Oil pressure low - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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  #1  
Old 05-06-2009, 06:42 PM
mbergh mbergh is offline
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2002 Olds Bravada
Pewter Metallic 4.2L I6 4X4
Join Date: May 2009
Location: Aurora, IL
Posts: 38
Oil pressure low

2002 Bravada w/120,000 miles...all good until recent oil pressure problem. Starts OK and drives awhile locally w/no pressure problem after warm-up. Eventually, when stopped @ idle (600 RPM) the oil gauge pressure drops off fast and "check gauges" light comes on followed by "Low Oil Pressure" readout and then "Stop Engine". If I give it a little throttle (to 700-800 RPM) the pressure comes back to 45-50. I had the oil pressure sensor replaced, no oil burning or leaks. Had mechanic look at it and he changed the oil and added an oil treatment. Has made no difference. It does not knock when pressure drops off although I do not let it stay there. It does shut down hard when I'm done driving. Recently, I noticed that when I try to idle at 700-800 RPM the idle lopes. I've read that it could be the oil pickup, oil pump, main bearings...etc. But it makes no sense to me as I've driven the SUV for 20-30 min in local traffic and it's fine. Due to the loping idle I added fuel injector cleaner and cleaned the throttle body. I am totally frustrated and no one can give me an answer. I do not believe the main bearings are shot as I religiously change the oil and never muscle the car. If it was the bearings it would have a more consistent pressure problem. After all, the oil is hot after 10 minutes and does not lose its viscosity. HELP!
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  #2  
Old 05-06-2009, 07:25 PM
fifields fifields is offline
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2007 Chevy TrailBlazer LS
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Off the top of my head it could be sludge in the bottom of the oil pan restricting the pick-up toob or the screen on the pick-up tube is plugged. And last but not least, is it possible that a piece of the "plastic" seal on the top of one of those oil bottle, oil treatment etc. fell into the oil pan??? It could explain the erratic drop in oil preasure. Does it go away after the engine is shut down for a minute or two??
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  #3  
Old 05-06-2009, 07:33 PM
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Super 88 Super 88 is offline
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First off, let's remember that on the I6 the numbers on the oil pressure gauge means NOTHING! Any number on the dial only means there is more than 12 psi.

I'm still wondering if the sensor is bad (I know he said he replaced it already) - or the wiring to the sensor is bad. I would start by begging, borrowing or buying a real oil pressure gauge and see what the actual pressure is!
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Old 05-06-2009, 07:37 PM
mbergh mbergh is offline
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2002 Olds Bravada
Pewter Metallic 4.2L I6 4X4
Join Date: May 2009
Location: Aurora, IL
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Oil Pressure Low

I'm hoping it's the oil pickup. I do not think the mechanic tested the oil pressure manually or pulled the oil pan to check the oil pickup. However, I doubt anything went into the oil pan as it was doing it before the additive. After it starts acting up and I shut the engine down it will continue to do it if I restart it right away. Only after it sits a while and gets cooler does the problem go away.
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  #5  
Old 05-06-2009, 07:45 PM
mbergh mbergh is offline
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2002 Olds Bravada
Pewter Metallic 4.2L I6 4X4
Join Date: May 2009
Location: Aurora, IL
Posts: 38
Oil Pressure Low

Super88 has a point. It gets frustrating as everytime I take the SUV to a mechanic it costs me money even if it's not fixed. Seems they like to experiment with the problem at my expense. One would think he would have used a mechanical gauge, tested the sensor and checked the oil sump tube. I told him to drive the car on the expressway and get it warm and take it back to the shop. That's when the oil pressure gauge reflects a sudden drop-off in pressure. He stated he ran it for 25 minutes and then tested it but I've run it for 30 min in the driveway and the pressure does not drop off. Many mechanics are bozos and live by the fact that there is more money in not solving the problem. Taking it to thr dealer is a trip nowadays as many run up your bill to compensate for not selling cars. I experienced this in Las Vegas before I relocated back to Illinois in January of this year. However, all this does not explain the RPM loping and hard shut-off after the gauge starts reflecting the pressure problem.
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  #6  
Old 01-20-2010, 12:26 PM
mbergh mbergh is offline
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2002 Olds Bravada
Pewter Metallic 4.2L I6 4X4
Join Date: May 2009
Location: Aurora, IL
Posts: 38
oil pressure low

Just to close this out- the problem was a leaking vacuum cap on the intake manifold. After warmed up and returning to idle, the vacuum would drop and send a signal to the PCM that the vehicle was shutting off. Therefore, the pressure would drop. It very well could damage the engine so it's well worth the $0.50 part.........
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  #7  
Old 01-20-2010, 12:36 PM
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christo829 christo829 is offline
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Might want to mark this as "Solved", but thanks for following up! It's
little items like that that can create big headaches. There were a
couple of other members who had oil pressure problems. Wonder if
it could be the same issue?

Glad you found the solution!

Cheers-

Chris
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  #8  
Old 01-20-2010, 08:54 PM
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rrufast rrufast is offline
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Can you take a picture of the cap that was leaking? I'm interested to see what was causing the problem...
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  #9  
Old 01-21-2010, 02:19 AM
WOOLUF1952 WOOLUF1952 is offline
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  #10  
Old 01-25-2010, 02:33 PM
mbergh mbergh is offline
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2002 Olds Bravada
Pewter Metallic 4.2L I6 4X4
Join Date: May 2009
Location: Aurora, IL
Posts: 38
oil pressure low

Unfortunately I put everything back together so I do not have a photo. On my Bravada the top of the engine has an airbox which is attached to the throttle body. if you take this off it exposes the intake manifold (a large oblong metal cannister on the drivers side of the engine. On the top of the intake manifold is a vacuum fitting with a flat ended cap. it is the only one there so it's easy to locate- it is towards the front of the intake manifold. Anyway. it gets old, hard and cracks due to its location on the top of the engine. I'm sure it did not help that I lived in Las Vegas from 2002-2008 and the dry heat contributed to its dryrot. i did not notice it before because the crak was on the bottom of the cap. Only when I rotated it did I see it was cracked and leaking. When replaced, the engine ran smoother and no oil pressure drop.
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