Bouncing oil pressure...
 

I was out yesterday and my port side motor oil pressure started bouncing at higher RPM's. As soon as I pull the sticks back it jumps right back up. Lowest I saw was 18 psi and it would jump to norm 65-70. On idle is normal, I'm thinking it the sender... I kinda poked back there and looked for it but did not see it. When running in chop it seemed to bounce with the way the boat was bouncing. I checked the oil... Level was fine and look me on the stick(only 4 hours on the oil). It was nice and thick(no signs o aeration as far as I could see.

The sender is mounted on the engine block below the # 7 spark plug. Sounds like the wire may be loose.

Or your oil pickup may have come loose.

I'm hoping it's not the tube

test it with a mechanical oil pressure gauge taking the sender right out of the mix plus its connections.

Also make sure your oil level is correct and not over filled. Or making oil

Make sure you are using the correct motor oil viscosity and a quality oil filter. the simple things first and foremost.

I run royal purple and use a K&N filter. I have always ran that setup without issue. I'm prob going to take a look at the sender on Thursady... Se what that brings. Under #7 spark plug ...anomie know if it's the same on small blocks?

What gauge brand at the dash ? sometimes it is very wise to match sender up to gauge package brand. Its about matching ohms of the sender to the gauge. Just saying as a rule of thumb.

Bad sender....

Had the same thing happen on mine. Found some corrosion in the main plug of the engine harness. Cleaned it up, all good.

A cheby is a cheby, the holes are in the same spot, big or small block.........1,3,5,7 down the port side.....2,4,6,8 down the starboard

Livorsi gauge..... It had grafrigs from the factory... This is my 3 season with the Livorsi setup.

Some small blocks have the oil psi sender just behind the intake manifold and in frt of the distributor. The intake almost touches where it is screwd into the block.

The later small blocks usuall have it here #17:

http://www.mercruiserparts.com/images/COMMON/9807.png

SB thank you for the pic!

I'll bet its as simple as a poor ground wire.....

Update this for the fix and problem. THX

Also asking does your oil pressure gauge increase sporadic (bouncing) readings while you trim the outdrive(s) If so then you have wiring problem of some sort. Grounds included to.

You are experiencing exactly what we went thru at the beginning of the season. Check every stinking ground. I guarantee that you have ground issues...we found corroded ground wires everywhere. A bit of time and patience and this is a very easy fix. Good luck. The beers will taste great when you are finished. :ernaehrung004:

I had a ground issue last year... I cleaned up the main harness and it was gone. It can be time consuming... But it's cheap!! LOL...I'm hoping its on the sender.

I hear you about bad or even loose connections even jumper in series from one gauge to the next being installed. Like I asked if your oil pressurereadings moves or drops when you use the trim - you have some sort of wire problem - resistance, corrosion or loose and or bad ground(s)

Make sure you don't have thread sealer on the sender. They ground through the body of the sender and thread sealer will compromise that ground.

One of my eng's did the same thing for 2 seasons- steady pressure at idle up to 4500 rpms then it would bounce around like crazy. Replaced sender and gauge- no change. Put a mechanical gauge on it and it was fine so I just lived with it. Last weekend I was working on some other issues and ended up moving around and disconnecting/ reconnecting several of the wiring harnesses. When I ran it after that, I had steady pressure for the first time in 2 years.