Manometer

Today I built a manometer to find out if our motor creates enough vacuum to operate the spill plunger.  A manometer measures pressure or vacuum and is measured in inches of either mercury or water.  It's a simple device and I build one using the basic instructions shown at  http://www.bullittarchive.com/7031.htm

 

To operate the manometer the PVC pipe was filled with colored water...

Then the ruler was positioned at the top of the water column.

 The tubing was attached to the rear of the fuel injection plenum.

 Then, with the coil disconnected, I cranked the motor over and it developed about  3.5" of vacuum.  This is with the PCV valve installed.

 I removed the PCV valve, plugged the hole then cranked the motor again.  This time we got about 4.0" of vacuum.  The PCV valve only took .5" of vacuum.  Not bad.

So what does this mean?

One of my favorite sites for fuel injection information is Ramjets that Run at  http://www.jerrybramlett.net/index.html.  Jerry Bramlett talks about cold start cranking vacuum and states, "Only .5" to .7" water vacuum is needed at the main diaphragm during cranking to generate a good fuel stream at all nozzles."

So, in conclusion, since we only need .5" to .7" water vacuum and we have 3.5", I guess we need to look elsewhere for our cold starting problem.  Next we will investigate the high pressure fuel pump at low RPM.  Stay tuned.