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LS4 Oil Pressure Dilemma

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bocoogto

New member
My 2008 GXP intermittently shows Service Engine light. Code is due to oil pressure sensor malfunction. I put a gauge in place today and saw 40 psi at startup, which dropped to about 15 psi within a few minutes as the engine warmed. A fairly loud lifter tick showed up when the pressure was low. I took the car for a drive--about 10 miles--and rechecked the gauge. After thorough warmup, oil pressure now shows 35-40 psi at idle.

I thought the gage might be stuck, so I shut the engine down and it drops immediately to zero. Startup still shows 35-40 psi at idle.

Engine has 165,000 miles on it. Oil now in the engine is 5w-30. Filter is AC PF63. Oil consumption is about a quart per 1,200 miles.

Is there an explanation for the oil pressure variation as I described? Why does a hot engine show more oil pressure at idle than when first starting the engine?
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I've got a theory of why the oil pressure was first 15 psi at idle and now consistently 35-40 psi at idle.

The screen under the pressure sensor may have been fouled, preventing full pressure from reaching the gauge. In the 48" of plastic tubing from the engine to the gauge, there is about 15" of oil that is visible in the tubing. It looks quite dark.

Even though I changed this screen last year when changing the sensor, it may be that particles from the oil passage partially blocked flow. Could that cause the lifter tick, also?

I will remove the screen to check it when I remove the gsuge fitting and re-install the sensor.

That's the best explanation I can come up with now, but would like to hear your opinion.
 
Low oil pressure does cause lifter tick because the lifters aren't fully pumped up and that leaves play.

How often do you change the oil?
 
Yes, 15 psi oil pressure does cause lifter tick. My question is what could cause low oil pressure on a cold engine vs. normal 35-4- psi at idle when hot.

Can the screen below the oil pressure sensor cause a low reading AND restrict oil to the lifters?

I change oil every 5,000 miles. 5W30 Synthetic Quaker State. AC PF63 oil filter.
 
I would try adding some marvel mystery oil or sea foam to try cleaning up any gunk in the top end. the DOD solenoids in the valley cover have small passages that could be gunked up. If that doesnt work than it may be time to replace or delete the DOD parts.
 
Changed oil yesterday. Quaker 5W-30 full synthetic with AC PF63 filter. Initial starup at idle--10-15 psi. AFter idling 10 minutes, oil pressure climbed to 30 psi.

I removed the screen below the oil pressure sensor and noted that it is clean, so I reinstalled it and did the starup as described above.

I've noticed previously that oil pressure does rise from 10-15 psi to 40 psi at about 1000 rpm.

Very puzzling.
 


Oil pressure problem remains the same. Cold startup pressure at idle is 10-15 psi. Lifters sometimes clatter. After 10 minutes of idling, pressure goes to 25 psi, lifters are quiet. Anytime the engine is revved beyond 1500 rpm, pressure goes to 40+ psi.

Every engine with oil pressure problems got worse as engine warmed up. This is puzzling.

I changed the oil (Quaker 5W30 full synthetic and AC PF63 filter), added 6 ounces of SeaFoam to the oil after reading that some people get "magic" results. We'll see what happens.

A side benefit of unplugging the sensor wires is that the shudder when stopping has gone away completely. As some have told me, the problem is the DOD staying in 4 cyl. mode when stopping. Problem is, the Service Engine Soon light stays on and remote start won't work.
 
At some point you may have to really tear into it.

Like oil pump and pick up tube 0-ring type issues. Maybe even the oil pressure relief valve is sticking, bleeding off lots of oil pressure.
 
bocoogto said:
Oil pressure problem remains the same. Cold startup pressure at idle is 10-15 psi. Lifters sometimes clatter. After 10 minutes of idling, pressure goes to 25 psi, lifters are quiet. Anytime the engine is revved beyond 1500 rpm, pressure goes to 40+ psi.

Every engine with oil pressure problems got worse as engine warmed up. This is puzzling.

I changed the oil (Quaker 5W30 full synthetic and AC PF63 filter), added 6 ounces of SeaFoam to the oil after reading that some people get "magic" results. We'll see what happens.

A side benefit of unplugging the sensor wires is that the shudder when stopping has gone away completely. As some have told me, the problem is the DOD staying in 4 cyl. mode when stopping. Problem is, the Service Engine Soon light stays on and remote start won't work.
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Have you replaced the sensor? The filter can be cleaned with gas but they are cheap so I just replaced mine when I did my sensor. 5w-30 is fairly thin oil, and your mileage is up there. Might want to run something thicker. Motor Medic makes a good motor flush used at oil change for higher mileage engines, I have seen results in the past using it. If you havn't owned the car since new it may not have been cared for as it should have been, and DOD is a dirty system as well. Aside from dropping the pan for the o ring and revised gasket not much you can do without getting dirty. Good luck.
 
I replaced the sensor and screen and still get the Service Engine Soon light intermittently. The screen was not dirty. Then, I put a gauge in place of the sensor and found that, with a cold engine, oil pressure is indeed low at idle--about 10-15 psi. After 10 minutes of idling, the pressure builds to 30 psi at idle. I had already tried 10W-30 oil before changing the sensor. It did not improve the situation. In fact, the symptoms indicate thinner (hot) oil results in higher pressure.

We'll see if the SeaFoam helps--if the intake screen is partially plugged.
 


Don't remember the numbers, but it said "Oil Pressure Sensor malfunction." Based on what the gauge shows, this was a legit code to display. 10 psi at idle is too low. Service Engine Light comes on when the engine is cold at idle only. If I reset it, it comes on only the next time the engine is cold.
 
So, the oil pressure problem has gotten better since I added Seafoam in the oil. Also, I've noticed that when the oil pressure sensor plug is pulled, the shudder when stopping is completely gone. But, the Service Engine light is always on. I realize the DOD is disabled with the sensor disconnected, which is why the shudder is gone. How can I restore the oil pressure monitoring and keep the DOD turned off?
 
you need a tune to turn off the DOD. i think it might new lifter time for you. the dod uses the lifters to work the DOD. turning it off makes the lifters stay full i suppose.

there maybe a odb2 plug in like "pedal commander", for the gxp. might do the dod disable too. not 100% sure if they make one for your car tho, just know they are out there.
 
If removing the oil pressure sensor plug disables DOD, isn't there a way with the three wires to that plug to disable DOD, but still monitor oil pressure?
 


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