ClemCLone

I've been chasing this for near a month but I have not resolved it.
'05 Boxster, 115K miles
I have a bad misfire on cold startup. Engine struggles to smooth out. After 15-20 seconds, it runs a bit high, 1000-1100 RPM, then settles out.
No CEL thrown,
But I have pulled this code:
P0421 1/1
State: Current
Warm up catalyst efficiency below threshold BANK 1
- - - - - - - - - - - - - - - - - -
This code has only appeared twice when this happened. One tech said positively, the cat on Bank 1 was going out.
Another independent tech from the first, suggests bad ignition coils, based solely on their age. (New plugs last year, coils have no cracks)

Today, After a rough start-up, I get:
- - - - - - - - - - - - - - - - - -
Cylinder 6 misfire detected
Cylinder 4 misfire detected
Cylinder 5 misfire detected
- - - - - - - - - - - - - - - - - -
All on Bank 2

I'm confused, why if the Bank One cat is going, do I get misfires on Bank 2, not on One?
Help me understand.
Thanks

Schwinn

I'm not sure how catalytic issues would cause such problems, especially at startup. Are these cold-startups, or warm starts?

I agree with the other tech - plugs and coils would be my first suspects. Have you ever replaced the coils? If not, then that makes for an even stronger case for replacing those even if they look ok. Cracks aren't the only way coils can go bad... plus if there are fine (not easily visible) cracks that can cause issues.

ClemCLone

This happens on cold startups, as stated. After the car is warm, I get no misfires, none at high speed or under acceleration.
Coils are original.
If bank2 coils are bad, why wouldn't I get constant misfire?

EDIT: I just order 6 Beru Ignition Coils.

Schwinn

If the coils are original, that's likely the issue. On these mid-moiunted motors, they take on a lot of heat and weaken over time. Replacing them is the best first step. Most people recommend replacing them every 80k miles, if not more often. Some people replace them with the plugs every 40k.

Coils being "bad" doesn't mean that they are bad all the time. Temperature, environment, etc can make them work and stop working intermittently. Plastic expands and contracts a lot with temperature, so maybe the cracks are present when cold, and close up when warmed. Lots of possibilities, but it's not worth trying to figure it out to that level of detail... replace them because they're likely worn.

You're on the right track to replace them... let us know how it goes!

ClemCLone

What I had figured, as they are original, it's the easiest, least expensive way to eliminate at least one problem.
yes, I should have done this earlier

ClemCLone

I replaced the Ignition Coils today, new Berus. Before I buttoned it all up, I started it. No misfires, good.
Buttoned it all up, wheels back on, and pulling away from the garage, got a bit of a misfire/hesitation, but it cleared up right away. I ran it to temp and everything is fine.



However, this could have been part of the problem. Cyl #6, broken mounting clip, clean away from the old coil


#6 Plug
Plugs were all good


New coils with E10 bolts

New coils are thicker, 31mm bolts, E10 head. Actually, easier to install with a 3/8's drive, swivel knuckle.


This one is always a bitch

I will monitor this with a cold engine again.
Tuesday: 30 min ago, car fired up to bad missing. Took about 20-30 seconds to smooth out