On my PA-39 the maniflod pressure reading for the left engine will lag approximately 10 seconds before responding. I changed out the gauge and it still does exactly the same thing. It has done this since I purchased the plane. Any suggestions? It is normally aspirated.

Jerry, sounds like you may have a restriction in the manifold line. I would discoonect the line from the gauge
and at the engine and blow air through the line and see what comes out. Blow from the cockpit side to avoid spraying fuel into
the cabin. Also then check for the small "breather hole in the tube to be sure its not blocked up with debris.
Also, if the tube is not original then check that the hole is indeed there.

Gary

Mine was doing the same thing. There is fuel in the MP gauge causing the bellows to gum up and not work as they should. I also found out the MP line did not have the hole in it to suck out the fuel that is backwash into the line when you shut the engine down. Sooooo after sending the gauge back to Airparts for repair due to fuel in the bellows again I along with the A&P re designed the lines on both engines. There is suppose to be a .075" inch hole 4" from where it comes out of the cylinder head. I actually came out of the head went down 2" and back up at 45 degree angle to catch any backwash before preceding toward the rear of the engine. I have put 10 hours on it without no problems and the last time I had a problem within 2 hour. I hope this helps. thanks George

@ Jerry--

I had issues with mine too (PA39 SN147). The fellows at Heritage Aero in RFD tweeked it. Cliff may know what they did, but I think his right hand Rusty was the "fixer" and he flew with me on before and after test flights. You might give them a call.

All the best!

Jim Covington