Manifold gauge question

[M20F-1968]

I am sorting out a manifold sensor issue.  I installed a JPI 930 and it has their earlier style manifold sensor.  Initially I was using the original aluminum tubing to connect to the manifold sensor.  The manifold sensor was installed to the left side of the engine baffling by adel clamps.  The adel clamps broke twice and the mounting was changed to a hard aluminum block, milled out to accept the sensor.  The mounting now is not a problem.  However, I initially connected the sensor and it worked.  I had to change a mounting bolt and moved the sensor about 1/2".  The manifold gauge started acting in an unreliable manner.  Since then I changed the line to a new flexible rubber line and the 930 still shows variable readings for manifold pressure.  There was a #60 (approx) drill size hole (about 0.040") in the original aluminum line.  I no longer have this breather hole.  It supposedly acts to dampen pressure differences seen from the cylinder.  

 

My question is:

1) should the sensor be taken off the engine baffling and put on the engine mount or firewall to minimize vibration

2) should I introduce a 0.040" breather hold by drilling one of the fittings

3) JPI makes this sensor but no longer uses it - should I just upgrade to their newer sensor.

 

any ideas?

 

Thanks,

John Breda

[carusoam]

The original MP line in my 65C was about an 1/8" diameter, soft aluminum. It had a calibrated weep hole drilled in it.

The parts manual for my C does not have the hole in the drawing. I believe it is just a note on the F's drawing.

I learned about it by speaking by telephone to the test pilot (Bill Wheat) who flew my plane and signed my AF logbook, back in 1965.

It is the tiniest drill I ever bought. It is impossible to duplicate without a proper drill. Also, impossible to get accurate info out of the MP gauge without it. No hole=huge MP drop. Too large hole=barometer.

Now, I will go look if I have the note from 15 years ago....

Best regards,

-a-

John, My handwritten note indicates a 0.023" hole was used. Less than 1/32”. Does this sound like what you are talking about?

I must have saved that note for a reason. I didn't know who Bill Wheat was at the time...

[Hank]

Wow! That's a #74 drill bit! Won't find that at the neighborhood hardware store . . .

[N601RX]

The sensor should not be mounted to the engine baffle.  I had to install a small inline orifice on my JPI 900 to eliminate the pulses and get a smooth reading.  There are several other post about this.