Head gasket failure due to excess backpressure?

[Rob Ellis <aellis@xxxxxxxxxxxxx>]

Is it possible for excess backpressure (a blocked cat) to cause an aged
cyl head gasket to fail?  I'm trying to determine the cause of the gasket
failure, and the cat seems suspect.

The car has been running rich (%CO ~1.1, spec says 0.4-0.8)for well over a
year.  I'm concerned the catalyst has melted, but I have no way to test
backpressure (without fixing a pressure guage to the O2 sensor hole).

A compression test gives a HIGH reading for my two remaining "good"
cylinders (~170psi, spec says 140-150psi).  Could this also indicate high
backpressure?

Rob
9/88 325i 147k

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