P0420 trobleshotting

RichardCrainium

New Member
Ok well I have an intermittent CEL with a P0420 and a P1399 which I understand should be a P0300. The car does not have a miss and I never get only one code when the light comes on it has both codes The car runs fine. I think that I may be dumping fuel and just want a second opinion and a suggestion on how to check. I recently tuned the car up. I had no CEL issues before the tune up. The only reason I did the tune up was because the coil went bad so I did a full tune up.


00 ex d16y8 137k stock ecu
 

RonJ

Banned
Engine misfiring killed the cat.

Despite the tune up, the engine is still misfiring.

Because the information you supplied is so sparse, I can't help you further.

RichardCrainium said:
The only reason I did the tune up was because the coil went bad
Click to expand...
You only do a tune up when a problem arises? Car maintenance is better done for prevention not solving problems.
 


RichardCrainium

New Member
I was told a tune up was done at 120k because I bought it with 122k but I didn't know for sure and I was already halfway there so I replaced the parts at the time. I pulled each wire and could tell when each wire was off. Any suggestion as to how to pinpoint the miss because it is obviously not something that happens all the time? I have no lose of power and haven't noticed a miss at all. The problem is the cel comes on for two or three days 160-300 miles and then its off for 2-3 weeks 1000-1500 miles. All compression is between 190-200(don't remember exact numbers). I recently cleaned iacv because of low idle. Have not had an issue with that since. The car runs well but the intermittent cel is what is throwing me off. If there is a miss why will it go for a while off? What other info you need to point me out. I have heard the downstream o2 can throw a 420 code but don't know first hand.
 

RonJ

Banned
Only a bad cat or exhaust leak throws P0420.

What's needed is to know how you define a tune up. What was done and what brand parts were installed?
 


RichardCrainium

New Member
plugs wires cap rotor coil fuel filter cleaned k&n (properly) oil change pcv valve and lucus fuel injector cleaner. I think that I have a small leak in the exhaust where the headers meet the res pipe but I need to do a oil pan gasket next oil change so I was going to fix it then. I used all OEM parts on the tune up other then the wires I used ngk 8mills. I did see you say to use the plugs recommended In the manual I used ngk platinum's that rock auto says are OEM plugs so if you give me the numbers I will double check that as well. Should I replace the wires with Honda wireset?
 

RonJ

Banned
The tune up sounds fine.

If near or upstream of the primary O2 sensor, the exhaust leak will cause the engine to run rich, so inspect the new plugs for fouling. Fix the leak ASAP.
 
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