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2000 V70 SE (NA), 255K miles, AW55-50SN, Denso
Still chasing our #3 cylinder misfire symptoms. (CEL will illuminate with a #3 coil misfire code).
Have installed both in #3 cylinder to experiment a bit: new Volvo 3-prong plug spec'd for 00 NA V70, and new NGK single-strap copper core plug (BKR6E). Both ended with same the results: #3 plug fouls and no good after 500-600 miles. Sometimes the fouling occurs at quite inconvenient times; like on a road trip, which requires roadside repair. After new plug is installed the car runs fine, until the next fouling event - always #3.
Have followed some of the advice and tips posted here on BB and completed:
- My own PCV glove test (negative).
- New Bosch coil on #3.
- Compression check by reputable local Volvo indy shop: 150 psi in all cyls.
- Borescoped #3 cyl by same indy shop; checks normal.
- Same indy shop confirms PCV system checks OK.
- Indy shop swapped #2 and #3 coils and advised to "monitor."
Fouled plug will have a dry and grey cast to the electrode and porcelain. Not wet and oily. Not white and scaly.
Other checks:
- No coolant loss, no signs of bubbles in coolant tank when engine running. Shop advised to look closely when plug fouls again; if porcelain is cracked, it would signal a coolant leak into the cylinder. (Shop says it might only take a tablespoon of coolant to foul a plug).
I asked shop about possibilities of failing fuel injector or failing O2 sensor. They discounted both of those possibilities (no codes thrown, either).
So, as I consider remaining troubleshooting possibilities I think I'm down to two:
- trace amount of coolant leaking into cylinder
- leaking valve stem seal(s)
Thoughts from the BB?
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