my wife has a 99 volvo s80 and now that we're married, dealing with all its problems has become my problem. i just replaced an o2 sensor on it and am still getting a cylinder 3 misfire code p0303? i switched the coil from cylinders 2 and 3 hoping the misfire would move to cylinder 2, but it didn't ... it's still stuck on cylinder 3. any help would be appreciated, i have no idea where to go from here

 

check the plugs, she may have a fouled plug that is not firing right, since you dont know the history of the car most likely, and it s so cheap and easy to do i would replace all 6 plugs for her with some nice NGK Platinums

 

Try switching plugs then, maybe injectors if that does not solve it, if you know how.

If you do not find anything there, check compression.

 

I switched the plugs out. Is it really possible it's an injector? I had assumed it would give me a different code for that. Does anyone know the chance it's a computer problem? Checked the compression ... it's fine. I'm at a complete loss. I called a repair shop and wasn't left with a lot of confidence in their abilities over mine to diagnose the issue ... unfortunately, it seems to be the only one anywhere nearby. Any additional suggestions would be greatly appreciated.

 

Try a can of Tekron Concentrated fuel injection cleaner.

There are a couple of grounding lugs under the plastic cover which covers the spark plugs and wires going to the coils which are parts of the coil grounding circuit. You may want to make sure they are clean.

Also look at the contacts in the connector which plugs into the number 3 coil to see if it is damaged in any way. You may want to do the same for the connector on the injector.

Good luck

 

Very rarely do injectors go bad. If plugs didnt fix it and it is a non turbo engine, OEM plugs have three prongs and aftermarket/cheap plugs can cause misfires. BUT this does not pertain to you. My guess would be a compression issue. If a new coil or plug did not fix that single cylinder, I highly doubt it is a injector and can bet it is low compression due to sticking piston rings. This is caused by carbon build up due to poor maintance intervals and/or low quality oil. Check the compression. If it is low, I can offer a way to clean the rings/piston and attempt to unstick the rings. It works for me 75% of the time at my dealership.

 

It is a turbo, does that make a difference?

 

Only for spark plugs. I highly suggest you check the compression.

 

I have a c70 that has this problem. New plugs and coils. Didn’t resolve it. It’s not as bad but there. When you take it out and get up to speed it’s like it’s firing. Not full potential because you can lightly feel it in your seat . It’s a turbo and it kicks in But when idling the car misses. It was bad where it bounced you. . Is it wiring?? What can I do to clean the ring if it’s sticking? Thank you- Kellie

 

Check compression. If it is low, could be a burned valve or rings.

If you find a low cylinder, pour a tablespoon of engine oil into the cylinder through the spark plug hole and re-check the compression to see if it improves. If it does, probably rings. If it does not, likely valves.

Was the engine overheated?

Are you loosing coolant?