PPI/leakdown results after 130k miles
01-27-2011, 05:24 PM
#16
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?I'd love to permanently prevent another SAI-induced CEL, but will first give the conventional remedy a try. It definitely needed the valve guides anyway, so cleaning the ports is really not that big a deal.....that is, until next time.
01-27-2011, 11:03 PM
#17
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Although I readily concede I don't know anywhere near as much about these cars as you obviously do, I have read from more than one source that OBDII cars do retard timing for things such as O2 sensor/knock sensor failures; or even knock detection in 3 degree increments up to a max of 9 degrees. Whether any of those levels are officially labeled as "limp-home" I can't say. However, until I read or hear from a Porsche engineer that a 993 SAI CEL definitely does not retard timing, I'll continue to trust my seat-of-the-pants observations over your slightly modified opinion.
As I said initially, the cost of doing it is insignificant in the scheme of things. However, I'll trust my mechanical observation and ability to assess what's really going on when I have an engine apart. I'm guessing I've had my hand in a fraction (~200) of the number of 911 engines that the rebuilder here has. But once you've got one apart, things become plainly obvious. Valve guide wear. Valve stem taper. Ring land wear. It's extremely difficult to discern where leaking air is coming from sometimes while doing a leakdown. Similarly, I've had more than one engine apart (not necessarily a 911) that's show good compression, but wasn't healthy for the long haul once we could inspect.
