Now that I seem to have the starting resolved I moved on to how it was running. It wasn’t sounding or feeling right and was short on power. After checking and doing a few things I got to the plugs and they looked pretty bad with cylinder 6 and 7 being oily and loaded with deposits.
Changed the plugs and the car totally came back to life, which was exciting however I’m wondering what to do about the leak on those two cylinders. Seems like it could be a few things and I’m wondering which of those are most likely and can I tackle them with the engine in the car?
Oily spark plugs
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MrGreenJeans
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MrGreenJeans
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Good suggestion thanks. I looked up the part number and those are for the 32V engines. I should have mentioned mine is a 78 with a 16VScurry wrote: Mon Jul 21, 2025 12:10 pm Not an expert here.
Maybe the sealing rings for the CAM cover. There are 8 of them. 928 104 443 08
Sorry about that. I haven't worked on anything other than 32v. It looks like you don't use them from the PET I have for this year. Maybe Dr. Bob will have better insight than I on this year.
David Kekar
1986.5 928 Garnett Red
Port Ludlow WA
1986.5 928 Garnett Red
Port Ludlow WA
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dr bob
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My 928 experience is much more on the S4+ cars. Still interesting that it's 6 and 7. There's some known history of uneven temps affecting those two, but I have no real understanding of why or how it would affect oil consumption.
If the plugs are just a bit sooty rather than oil coke or ash fouled, it may be a little richer, or suffering from a misfire there. My somewhat old-skuul diagnostic method connects an oscilloscope to a couple ignition wires to watch firing voltage patterns and variations among all the cylinders. With new plugs they should be pretty even. Higher or lower would have me chasing cap and wires on suspect cylinders.
FWIW, I've learned to stick to the factory plug recommendation, and maybe avoid some of the, um, improved plugs. For instance, I thought for sure the Bosch platinum version of the spec plugs might offer longer life. Small firing errors caused a NOx problem identified at annual smog check. A simple swap to the spec copper resistor plugs brought the levels lower, enough to pass.
Let us know what you see as you drive. If you want to try a casual o'scope effort to see the firing voltages, I can share some tips to make it an easy process. I pull mine out a couple times a decade for something. More modern o'scopes are a lot cheaper and a lot better than the dinosaurs I have. Mine are converted from whale oil.
If the plugs are just a bit sooty rather than oil coke or ash fouled, it may be a little richer, or suffering from a misfire there. My somewhat old-skuul diagnostic method connects an oscilloscope to a couple ignition wires to watch firing voltage patterns and variations among all the cylinders. With new plugs they should be pretty even. Higher or lower would have me chasing cap and wires on suspect cylinders.
FWIW, I've learned to stick to the factory plug recommendation, and maybe avoid some of the, um, improved plugs. For instance, I thought for sure the Bosch platinum version of the spec plugs might offer longer life. Small firing errors caused a NOx problem identified at annual smog check. A simple swap to the spec copper resistor plugs brought the levels lower, enough to pass.
Let us know what you see as you drive. If you want to try a casual o'scope effort to see the firing voltages, I can share some tips to make it an easy process. I pull mine out a couple times a decade for something. More modern o'scopes are a lot cheaper and a lot better than the dinosaurs I have. Mine are converted from whale oil.
dr bob
1989 928 S4, black with cashmere/black inside
SoCal 928 Group Cofounder
928 Owner's Club Charter Member
Former Ex Bend Yacht Club Commodore Emeritus
Free Advice and Commentary. Use At Your Own Risk!
1989 928 S4, black with cashmere/black inside
SoCal 928 Group Cofounder
928 Owner's Club Charter Member
Former Ex Bend Yacht Club Commodore Emeritus
Free Advice and Commentary. Use At Your Own Risk!
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MrGreenJeans
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I ended up putting platinum plugs in simply because they didn’t have a full set of copper plugs at the store and I was impatient. The car really came back to life.
I was also suspicious of the fuel filter for various reasons including more noise from the fuel pumps so I changed that today. Feels like a new car. Such smooth easy power. Fuel pumps sound happy again.
With an intermittent cooling fan issue resolved as well we are ready for a short road trip to the mountains!
As far as the oily plugs go I’m going to not worry about that yet, but enjoy how great it’s running and perhaps pull them out in a month or so and see how they look.
Next up is an alternator upgrade….
I was also suspicious of the fuel filter for various reasons including more noise from the fuel pumps so I changed that today. Feels like a new car. Such smooth easy power. Fuel pumps sound happy again.
With an intermittent cooling fan issue resolved as well we are ready for a short road trip to the mountains!
As far as the oily plugs go I’m going to not worry about that yet, but enjoy how great it’s running and perhaps pull them out in a month or so and see how they look.
Next up is an alternator upgrade….