vacuum gauge

I would "Tee" the vacuum line on the incoming side of EGR solenoid. James

Why do you want the gauge? just for diagnostic or a measure of fuel economy?

Used to be they sold vacuum gauges that gave a relative measurement of fuel economy... Basically how heavy your foot was on the gas pedal. This may have worked for carbureted engines without any ECM. 'Modern' engines have all sorts of crazy control algorithms for spark timing and fuel injection profiles. Makes the use of a vacuum gauge rather confusing if not useless [afik]. If you are just testing, do whatever you have to as if you were setting the ignition timing (I forget on the SL2 what plug you have to pull). This sets a base ignition timing and you can get some good readings from your vacuum.

Oppie