it seems to be running strong.

[cam76034]

Added!

I live around 183 and MacArthur.

Oh yeah, Hillcrest Oaks. I knew it sounded familiar, but when I was growing up there we never called it that. Lots of big oaks on Hillcrest, Summit, etc...Mom still lives there so I go over there often.
You didn't happen to buy that house on Crestview, did you?

[POS Racing]

So when was the last time the car got plugs and wires??

Helpful link - http://www.madracki.com/miata/dtc.html

[XM_Rocks]

Oh yeah, Hillcrest Oaks. I knew it sounded familiar, but when I was growing up there we never called it that. Lots of big oaks on Hillcrest, Summit, etc...Mom still lives there so I go over there often.

Which house is that? I feel a pulling my leg moment coming... "You know the one with the murders..." "The one that was a condemend crack house" LOL

Yep... I live one block over from Summit on Crestview.

It really is a gem of a neighborhood still.

In the summer it sure is nice to see all the big trees with leaves shading the road.

So when was the last time the car got plugs and wires??

Helpful link - http://www.madracki.com/miata/dtc.html

I dont know... I can ask the previous owner but he didnt give me any records with the car.

I paid $4,500... so I wasn't too disappointed with the lack of records.

I also got a Miata shop manual with all of the codes and repairs... the thing is about 7" thick. (no jokes please)

[POS Racing]

I dont know... I can ask the previous owner but he didnt give me any records with the car.

I paid $4,500... so I wasn't too disappointed with the lack of records.

Well set down the PC and put some plugs and wires in it.....

[XM_Rocks]

Well set down the PC and put some plugs and wires in it.....

Ok... that will be my first thing.

It probably needs them anyway.

Any recommendation on type? No plans for FI.

How many starts does it take to clear the CEL if situation has been repaired?

[sammm]

Any recommendation on type? No plans for FI.

Can't go wrong with OEM. You might check this out too.
http://www.miata.net/garage/manifold/index.html

[POS Racing]

Ok... that will be my first thing.

It probably needs them anyway.

Any recommendation on type? No plans for FI.

How many starts does it take to clear the CEL if situation has been repaired?

It's drive cycles not just number of starts for your '99.

NGK Wires are going to be the most popular I'd guess, and NGK OEM plugs are also all the rage.

I have a OBD scanner that can clear all codes, then you can see if they return after you change the plugs and wires, but this weekend my dance card is full.....

[riverracer]

You can disconnect the battery for a few seconds and clear the codes. Then do the drive cycles and if there is still a problem they will come back.

[XM_Rocks]

You can disconnect the battery for a few seconds and clear the codes. Then do the drive cycles and if there is still a problem they will come back.

Good logical idea.

I will try this tonight and see if it comes back by the weekend.

If it does I will start with the wires and plugs and if it returns continue to sink more money into it until I am broke and crying.

[cam76034]

You can disconnect the battery for a few seconds and clear the codes. Then do the drive cycles and if there is still a problem they will come back.

When it comes to clearing codes by this method some folks say disconnect for a few seconds, others say 30 minutes, hold the brake pedal for ten seconds, pull the main fuse, etc...I've done it by disconnecting the battery and leaving it overnight. Harbor Freight sells the readers for $39.

It's funny how these codes always magically appear shortly after you buy a used vehicle. Same thing with my first miata, the airbag light started blinking a week or two after I bought it. Of course the PO said it had never done it before.

New NGK plugs are $1.59 at O'Reilly. I've got some plug wires I just pulled off mine if you want to try that. Heck, I'll even go back to my buddy at we'reHighly and pick another set just to hear him bitch and moan some more.

One more thing, you said it's running strong, right? Then don't go messing around with Seafoam or cleaning the intake or anything like that just yet. Start with the simple fixes and go from there.

[VFR750]

A mulitmeter won't always tell you if the coil pack is bad. Sometimes it's a heat related failure - in other words, it might not show up until the pack gets warm or hot.

RJ

ditto for the plug wires also..............

Put wires and plugs in it, probably needs an 02 sensor also at that mileage.
My 99 used to set the P0420 code several times a week, since installing all of the above its come back once in 6 months.
I am in your area pretty regular, have a scanner and know how to use it. PM me if you need some help this weekend.