Low Oil Pressure

HiOSilver

Original poster
Member
Jan 2, 2013
12
Hi Everyone,

I have a 2004 Envoy XUV SLT 4.2L 4WD that has recently started indicating low oil pressure. I bought the Envoy new and have always changed the oil on schedule with Moble1.

I've read several threads here about this problem and mine is just like the rest - it only occurs at idle after the vehicle has been driven more than 10 miles (so it's fully warmed up). The consensus seems to be that the problem is almost always caused by either the switch or the wiring. I replaced the pressure switch with the correct ACDelco replacement and still have the problem. My gut says the wiring is an unlikely culprit - the logic being that faulty wiring would cause an incorrect signal to be sent to the computer at any RPM, not just at idle. Am I off base here?

Which probably means that the issue is a failing oil pump. The local GMC dealer says that the book calls for 15.1 hours of shop time at $140/hour plus parts. When you add tax that's starting to look like a $3,000 repair on a vehicle that's probably only worth $2,500.

I love my Envoy! Does anyone have thoughts on a cause other than the oil pump (or something just as expensive)?

Chris
 

freddyboy61

Member
Dec 4, 2011
276
Just so you know, the oil pressure gauge does not actually indicate real oil pressure. The sensor is only a on/off switch. The PCM creates a phony reading on the gauge.
What do you mean by the gauge indicating a low oil pressure. Does it go to zero?
You should have the oil pressure verified by using a mechanical oil pressure gauge attached to the oil pressure switch port.
 
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Sparky

Member
Dec 4, 2011
12,927
First off it would be good to know your actual oil pressure. Screw in a mechanical pressure gauge (I'm not sure where the port is) and see what the real oil PSI is.

Then, if it is still low, change the oil filter. Might have a bad one.

How many miles?

*edit* freddy got to it first!
 

mrrsm

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Oct 22, 2015
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First obtain this Accel Auto-Meter Competition Instruments Part# 2268 Metric OPG Adapter:

https://www.summitracing.com/parts/ATM-2268/

This thing gets installed into the Oil Port located on the Passenger side of the Engine Block just above the Oil Filter Manifold after the removal of the Port Plug with an H-10 Hex Socket as shown on my Engine here:

GM42LOILPRESSUREPORT.jpg

...and then use an inexpensive Oil Pressure Tester Kit to attach to the Metric Adapter and then after snaking the long hose around the Passenger Side of the Hood, lay the Gauge onto the Windshield so as you raise and lower the Oil Pressure via the ACC Pedal, you can comfortably observe what the actual Oil Pressure Levels are at any given RPM:

https://www.amazon.com/dp/B00AUIZGIS/?tag=gmtnation-20
 
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HiOSilver

Original poster
Member
Jan 2, 2013
12
To everyone that contributed to this thread - thank you. You deserve some feedback on this problem and what I've done since the original post.

After towing my boat (small fiberglass bass boat - maybe 2500 lbs including trailer) for more than 10 miles, the oil pressure gauge would drop to zero at idle. It would pick back up the second you touched the throttle.

I took the Envoy to a GMC dealer and had them attach a mechanical gauge which they said never got below 25 lbs.. But they also said they were never able to reproduce the zero oil pressure indication on the dash gauge.

The dealer first told me that it's likely the pressure sending unit (and yes, I know it's just a switch). I explained that I had just replaced the switch with a new AC Delco part. They responded with Oh, then its a wiring problem. When I asked why that wouldn't give a false reading off idle they said Hmm, that's true, it must be the oil pressure regulator (I didn't know there was such a thing). They told me that if the spring in the regulator gets weak it can hang and cause the oil pressure to go to zero. They said it would require the removal of the oil pump which takes more than 15 hours of shop time at $140/hour plus parts, tax, etc.. Yikes!

It makes no economic sense to invest that much into the vehicle so I have replaced it with a vehicle that is better equipped to tow in the Arizona heat. I really loved the XUV and hated to see it go.

Thanks again to everyone here.
 
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bspurloc

Member
Dec 27, 2012
295
Most likely nothing was wrong with the car.
The oil pressure switches constantly go bad and then It seems either people dont clean the oil out of the connector or the connector gets messed up so they replace the wiring and connector. If you search advance auto etc for the oil switch you will see it also finds the connector and wiring.
I've replaced this on my daughters a few times. very annoying, just like all the other random things that go bad for no reason. random as in things that should not go bad.
 
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Locksmith

Member
Nov 19, 2017
76
Columbia,SC
I agree! Unless you hear typewriting (do the kids know what the heck I'm rambling about? LOL) I wouldn't worry about it. Look on YouTube and May03lt just posted a video on the oil pressure gauge! I recently bought the new, improved stepper motors for the instrument cluster and had them all soldered in by a local electronic repair shop for $40 bucks US currency. I watched enough YouTube vids to remove it ad the stepper motor seller even threw in a few bulbs for the instrument panel!
 
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signalnc

Member
Dec 28, 2012
249
Will the oil come out when changing the oil pressure switch? Does the oil need to be drained first? thanks
 

mrrsm

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Oct 22, 2015
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If you take a look at the image I modified and follow the natural path of the Engine Oil through the Oil Galleries leading from the Oil Pump and Oil Filter... upwards, into the Crankshaft Main/Con-Rod Bearings and Engine DOHC Valve Train ... the balance of the weightier, larger volume of Oil will be located well below this screw-in OPS component; settled down in the Crankcase-Oil Pan. While the Oil Galleries are fairly large and quite patent in this Motor...enough to move approximately 11 Gallons Per Minute at 65 PSI... when the Engine is at rest, it is the 'sticky' capillary action between the Engine Oil and the Oil Galleries that will hold (like a Soda Straw in a Milkshake) the relatively small amount of oil in them against Gravity for a little while as you work quickly to conduct the swap of the OPS. While Channel Locks can work to perform this R&R... the Proper Tool for this oddly shaped base of the GM Oil Pressure Sensor... is THIS one:

https://www.amazon.com/dp/B0002SR2RY/?tag=gmtnation-20

If you are that concerned about the Oil loss during the job ... a quick Dip Stick view before you begin ...and then after the OPS swap ...with the Truck down on a level surface, will let you know how much Oil to put back in. The Best Technique is to have the Old OPS loosened first... but not completely pulled out yet... while having the New OPS rigged and ready with a Brand New "O" Ring or Copper Sealing Washer. Then just unwind-rewind fast between the Old One for the New One... but not carelessly, mind you... lest you "wind" up stripping out the OPS threaded female port in the LL8 Aluminum Engine Block... DO NOT OVER-TIGHTEN THE OPS... It is the "O" Ring that performs the Sealing here... NOT the strength of your Torque! Just Tight.... Is Tight Enough:

GM42LOILPATH.jpg
 
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Redbeard

Member
Jan 26, 2013
3,466
It's been a couple of years since I changed mine out and don't recall but maybe a couple of drops coming out. As
MRRSM suggests just have the new one in place ready to install before you have the old one out. You won't have any problems with it. (Oil will only come out if you try to do this change while the engine is running and for that reason it is not suggested.)
 
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