Just put a new 496 stoker in my boat. Everything has been running well. Was out twice with no issues. Went out this evening and the oil pressure readings are screwy. Start and idle reads normal. When i start running it drops down to zero, like it is not reading anything. At around 4,000 RPMs or so, it will start flickering from zero up to 60 and drop to zero again. Will just sit at zero then. Drop back down to idle and gauge reads pressure again.

What should I look at for a possible cause. Everything on the engine should be new. Any feedback?

Wire making a bad connection to the sending unit or the sending unit it self is bad. First thing I would check.

Do not use any sealer on the sending unit when you screw it into the block. It keeps the sender from grounding.

If it was a ground issue...then why would it return as soon as he gets back to idle ? He says he has nothing at 4000 rpm. You guys may be right...but it sounds to me like the pickup came off the oil pump.

Definitely try a new sender first tho...it's the cheapest.

screw a mechanical gauge into it ASAP to make sure you really have oil pressure before you cook a motor. provided the mechanical shows everything all good then you can go through the wires, you could have a flaky sending unit or gauge, rubbed through wire someplace, maybe a loose wire in your dash panel, all sorts of possibilites.

just rule out actual oil pressure issues with the mech gauge first and go from there.

my last baja had a flaky oil pressure gauge, 9 out of 10 starts it read fine, the 10th it would show ZERO pressure, after verifying i had oil pressure i ended up just carrying a jumper wire and simply jumped neg battery to the oil pressure sender and the gauge would spike to max oil pressure as soon as i remove the jumper then the gauge would go back to 50-60psi like it usually was. why that gauge liked to stick i have no idea why!

Is your alarm going off, it uses a different sender.

Alarm is not going off, but I am not sure the alarm is hooked up now, as it does not sound when I turn the key to the power on position, which it did with the last engine. Was in it messing around with the wires etc. The way the oil pressure sending unit is set up, it comes out of the engine and is connected to a T type fitting. The oil pressure sending unit is on one side and some other fitting with two wires is on the other side of the T.

When the power is off, the pressure reads between 20-40. Start it up and it goes to 50-60. Review to about 1,000 and it drops to zero. Drop back down to idle and it flickers between 0 and 60. When revving the engine, it will flicker between 0-80. I can't tell if I have more blow by or not. If I stop and restart and stay at idle, it will stay between 50-60.

When I stop the engine and check the oil, the oil is really low, so seems like the oil is getting up into the engine. After a couple minutes all he oil is back in the pan.

helpful advice # 56 ... revving the motor when you suspect no oil pressure is NOT the gold standard for diagnostics...

i have mecanical guage for oil pressure and water temp, to have a second instant diagnostic of my readings in case the dash gauge comes fuzzy...

Just another random thought....you ARE using the correct dipstick right ? And....there is roughly 6-7 quarts of oil in it right ? Are you sure ?

(Not doubting your abilities...but I've seen people do worse to their motors sir. )