I have a 2000 V70 XC AWD Turbo. About 3 weeks ago the check engine light came on. The Volvo shop said I had several cylinder misfires. So I replaced all the plugs (gapped at 0.028) and even the coils. The check engine light went away on its own and the car was running smoothly. Yesterday the light came back on again. I took it to Autozone to have them check it with their meter (saveed $100 bucks ). The diagnostics were the same... several cylinder misfires, catalytic converter failure and vacuum leaks. The Volvo machanic told me once that the Cat Convrtr failure error is normal when you have misfire. So the only thing that I have not checked is the vacuum leaks. Could vacuum leaks cause spark plugs misfires? or is it something else that's causing the misfires? Thanks so much

 

Usually a vacuum leak will not cause a misfire.
You might want to do a compression test.

 

Do you think low compression might cause several cylinder misfires? The tester gave possible causes of Random missfires and one of them was vacuum leaks. This is what the tester diagnosis:

Random Cylinder Misfires detected --- Possible Causes:

• Ignition System Fault
• Vacuum Leak
• Injector Fault
• High or Low Fuel pressure.

This car has always been maintained by a volvo mechanic until I lost my job a few motnhs ago. So now I have to troubleshoot it myself or pay a fortune. I've already changed the spark plugs and the coils. I'm not sure if I gapped the plugs properly. I have a 2.4T whitch I think should be gapped at 0.028. I was also thinkg about replacing the electric part that powers the plugs.. (don't know what's called). I'm afraid it's going to end up costing me more than the mechanic since I'm doing trial and error and already spent over $300 on coils whitch I think were not the problem and I can't rerurn them
Thank you for your reply

 

They say a vacuum leak can cause a misfire but I have never seen it myself.
I am wondering if you have the start of a burnt valve.

It is also a possible bad injector.