So it's been a few weeks - I pulled off the exhaust, heat shield, coil packs and plugs and stuck my boroscope down each cylinder.
All great; no bore scoring on any of the cylinders. Piston heads look great too, for example this is cylinder #3.
Problem: at cylinder #6 we can see an imprint of a valve on the piston head :( No evidence of any metallic fragments or broken valve in the actual cylinder, and no cylinder wall scoring.
Diagnosis: After a bit of research, the most likely explanation is a stuck exhaust valve in cylinder 6. This would explain the initial presenting problem of a misfire, plus the noise heard on the last startup.
Best case scenario - lower or drop engine, remove bank 2 cylinder head, send to a machine shop for repair and refurbishment, reinstall and we're good to go!
Unsure if I can be bothered to be totally honest - this car has been up on jackstands in my garage for half a year while I've been busy upgrading/replacement a bunch of other parts... maybe it's time to grab a new project?
What I'll probably do is advertise the car as-is and see what offers I get. If they're all lowball offers, I'll leave the car in the garage until I get the motivation to research the procedure, drop the engine and pull the head off. I'll probably need a professional to help put it all back together again, that's the only part I'll outsource.
So I'll put together a condensed history of the car here that I can direct interested buyers to.
Summary: 1999 Porsche 911 (996) tiptronic cabriolet, 258,853km. Black body and roof, charcoal wheels. In my ownership since February 2018 at 246,498km.
The main problem:
Cylinder 6 stuck valve as described above. Requires bank 2 cylinder head removal, refurbishment and reinstallation. I have a video from mid July 2021 of the car idling beautifully after replacing all sparkplugs, as well as a video of the startup where you could hear ticking noise of valve impacting on piston head - car was only run for a few seconds, then shut down and not restarted since.
- Obsessive enthusiast owner (me). Pages and pages recorded on excel spreadsheet and receipts/photos available for just about every part, some procedures have been put on this blog.
- Oil changes every 5000km during my ownership. Log books available
- Not under any finance, will supply VIN number for your PPSR report.
- 2 keys and books. Great external condition, 9/10. Interior 7/10, some wear as expected from a 22 year old car, minor marks on some interior panels, and wear on right side of drivers bolster. Some minor marks on 3 wheels.
- Driver's side door latch not keeping window dropped on closure; a common problem. Car comes with an aftermarket replacement door latch new in box, not installed.
- Was driving brilliantly until cylinder 6 issue. Pirelli P-Zero tyres with good tread and even wear.
Maintenance and repair history during my ownership
- 2018 April: Repaired rear left window regulator
- 2018 July: New Crank Position Sensor, alternator/starter Y cable, drive belt, alternator regulator
- 2018 September: Replaced centre console hinge
- 2020 May: New thermostat, new water pump, complete coolant flush and vacuum refill
- 2020 June: Removed front bumper for complete cleanout of radiators and AC condensors
- 2020 August: Complete removal and refurbishment of hydraulic cylinders for roof. Replaced boot strut.
- 2020 September: Replaced handbrake switch
- 2020 October: Paint correction + sealant
- 2020 December: Replaced broken rivet for roof cable, replaced roof drains and cleared all drains.
- 2021 February-August: Installed upgraded 997 oil pressure relief valve and spring. Replaced fuel pressure regulator, fuel pump, fuel filter. Refurbished throttle body and idle air control valve. Replaced all spark plug tubes and installed new Bosch sparkplugs.