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. 

327 - Looking for Vacuum Leaks

Our fuelie has trouble starting and a vacuum leak is the likely cause.  I removed the cover of the fuel injection unit to take a look. 

This is the connection that draws air from the fuel bowl.  If you stand in front of the engine it would be located on the left side of the plenum.  Although the rubber hose and fittings are an 1/8" or so in diameter, there is only a tiny hole that draws air.  You can see the hole on the inside of the plenum just under the fitting.  No issues here.

This is the fitting for the PCV valve and it's located on the left side of the plenum near the rear.  We have a PCV installed but it might not be the correct one.  The 63 and 64 fuelies had unique PCV's so this might be part of the problem.  It's worth looking into.

This is the vacuum line that feeds the cold start enrichment valve and it's located on the front left corner of the plenum.  This one we want to draw air.

This is the throttle body valve and it's located on the right side of the plenum.  It's 99% closed during the cranking procedure.  I don't see any issues here.

This is a threaded outlet used for power brakes.  Since our Corvette doesn't have power brakes this outlet only gets a plug.  I don't see any issues here either.

I removed and cleaned the plenum lid gasket.  When I reinstall the gasket it looked like this.  The gasket has 4 corners so it wasn't just me stretching it.  There's just too much gasket on the far side.

I decided to replace the existing gasket with a home made gasket.  I cleaned the gasket channel then masked both sides with 1/4" masking tape. 

A tube of high temperature Permatex silicone gasket material was applied then smoothed over with a finger.

When the tape was removed it revealed a very nice form fit gasket.  Double click on the picture for a closer look.  This material takes 24 hours to fully cure so it will sit on the bench until tomorrow.

I am heading back to clean the wheel wells.  It's a crappy job and Ty's not here to do it.  Stay tuned, more to follow.