1996 850 Turbo - TWC Damage Solved w/ Spark plugs?

maccampbellsm · Post by **maccampbellsm** » 12 Jun 2014, 19:01

First of all, thank you to everyone who contributes on this site. The amount of information here is incredible. Any forum is only as good as it's users. Thanks RSPI for all of your videos. You've given me great confidence!

When I first got the 850 turbo I replaced the front struts, muffller, battery, PCV system, and spark plugs. Ran great. Fixed other things along the way: Coolant reservoir was cracked, put new tires on, Fixed broken odometer, thermostat, and fixed some cosmetic things.

Then about 6 weeks ago it started to misfire when warm and was getting harder and harder to start. Eventually it was so bad I let my 17 year old daughter drive my car and I started driving the Volvo.

I replaced the fuel filter. Same deal. Checked fuel pressure. It was fine. Ran Seafoam (175Kmiles on her, really bad blow by). Same deal. Was getting codes for misfire on Cyl3, Cyl1, multiple cylinders with TWC damage. Swapped fuel injectors to different cylinders. Same deal. Smelled like gas when it finally starts. Big puff of smoke. Got some new spark plugs.

When I pulled the old plugs ALL of the gaps had moved to a range between .034 and .038, possibly .040. after only 4,500 miles. I set them at .028.

Put the new plugs in. After about 20 start and run cycles it is running right again! I think If I had disconnected the battery and reset the computer the effects would have been immediate.

So what's up with those spark plugs? They were Bosch 7955's from fcpeuro. Is it just because of all the oil I am burning?

Thanks again for all the help here!

Post by **mecheng** » 12 Jun 2014, 20:22

Are you getting oil on plugs? Oil comes from either top PVC hose or oil cap gasket, replace the gasket.
Check the solder joints on your fuel pump relay

maccampbellsm · Post by **maccampbellsm** » 12 Jun 2014, 20:30

mecheng wrote:Are you getting oil on plugs? Oil comes from either top PVC hose or oil cap gasket, replace the gasket.
Check the solder joints on your fuel pump relay

I also replaced the oil cap gasket last year. I forgot to mention that the top PCV hose clamp had come loose and was dumping oil on top on the motor. Found this when I was checking the plugs. Stupid okithier clamps. But still, would that cause the gap to widen so much?

Post by **dosbricks** » 13 Jun 2014, 12:59

The coppers are good in HP applications if you change plugs every 2500 miles. Here is a review of the 7955 plugs someone posted on the fcp site where you purchased them.
"“Went with the bosch copper plugs when rebuilding my engine to avoid the expense of the genuine volvo plugs. I had heard good things on the forums about them. They were great at first but some months later I started getting misfires. I regapped the plugs once, then twice after getting misfires again. Ended up putting the original Genuine volvo plugs back in with unknown mileage and the misfires are gone. I would say these are a good option for high performance applications if changing your plugs with great frequency. If you want plugs that will last for years I would go with the Genuine Volvo kit."

dos