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2002 gmc envoy_sle
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Discussion Starter · #1 ·
Ok, I know much has been said about this but having a herd time figuring out what good pressure readings should be with this engine.
I have a test guage Installed and at 2500 have about 55psi 2000 have about 38 psi 1500 have 25psi 1000 have about 20. At idle it drops to about 8 which triggers the onboard dummy guage. Idle is 750ish at this point.

I dove to what I hoped would be the most likely issue, the oil pickup and seal. New seal and pickup clean.

Idle seems right from what I have read so have not done anything with the throttle body.

Fresh Mobile 1 5w-30 high mileage synthetic and Mobile 1 filter.

What things should I check before an oil pump replacement?

Plan on checking the pressure relief at the filter tomorrow morning.
 

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If I remember correctly, 8psi at idle is when the switch turns on. Before I tore into the engine, I'd try a new oil pressure switch, and check the oil filter. Try an A/C Delco.
 

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Discussion Starter · #3 ·
New oil filter. Funny reading through threads one says Mobile one another AcDelco ect.

Would be great to confirm with what GM says is proper oil pressure at idle. Thanks. Also heard it was 9psi that it activated.
 

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Discussion Starter · #4 ·
If I remember correctly, 8psi at idle is when the switch turns on. Before I tore into the engine, I'd try a new oil pressure switch, and check the oil filter. Try an A/C Delco.
So, friend had a envoy Hayes manual and found that lowest oil pressure at 1200RPM is 12psi. If,if, my vehicle tach is correct, I am well above that. So, in route to get a proper test tach and a oil pressure sensor. Will cost me a bit and $50 could be wasted if the sensor does not take care of it but better than a replacement engine or just getting rid of it for a $52,000 new truck
 

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One thing to remember is that in these engines, the 4.2 L Vortec, it is the volume of oil that is flowing through the engine that is the most important factor - not the oil pressure. Yes, there will be a necessary minimum oil pressure due to friction in order to get the oil flowing, but it's the amount of oil flowing that is important.

The oil pressure that is displayed on the instrument panel gauge is a "dummy" number that is generated by the PCM to keep people from freaking out. The best way to measure oil pressure is using a mechanical gauge.

Also, if your engine is not ticking, clanking or making other low oil noises, I would not get too concerned if you only measure say 8 psi at 1200 rpm as opposed to 10 psi at 1200 rpm.

For the oil pressure test, as far as which oil filter to use, I would use an ACDelco filter since that is what the factory used in the generation of their oil pressure @ whatever RPMs. The Mobil One filter (or any other manufacturer's filter) might be slightly more or less restrictive and throw the measurement off.
 

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Discussion Starter · #6 ·
One thing to remember is that in these engines, the 4.2 L Vortec, it is the volume of oil that is flowing through the engine that is the most important factor - not the oil pressure. Yes, there will be a necessary minimum oil pressure due to friction in order to get the oil flowing, but it's the amount of oil flowing that is important.

The oil pressure that is displayed on the instrument panel gauge is a "dummy" number that is generated by the PCM to keep people from freaking out. The best way to measure oil pressure is using a mechanical gauge.

Also, if your engine is not ticking, clanking or making other low oil noises, I would not get too concerned if you only measure say 8 psi at 1200 rpm as opposed to 10 psi at 1200 rpm.

For the oil pressure test, as far as which oil filter to use, I would use an ACDelco filter since that is what the factory used in the generation of their oil pressure @ whatever RPMs. The Mobil One filter (or any other manufacturer's filter) might be slightly more or less restrictive and throw the measurement off.
You must have missed that I am testing using a actual oil pressure test guage.

Anyhow, ac Delco filter, new sensor and still have needle fall off after a 20 minute drive at idle. Odd thing is I shut it down and restarted it after this started and let it idle for 10 minutes and had no needle drop. Obviously, it is not due to the engine heating and oil pressure dropping too low. Seems electrical in nature but very unsure what or where at this point. Going to install an permanent actual oil guage. Just wish there was a way to get the check guages light to stop for just the oil.

Also adding a little Lucas to it to bump the pressure up. Next oil change I will go with a slightly thicker oil.
 

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It could also be a flaky stepper motor on the instrument panel. They are known to go bad.

As far as going to a thicker oil when you next change the oil and filter, doing so risks degraded engine performance due to improper operation of the VVT solenoid due to the thicker oil. The VVT is oil pressure driven.
 

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Discussion Starter · #8 ·
It could also be a flaky stepper motor on the instrument panel. They are known to go bad.

As far as going to a thicker oil when you next change the oil and filter, doing so risks degraded engine performance due to improper operation of the VVT solenoid due to the thicker oil. The VVT is oil pressure driven.
would Not be going to anything much higher. I might just continue using Lucas. It has raised my oil pressure at running temp 2PSI which has now stopped the gauge from dropping and the check gauge light from coming on at idle after a longer drive.

You mentioned a bad stepper but just to be certain with what I expect a bad stepper should not cause the "check Gauges" light to illuminate correct?
 

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One thing that has not been asked is how many miles are on the engine?

By "dummy gauge" "check Gauges", etc., light to illuminate, I take it you are referring to the Check Engine light or the Service Engine Soon light.

I doubt that a bad stepper motor would cause the Check Engine Light or Service Engine Soon (two separate warning lights) to illuminate.

So confirming that you installed a new oil pressure sending unit and a new ACDelco oil filter, and assuming that the wiring is intact between the oil pressure sending unit and the PCM, the ground connection is clean and tight, the Check Engine Light does not come on, and the engine doesn't make and low engine oil sounds, I would consider things are OK.
 

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Discussion Starter · #10 ·
One thing that has not been asked is how many miles are on the engine?

By "dummy gauge" "check Gauges", etc., light to illuminate, I take it you are referring to the Check Engine light or the Service Engine Soon light.

I doubt that a bad stepper motor would cause the Check Engine Light or Service Engine Soon (two separate warning lights) to illuminate.

So confirming that you installed a new oil pressure sending unit and a new ACDelco oil filter, and assuming that the wiring is intact between the oil pressure sending unit and the PCM, the ground connection is clean and tight, the Check Engine Light does not come on, and the engine doesn't make and low engine oil sounds, I would consider things are OK.
02 Envoy SLE 220,000 and it has an actual "CHECK GAUGES" Light separate from the "Service Engine soon " and "CHECK ENGINE" light.

I am no longer worried about it really. According to my buddy who used to race Porches and the Hayes manual 12psi at 1200 RPM is minimum. Prior to even adding Lucas I had that 18PSI at 1200RPM now at 620ish I have 12PSI. I am going to just get a true Gauge and install that and if I have to pull the Bulb for the "Check Gauges" Light.

Might get under it and pull the sensor plug and take a picture so you can see the "Check Gauges" Light.
 

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Discussion Starter · #11 ·
One thing that has not been asked is how many miles are on the engine?

By "dummy gauge" "check Gauges", etc., light to illuminate, I take it you are referring to the Check Engine light or the Service Engine Soon light.

I doubt that a bad stepper motor would cause the Check Engine Light or Service Engine Soon (two separate warning lights) to illuminate.

So confirming that you installed a new oil pressure sending unit and a new ACDelco oil filter, and assuming that the wiring is intact between the oil pressure sending unit and the PCM, the ground connection is clean and tight, the Check Engine Light does not come on, and the engine doesn't make and low engine oil sounds, I would consider things are OK.
Actually, no need to here is someone on Redit that had the same problem and the video shows the light

Check Gauges light Video
 

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Thanks for the information. I learned something new today!

OK on the engine having 220K on it. I hope you get another 220K out of it before needing any other repairs.

Good Luck in your travels!
 

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Discussion Starter · #13 ·
Only need to get another year or two so no way near that milage. Putting Money away for a new truck. But need to have it running wife is itching to go camping/fishing and so am I.

Thanks for help people. But not totally finished here. Will let you know if I continue to have the gauge issue once I have reason to drive 20 minutes or more.
 
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