GregorS

A question for the forum: I've got a 91 Subaru Loyale and it has started tapping (a hard tap similar to a turbo diesel) on startup for a few seconds and again at high intermediate revs. Wondering if anyone knows what might be causing this. The two options that I can think of are knocking due to dirty engine (I drove mostly in the city), or pistons actually contacting valves due to carbonization (yikes!). Any other suggestions and how to fix this? Gregor