soot on spark plug

hollywood953 · Post by **hollywood953** » 12 May 2010, 14:51

I removed the coil pack on cylinder 3 and the plug. the plug has black soot at the base of it and the top of the piston in black as well. the CEL came back on yesterday after going off for 3 days. Is it air (not enough) or spark? The wires to this pack are tighter than the others, almost stretched. Might this be my "intermittent" problem as well? It still shudders every once in a while.

Post by **JDS60R** » 12 May 2010, 14:58

Would you please post a pic. It is normal to have a black piston top and flat carbon on the outer ring of the spark plug shell.

With a pic we can tell if the carbon is too cakey and by seeing the electrode we can determine the normal burn temperature.
Can you please post a pic. If not here is a chart. perhaps you can tell us which one is most similar.

http://www.dansmc.com/spark_plugs/spark ... talog.html

hollywood953 · Post by **hollywood953** » 12 May 2010, 15:11

Sorry for not having a camera. It looks like #23 (hot but ok) only the ceramic on the inside is a little whiter it is only 4 months or about 1000 miles old.

Post by **JDS60R** » 12 May 2010, 15:19

Good answer- that just what your plug should look like.
Put it back in and go for a drive - no issues.

What code are you getting ? Failed coil?

Plug seems fine but intermittant fire only occasionally will not change how the plug looks much.

hollywood953 · Post by **hollywood953** » 12 May 2010, 15:35

when i go to autozone it just reads "misfire cylinder 3" it will be fine for a few days then start up again. then fine and so on. Do the wires going to coil #3 arc? could it be this? they are very tight but I don't see a break in the insulation. I checked a few other plugs and they look the same.

Post by **JDS60R** » 12 May 2010, 15:39

The coil may arc but not the wires. If the wires are shorting you willsee the burnt outer casing. If the coil is arcing externally you will see a black dust called corona at the site of the arc. If it is arcing internally (shorting) then you will not see the corona.

Switch the coil with the cylinder next to it and clear the codes. The drive and see if misfire starts in next cylinder. If so replace damaged coil.

Please tell us:
Did you put in the original equipment spark plugs

Post by **JDS60R** » 12 May 2010, 15:42

I am guessing this is the same car you wrote about before.

I believe ti was determined you had a damaged Mass airflow sensor.

Have you replaced it?

If not - you must do that first. Failed MAF can casue an intermittent shudder and plugs look fine.

hollywood953 · Post by **hollywood953** » 12 May 2010, 16:04

My manual says Bosch FR 6 DC, autozone says they don't have this so I asked the Volvo man and he said use Denso. He lso said that with this plug I should exceed the gap of .024 - .028. Your thoughts? When I took the first set out I called the Volvo man and asked him why he gapped them at .032 - .035 and that was his answer

hollywood953 · Post by **hollywood953** » 12 May 2010, 16:08

Sorry JD, as for the MAF I may have misunderstood. I thought the MAF would not cause only 1 cylinder to misfire. I may be way off here. In addition the Volvo man I am speaking of is the repair shop the guy I bought it from took it to for 10 years. He claimed better mileage and power by increasing the spark gap. The first set i took out were Denso as well.

hollywood953 · Post by **hollywood953** » 12 May 2010, 16:43

also, the wires I mentioned being stretched on #3 connector the orange wire is fine but the green w/ red stripe is about 1/4 inch shorter. if I look inside the connector the green one if farther away from the coil by that amount. I am getting ready to drive it after switching the #3 and #4 coils and reconnecting the battery.