NEED HELP 5.3 rebuild

Skeesh

Original poster
Member
Dec 16, 2020
1
Oklahoma
So long story short had my 08 Sierra 5.3 rebuilt on drivers side because of number 1 cylinder. Been driving her since 12/4/20 and then this morning 12/16/20 I'm on my way to work 20ish miles or so mostly highway I pull into work and my oil pressure light comes on. So I kill it go to work. About 3 pm I go out to go do my grocery pick up with no problems. Leave work at 5. Get off on my exit few miles later turn into drive. Oil pressure light comes on. Any thoughts? Will be calling the place I had it rebuilt but just like to kinda troubleshoot before hand.
 

Mike534x

Member
Apr 9, 2012
894
How many miles are on your truck? and was it all the lifters on the drivers side, or just the single lifter that was replaced? And does your engine make any additional noises/sounds when the gauge is showing 0?


It could be a number of things, but there could be a chance the oil sensor filter is plugged. At the back of the intake on the engine block is the oil pressure sensor. There is a tiny plastic filter with mesh screens (can be removed once the sensor is removed, with the use of a pick tool), that sometimes get gummed up with crude/sludge in the oil. Sometimes it'll cause a low pressure reading if its blocked. If it wasn't damaged on removal, you can just clean it and put it back in. But if you don't have sounds like its starved of oil pressure, it could be a faulty sensor too. Best way would be to check that filter, and rent one of those oil gauges to manually check the pressure just to see if the sensor is faulty too.
 

mrrsm

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Oct 22, 2015
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Welcome to GMT Nation...

Just to cover all of the possibilities visually including those mentioned above, these are the Failure Modes...One is just a Nuisance...the others may presage a Catastrophic Engine Demise at Higher RPM.if either one or more of them are involved alone ...or simultaneously:

(1) Clogged Up Oil Pressure Sensor Screen: This is One PITA problem, but innocuos and quite common as well. There are quite a few YT Videos showing how to R&R the Oil Pressure Sensor along with its HIDDEN Replaceable S/S Screen from the Firewall area on the back Driver's Side of the Motor. A Mal-Installed or Loose Oil Pressure Sensor Connector or a Damaged OP Sensor Harness will throw Sketchy Readings on the IPC Oil Pressure Dash Gauge, too:

This is just a GENERIC Oil Pressure Sensor to provide the Part #s...Choose ACDelco:
GENERICOILPRESSURESENSOR.jpg
(2) Failed Oil Pump "O" Ring Pick Up Tube Seal: This "O" Ring comes in MANY varieties depending upon which type of LS Engine Series you have and generally requires More Labor to remove the Oil Pan to access the Oil Pick Up Screen and get to the underside of the Gerotor Oil Pump to unbolt the Tube Flange. A Perfect Vacuum needs to be maintained leading from the Base of the LS Gerotor Oil Pump to where the Oil in the Bottom of the Crankcase is suctioned upwards into the Oil Pump. If the "O" Ring Seal is Lost either due to a Cut, Sliced, Crushed or Flattened Out "O" Ring ...Air can be drawn into the Oil Pump and Defeat Oil Pressure. Air is easily compressed... But All Liquids are In-compressible.

LSOILPICKTUBEINSERTS.jpgLSTHICKERGREENORING.jpg

(3) Completely Clogged Oil Pick Up Tube Screen; Old Carbon Deposits in Chunks and Gas Gum Varnish from Cylinder Blow-By can collect on the Oil Pump Pick Up Tube Screen and occlude the Oil from passing through with enough VOLUME to Feed the Oiling System. These Chunks and This Junk can grow large enough to stop the Ingestion of the Oil from the Bottom of the Crankcase Reservoir. This can also occur if Engines are left sitting for weeks on end without being Started and Warmed Up often enough and reduce the Gas Gum from congealing down inside the Oil onto Engine Surfaces.

CLOGGEDOILPUMPICKUPSCREEN.jpg

If you have ANY Doubts about the condition of the LS Oiling System inside of your Engine, THESE Steps are Doable for us ALL to be able to Thoroughly TEST the LS Oiling System:

(A) First, locate the Oil Gallery Access Port of the Lower Left Side of the LS Engine Block. It will require either an H-8 or an H-10 3/8" Hex Socket to CAREFULLY remove this Plug:

LSENGINEHEXPLUGGEDOILGALLERY.jpgLOWERLEFTOILGALLERYPLUG.jpgLOWERLEFTOILGALLERYPLUG2.jpg

(B) Obtain an M16X1.5 to NPT Oil Line Adapter:

https://www.amazon.com/dp/B0894LDF76/?tag=gmtnation-20

LSENGINEMETRICTONPTADAPTER.jpg

(C) Obtain a Decent Analog Oil Pressure Test Kit:



ANALOGOILPRESSURETESTRIG.jpg

(D) Check the Engine Oil Level FIRST and ADD Oil as needed. Then after removing the Hex Plug, Install the M16X1.5 to NPT Adapter AFTER wrapping some Teflon Tape around the Male Threads and slipping the Sealing Washer onto the Adapter. DO NOT USE EXCESSIVE FORCE TO INSTALL THIS THING INTO THE ENGINE BLOCK.

(E) Then Thread the Male 1/4" NPT End of the Oil Pressure Test Kit Hose into the Female portion of the Oil Gallery Plug Adapter after wrapping Teflon Tape around the Threads. Again....DO NOT OVER-TIGHTEN THE HOSE FITTING INTO THE ADAPTER.

(F) Adjust the position of the Analog Oil Pressure Gauge along the length of the Oil Pressure Test Hose around the Engine compartment and Hood and place it near the Windshield so it can clearly be seen by anyone sitting behind the Steering Wheel.

(G) Start the Engine, without RACING the Motor above the Normal RPM level at Idle and Observe the Dial on the Gauge. Double check your Service Manual ahead of time and NOTE what the Nominal Oil Pressure should be for your particular LS Engine. IF THE OIL PRESSURE ON THAT TEST GAUGE DOES NOT RISE TO THE NOMINAL PSI LEVEL...SHUT DOWN THE MOTOR.

(H) If the Oil Pressure RISES and remains at NOMINAL, compare what you see on the Analog Test Gauge versus what the Dashboard Oil Pressure Gauge shows to determine if they reconcile and make sense. If the Dash Gauge goes 'in and out', Replacing the Oil Pressure Sensor and S/S Filter Screen Unit from the Back Driver's Side of the Engine Block is your next step.

Using the Analog Oil Pressure Test Gauge Method provides TRUTH and Definitive PROOF of the General Overall Health and condition of the Oiling System and Engine Bearings Nominal Clearances inside your LS Engine.

If the Oil Pick Up Tube Screen is CLOGGED, then the Oil Pressure Gauge Readings will likely Start LOW and Remain LOW throughout ALL RPM Ranges (Avoid Elevating the Engine RPM if you see Very Low Oil Pressure).

The additional problem of having a Compromised "O" Ring is the other possibility ...or BOTH conditions can be present on High Mileage Engines. In either case, ALL of these conditions can be rectified if necessary at the same time if conditions demand the R&R of the Crankcase-Oil Pan to gain access and affect repairs.
 

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Reprise

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A couple of thoughts from my end, since I've been here recently (not with 'zero' pressure, but from a disassembled (Gen3) engine due to freshening it up.)

The screen is a fairly common issue. And as was mentioned, this is pretty innocuous. You still have pressure; it's just that the oil can't get to the sensor.

I prefer the Teflon 'goop' (usually white), vs. the tape on that fitting, especially when it comes time to permanently re-install it back in place. If you're using the tape, only put it on the first few threads nearest the plug end, so that none of it breaks off & gets distributed through the engine.

You mentioned that the engine was just rebuilt. Hearing that scares me a bit, because of the things @MRRSM mentioned about the pickup tube connection. See the three different flanges in his picture? There are different o-rings to use, depending on the flange type. Hopefully, they (a): Used the 'correct' one, and (b): Installed it properly.
If it's wrong, usually you'll see 'zero' pressure on the first start (and it really *is* zero, too, so shut it down immediately). Hopefully, this isn't the issue with yours. We'll come back to this in a minute.

If you can, crank the engine without actually starting it, with the test gauge connected. See if it builds any pressure at all. Note that the crank bearings will float in oil with as little as 4psi of pressure, so if you get *low* pressure (like 10psi), you're still safe. GM's spec for the LS is minimum 6psi for each 1000rpm; 10psi per is considered adequate, and if your engine was registering more than this before it was rebuilt, it should *at least* have that same pressure, after rebuild. Especially if a new oil pump was put in, or even better, a high-volume and/or high-pressure pump. With the Gen 4 engines, a high-volume pump was OEM, btw (due to the AFM lifters, etc.)

If you have absolutely *no* pressure at crank (you won't have full or close to it, because the starter alone can't fully pressurize the engine), you need to decide if you want to start the engine or just have it taken to the rebuilder, at that point. If you start the engine, you should have immediate oil pressure. Don't rev the engine. If the gauge shows zero (and the DIC shows 'low oil pressure', if you have the DIC display)... shut it down. It will only take a few seconds to trash the crank bearings & damage the crank journals soon after.

As was mentioned... to check on the o-ring for the pump / tube requires the pan to come off - not just for the pump side connection, but to undo the retaining nuts that hold the tube to the engine (just below the windage tray). Because the tube isn't going to move very much without those nuts being at least loosened, if not removed. Well... it'll move if you *force* it, but that likely bends the tube. The other way to get the o-ring replaced would be to remove the pump (which is a front cover removal, and then the pump has to be aligned when reinstalling it, as well as installing a new front cover seal (and making sure *that* lines up perfectly, as well.)

For this reason, I would not try diagnosing the o-ring connection, myself, if I had just had the engine professionally rebuilt. Bring it to the shop, explain that you have *no* oil pressure, and let *them* repair it properly. That's why you paid them to do the job, of course, and if you go tearing the engine down yourself, you may 'void' whatever 'warranty' they provided.

Good luck to you, and let us know the outcome. Our collective fingers will be crossed 🤞
 

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