Low oil pressure GQ 2.8td

[Shadow121111]

Hey guys

my 2.8 gq has suddenly started running with low oil pressure, under 5psi at idle unless revs turned up, gets to 20psi when driving around, then drops back to under 5 after a few seconds.
before it was running around 15psi at idle and up to 80psi when driving, I have an after market gauge fitted for oil pressure and have changed the sender unit to confirm it wasn't the problem
I have noticed recently there is a slight tapping sound from the top end which is a worry.

Strange thing is it runs really well, turbo runs at 13psi, not overheating, still pulls trailers up hills, etc.
I have changed oil and filter today as that had been suggested as a cause (unlikely as i do changes every 5000) but the problem still remains.
I am now not to sure what to check next

Any Ideas would be greatly appreciated. Cheers

[Shadow121111]

Would it be worth pulling the front off and checking the oil pump, or is it more likely to be elsewhere in the engine

Thanks

[threedogs]

Doesn't the sender unit have to have the same OHM value as the gauge.
Could be wrong but all I can think of ATM

[Shadow121111]

yes that is true, i have the standard oil pressure gauge in the side of the block and a tee coming off the oil filter housing for the aftermarket gauge, i replaced the aftermarket sensor and it was still reading the same.
both gauges read low the one in the dash takes a long time to react though thats why I put an aftermarket one on (all installed 2 years ago so no issues with fitment)

[Shadow121111]

Pretty sure I noticed the oil pressure was overly high (on the gauge) a while ago, checked everything, all looked ok, thought maybe faulty sensor (replaced sensor since, no change), now it has gone to low pressure. Could this mean something?

[threedogs]

I take it these are mechanical gauges as in a hose going to each,
I'd be looking for air leaks or loose fittings before I start pulling things apart
If not mechanical I'd look at a faulty earth strap , or maybe make a new one and fit it

[Shadow121111]

first one was electronic, 2nd one was mechanical, still reads the same either way, starting to think it may be the oil regulator or bypass valves

[Shadow121111]

Checked old earth straps (Checked ok) and ran new earth straps 1 to engine, 1 to chassis - no difference. Could find no air leaks or vacuum leaks, pulled sump off checked oil pump relief valve - looks fine. not too sure what else to check.

[threedogs]

std clearance on the oil regulator valve is .040 to .097mm if not replace