Do I need a new oil pump? 05 Silverado 5.3L

[relentless85]

I have been concerened with the oil pressure reading on the dash gauge since about a few weeks ago.  Short story is, i was driving on the highway, noticed a shuttering sound then a tick and tapping sound coming from the engine.  I pulled over, the engine was full of oil but i noticed the oil gauge on the dash was reading low.  Normally it reads 40+ all of the time.  It was lower than 40 almost to 20 PSI.  I connected a mechanical oil gauge to the engine and here are the results:

 

At cold start the mechanical gauge reads 44-45 PSI then after about 1:30 goes down to 41 PSI at idle. Here is a video of cold start to idle: https://youtu.be/VeBDv-LvV28

After the engine is up to operating temp and has been running for 15-20 minutes, the mechanical gauge reads 28 PSI and the gauge on the instrument panel reads in between 20-25 PSI at idle. Here is a video of the engine warmed up and running for about 15-20 mins https://youtu.be/PVsrAZWBZNM

Then I turned on the Air Conditioner. When the compressor came on the mechanical gauge started fluctuating as well as the instrument panel gauge. The panel gauge read a little below 20 and the mechanical gauge fluctuated between 25-28 PSI. When i turned the AC off, the mechanical gauge did not fluctuate any longer. Here is a video after the AC was turned on: https://youtu.be/Hsy2moas7ko

The parts that have been replaced so far are:
New oil pick up tube
New oil pick up tube 0-ring
New oil pressure sensor

 

Using Mobil-1 5W-30 and a Wix oil filter.

By watching these videos, would you say i need a new oil pump?

[Grumpy Bear]

You have allot of miles on this motor? 

 

Melling sells a higher volume pump for high mile motors. 

 

 

[relentless85]

7 hours ago, Grumpy Bear said:

You have allot of miles on this motor? 

 

Melling sells a higher volume pump for high mile motors. 

 

 

The engine has 146k miles on it. If I need to replace the oil pump, I was considering the Melling M295HV pump.

[Grumpy Bear]

Good choice. These are then Ecotec3 test pressure minimums. (below) Example only as I do not know nor have access to the Gen IV numbers but expect they are not much different. I could be wrong but someone here has that information. There is an 'Ask the GM Tech" forum as well for such information. 

 

https://www.gm-trucks.com/forums/forum/81-ask-the-gm-technician/

 

 

Hot oil pressure minimums.

22 psi @ 1,000 rpm

30 psi @ 2,000 rpm

33 psi @ 3,000 rpm

LV1, LV3, L83, L86 and L96.

[Brian715]

You shouldn't have an noise with 20psi. My 06 had 300,000 miles and wouldn't get over 20psi on the highway but never made a peep until you got to a light and the pressure went to 0. As soon as the pressure came up past 10psi all the noise would stop.  Might help but might not. 

[relentless85]

Well I went through the process of replacing the oil pump with a melling M295HV pump.  Now this is what I’m getting with a mechanical oil pump connected to a port just above the oil filter......After melling M295HV install

 

if you watch the video. The gauge needle flutter and fluctuates rapidly at idle and at higher rpms. 
 

Crank case is full with 6 quarts of oil. New wix oil filter. Engine was primed before starting by holding the gas pedal down and cranking engine 5–10 seconds at a time until I saw oil pressure at the mechanical gauge.

 

new oil pump, new pickup tube and o ring. New timing chain.

 

i am puzzled. I don’t think this is normal?

[CamGTP]

Did you happen to replace the camshaft retaining plate when you had the front cover off?

 

There is a giant oil seal all the way around on that plate. They go flat or could kinda blow out in one section. It can cause low oil pressure and maybe even that flutter you see. This is only a shotgun guess because you've done just about everything else.

[relentless85]

9 hours ago, CamGTP said:

Did you happen to replace the camshaft retaining plate when you had the front cover off?

 

 

There is a giant oil seal all the way around on that plate. They go flat or could kinda blow out in one section. It can cause low oil pressure and maybe even that flutter you see. This is only a shotgun guess because you've done just about everything else.

No, I did not replace that gasket or take off that plate.