X-Mozilla-Keys:                                                                                 
David Carter wrote:

David Carter adds an additional perspective:

There are more potential culprits for high MAP readings at idle (over 15
inches Hg) than air leaks.  Assuming NO leaks, then if any other
operating parameter of engine, specifically ignition timing not being
right - assume way retarded - then the engine combustion process is less
efficient than normal and therefore it will take more throttle (open
more) to get a given idle RPM (say 800 to 1000).  That higher throttle
setting itself is what would cause the MAP reading to be higher (16, 18
inches?)   The end result of a scenario like this is that when you reach
full throttle and read 1 or 2 inches less than outside atmospheric
pressure (29 or 28 inches typically, due to air filter and other losses
in the induction system), you will NOT have full rated hp, which is what
you'd expect if timing were not correct.  But, you saw the problem FIRST
when observing abnormal MAP reading at a normal idle rpm - and it wasn't
air leaks.

David Carter

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