2005 XC90 T5 Spark Plug Problem - Ground is gone!

[vincentxc90]

I replaced my spark plug at 60K miles and the old plugs were clean, decent & looks reusable. After 30K miles on my new Volvo spark plugs, the car jerked during acceleration at 40-50 mph and there is no Check Engine Light or any code from a basic code reader. The shop ran their test and said coil #5 is dead. It turned out coil #5 and spark plug #5 (the ground electrode are completed gone from the rim) are bad and plug #3 has lost half of the ground electrode). See picture. The rest of the plug looked dirty with carbon (black stuff) on the tip, rim and the threaded body).

The shop replaced all the plugs and coil #5. The car runs fine now and they also suggest a $300 carbon cleaning job insides the engine and the injector,...etc to remove the carbon to prevent it to happen again.

What is causing the spark plugs in such a poor shape in compared to my 1st 60K miles ? What can I do prevent the spark plugs to fail like that again in only 30K miles. I have been using Octane 87 gas for all these 90K miles and been using Costco gas for the last 2 years.

Is the carbon cleaning necessary or I just should switch to a higher Octane gas with better detergent agent?

[abscate]

If you are using Copper plugs the replacement interval is 30,000 miles and half that for hard service. The fancier Platinum or Iridium last longer, like 60-100k miles.

The carbon cleaning job sounds like an upsell - I would skip that.

Missing pieces of spark plugs isnt good.

I think most Volvos run recommended on 91 octane, and 87 is the minimum requirement. I doubt that contributes to the short spark plug life. Engine management would not let the engine knock with 87 octane

[oragex]

Agreed about not doing that 'carbon cleaning'. What they may do may even cause a problem. If you worry about it, remove the plugs with a cold engine, pour 1/2 oz Seafoam into each cylinder, place back the plugs and coils, and let sit overnight. May smoke upon restart so park outside the garage and away from the neighbours bbq. As above, the q is where did the plug electrode go? Hopefully it went past the valves into the exhaust. The plugs don't look that black in the photo, just about normal. Either they were well past done for replacement, or the 87 octane was causing severe detonation especially in hot weather and when driving uphill and that blew the electrodes. Listen for engine 'pinging' when driving close to a concrete road separator with the window open. I'd run the engine only on 91 from now on - especially being a turbo and monitor a little the top end temperature - does it feel overly hot ? Even if the gage stays at 12h. The car has 90k miles? Was the coolant already replaced?
Have a spare ignition coil in the trunk with the tools to replace it, as soon as the engine starts 'missing' on the road, pull over and replace it - important not to drive with a misfire www.youtube.com/watch?v=nDwtZCWU7u8
May also run a little thermostat test www.youtube.com/watch?v=gQxQnuU22Ow

[cn90]

I'd get the telescopic magnet and go down the cylinder to see if you can fish the broken prong out (if it is not ejected through the exhaust valve yet, also, you are lucky the exhaust valve is not damaged yet).

Ignore the carbon cleaning.

I'd use Octane 91 gasoline.

The broken prong happens from factory defect, it will break at the weld or at the 90-degree bend.

See the video: welding happens at time 1:58, bending happens at time 3:56:

[jimmy57]

Spark knock control has a limit. IF you use low octane and drive up hill at certain throttle openings, not hard driving but steeping into throttle but not enough to downshift from 5th, then you could be in knock range where the limit of the control functions is reached but knock continues. The timing retard is first with enrichment being the back up.

[oragex]

Nice image at 4:36 for the spark plug with 4 electrodes (same goes for the ones with 3 electrodes), just one electrode at a time is 'ignited' so the wear is divided by 4 (or 3) to extend the life of the spark plug

[mrbrian200]

He only has about 30k miles on those broken plugs he took out - the prongs should absolutely not have broken completely off. 3 of them look about like they should. Those two cylinders might be running hot, which usually results from a lean mix. Try getting your injectors cleaned (professionally - where they take them out, clean, and test them). You want to get to the bottom of this. If my haunch is correct you run a substantially higher risk of ending up with burnt valves someday on those two cylinders where the broken plugs came out of.

[vincentxc90]

The plugs at fault are Volvo Platinum plugs I bought on-line and should be good much longer than what I get (30K miles). The shop said it could be because of the engine is getting older. Or may be because I did not torque the plug at all and it was looser than it supposed to be. I read lose plug/vibration can cause the ground to break off (not melt off) and the bad plug drives the coil too hard to cause failure.

On the broken piece, should I assume it has been blown out the exhaust if I have been driving it fine for couple weeks with no problem. If it is still inside and causes damage, it should happen right away within ~ 60 min of running. What I am asking is am I lucky or I am still living with time bomb.

Another strange thing: The Check Engine Light was not on - should it? I was thinking it was a transmission problem. I went to AutoZone to read the code but there was none. After another 2 weeks, the repair shop picked up code (missed fired) but the CEL was still not on. Is it because my ECM firmware is too old and lack the better warning feature. I have not visited the dealer since 2009 (warranty is over) so all my firmware are dated back pre-2009 time frame.

[mrbrian200]

It's still going to spark to ground igniting the fuel/air mix, so you may not get a large enough misfire count to trip a DTC/CEL. Merely the effective gap isn't correct. What you end up with would be more along the lines of improper heat range and detonation on the affected cylinders.

[cn90]

Check if the light bulb for CEL is still good.

The problem spark plugs, is it possible that the plugs were counterfeit stuff?