Misfire under hard acceleration
 

Hello, folks! I hope someone can help me with my wife's 2000 S40. The problem started all of a sudden; when my wife wanted to pass a truck on the highway, the engine started misfiring and the Check Engine light started flashing.
Our mechanic has since replaced plugs and coils, as well as air and fuel filters. No change; the engine still misfires under hard acceleration, although it starts normally and idles and accelerates smoothly if not pressed hard.
The mechanic also mentioned there were codes P0300 and P0304 in memory, but not present...
Any ideas?

Tell the mechanic to throw away the auto-lite spark plugs and use nothing less than platinum's which is the OEM type for this turbo engine.The spark blowout is obvious as the spark isnt strong enough.The codes are corresponding to the problem.

Actually, he said the plugs are AC, but point taken. My wife is on her way to purchase OE plugs from the local Volvo dealer. Will post results as soon as new plugs installed and tested. Thanks!

You were right, GerBeGurGya. Replaced the AC plugs with OE Volvo plugs and the misfire is gone. Well worth the extra expense. Thank you!

Glad you got it figured out. I've found that OEM plugs are the best way to go in my cars (S60R & 854R) with the exception of Bosch coppers in the 04.5+ S40 T5's. Those things rocked!!!

A+ Gerb does it again!

Glad I stumbled across this thread! My girlfriends S40 turbo has the same symptoms. I will get some OEM plugs and see what happens. ;)

:) Just make sure you are getting the Platinums as OEM type for this car.The regular plugs called "copper" belongs to a lawnmover not a turbo engine. :)
Also lets remember that jcjcrespo did replace the coils as well so if you didnt that could be your next thing to look at.

I changed the coils first in an attempt to fix the problem. I will make sure to get the platinum plugs. Thanks! ;)

I have the same bucking/misfiring problem with my 2001 s40. I changed the spark plugs once I bought it about a month ago. The problem stopped for a little while, and is now back. I used platinum spark plugs when I replaced them. I'm going crazy trying to figure out what's going on (as I know little about cars). The ODO II reads a post catalytic O2 sensor when it comes up, which has been 3 times now. Mother of God help me.

When you say you are using Platinum plugs, are these the Volvo plugs? I had tried Bosch Platinum +4 and in my '02 and they did the same thing. The Volvo plugs (which I think are also Bosch) are excellent for these cars and you will not find much benefit in going with an aftermarket plug unless you have a serious tune.

If not the plugs, it could be coil packs & ignition wires.
Stan

Ditto!!!
 

My son has a 2000 Volvo S40 and is having the same problem. Already changed coil and wires and did tune up. I'm going to have to see if he has the platinum plugs. If anyone has any other ideas I would love to hear them. We don't have money to purchase him another car!

I use iridium plugs in both my turbo Volvos. When I purchased Volvo plugs at the dealer I believe they too are iridium, not platinum. You can buy NGK iridium plugs for about $7 each. The OEM Volvo plugs are a bit more. I paid 30 something total.

I like the ngk iridiums also.

I've had misfires from a bad map sensor before, not sure if I had a code or not. It was the one under the shield (we have two).