04 XC70 Multiple misfire

[abscate]

Once the engine misfires the cylinder assignment isn't reliable.

A single bad coil won't cause other misfires but it will code for them

[turbotim2]

So I started by clearing the codes and replacing the spark plugs. Started the car it was misfiring and got multi, 1 and 3 misfires. No surprise, the old plugs were not bad and in spec but oh well, new plugs aren't a bad thing. So I started by clearing the codes and putting a new coil on #1. I started the engine, it was still misfiring and gave the same codes, multi, 1 and 3. So I cleared the codes and moved that new coil to #3 and put the original #1 coil back in. Started it and it ran perfectly, no codes, drove around, no codes or issues. So what I had done previously was I got multi, 2 and 4 codes and I had moved the one bad coil (not knowing it at the time) to from 4 to 3 and that is when the codes went to 1 and 3. Not sure why it throws multiple cylinder misfire codes when one coil is bad but that is what it was doing. Maybe another will fail soon, who knows, time will tell!

[jonesg]

So weird.!

[abscate]

Ah..if one bad coil shorts to ground, it can pull the 12V bus low and cause both coils and fuel injectors to go erratic

Do I win a prize?