Originally Posted by LWT
In the carb days, we tested for exhaust restriction or pluged converter with a simple vaccuum gauge. with engine idle reading should be smoth and above 15". watch gauge while slowly open the throttle and watch vaccuum gauge. at 2500 rpm trans in neutral the vaccuum should be equal to or higher than idle. if a restriction is present the vaccuum will go down. at 3000 gauge down to 10" The vaccuum gauge was connected to manufold vac port or tee into the power brake vac line or any manufold vac source. Also have a helper listen to the end of exhaust pipe. at high rpm you will hear a whistel , labor , scram, noise. Listen to the tail pipe of a known good car. I hope this helps.
Unfortunately a diesel has no vacuum..