BayouBill

I have a 99' 911 and yesterday when I started the car I felt an engine misfire.
Connected my OBDII meter and code P0301 appeared Cyl 1 Misfire

Does that usually indicate a Spark Plug or Coil issue?

Thanks

DBJoe996

Could be either. How many miles on the car and have the spark plugs and coil packs ever been replaced?

BayouBill

Mileage=106,000
Bought car recently and I have no maint records.
Probably should change all 6 plugs and coils but at this time I'm only going to change coil and plug on Cylinder 1 and hopefully the code wont reappear ...

DBJoe996

Get the upgraded 997 coil packs. To me it would make sense to change out all spark plugs and coil packs.

BayouBill

Thanks for the tip

gbarron

Quickest way to check if the coil has failed is to swap the coil with cylinder #2 and see if the problem follows the coil.

BayouBill

Process of elimination, I like it ...
I'm wondering how difficult is it to change cylinder 1 plug and coil.
I think cylinder 1 is on the drivers side, cylinder facing the rear bumper ...
3 4
2 5
1 6

Paul Waterloo

You could very well have a leaking coolant expansion tank also which is above it. Mine had cracked coil packs, then combine that with a leaking coolant expansion tank that drips, you get the misfire.

Only get the Porsche replacement tank, unless of course, you want to do it more than once.

DBJoe996

3 6
2 5
1 4

Mike Murphy

It’s entirely possible that changing plugs and/or coils results in no change to the code (doesn’t fix the issue). However, if these plugs and coils are super old or in poor condition, go ahead and “check the box,” but there’s no replacement for good, old, troubleshooting either.

gbarron

Yes, it is a bit finicky getting at #1 (and #6) but not impossible with a good tool set. I just upgraded mine to the 997 style and it took about an hour to do all 6 of them.

BayouBill

Gbarron,
Please tell me the process you used to get to plug 1

BayouBill

3 4
2 5
1 6

This is my 1st Porsche but most other sports cars I've owned it was easier to get to the plugs facing you Vs the ones facing the firewall but I'll soon find out first hand ...

DBJoe996

Did you not see my post? And, no plugs face the firewall, but you will have to remove the heat shields and work your way around the exhaust system. The old coil packs with the inset bolt heads are difficult to remove. But the upgraded 997 coil packs are easy to install with a 10mm wrench. Good luck...

ZuffenZeus