MAP testing
 

well im trying to test my map, 1990 4.9, the book says a need a digital meter with frequency setting. that i dont have, i saw a digital meter at checker, $90.00 that says frequency is also on it. any one bought one of these are which one would you recommend. i really dont want to spend a arm and a leg to get one but then it is another tool to have.

i tried my digital dwell tach meter. says to set to 6 cylinder and probe the backside mp/bp, says i should get a reading of 310 rpm, what i see is 32.0 and when i put a vacuum it will go down to 31.0, books says it should go down to 200 rpm