I have a 2003 496 which developed a popping throught the exhaust when accelerating. It is not constant. It seems its running on 7 cylinders while out the other day it popped then evened out and ran great as if the missing cylinder began firing. After it surged rpn was great but heading in it began to do the same again. Any suggestions on where to start? Fuel injector plugs etc?

Thanks

Could be a couple of things. The first thing that comes to mind is a sticking or burnt valve. Do a compression check and/or run a check with a scan tool.

No codes would a stuck valve pull a code?

Might wanna read here: http://www.offshoreonly.com/forums/g...-iac-hiss.html

My dads did the same thing. It ended up being a cracked spark plug. I would start there. It was a hairline crack that was extremely tough to see to the naked eye, so....

if you have denso spark plugs, replace them no matter what they look like. trust me ive been there on this problem. use ac or ngk. easy,quick,inexpensive (relatively)

lean, or miss fire, valve train issue. i had a customers motor had a bad crank sensor, never showed up on scanner nor did it ever through the service code. had merc send a rep. he was like for the hell of it. pull crank sensor from another motor and re run. we did and never missed a beat.

Ok update pulled all the plugs today they are original densos. All looked fairly normal no real carbon deposits brown insulator but electrode tips looked slightly worn. If it was a valvetrain issue I would think one of the plugs would be black from not igniting correct?

If your 2003 496 has never had the plugs replaced in seven years, then replace them with AC 41-983's and your simple problem may disappear. Always go for the simple fix first, next would be a bad plug wire. Keep IT Simple!

Best Regards,
Ray @ Raylar

plugs are on the way! Ill post and update when installed