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Author Topic: 2009 wouldn't start, now it loses oil pressure  (Read 114 times)

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accelerator

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2009 wouldn't start, now it loses oil pressure
« on: January 12, 2020, 12:47:53 PM »

I'm hoping you guys can help me out with my 2009 Avalanche LTZ 5.3 w/ 141000 miles.  Up until a few days ago the motor was running fine.  Then yesterday the engine would turn over, but wouldn't start.  Occasionally I could hear a cylinder fire, and I could smell fuel in the exhaust, but it wouldn't run.  After messing around I got it to start after giving it a little bit of throttle.  After that I figured maybe the throttle body was dirty, so I gave it a thorough cleaning, and now it starts every time.

But now I have a new problem!  The oil pressure is 40 psi when I first start it, but after a minute it will slowly drop down to zero and the alarm will come on.  I let it run for a minute with no oil pressure, and the engine seems to run fine with no weird sounds or vibration.  I know the oil pressure sending unit is a common issue, but would that be related to the no start?

Also, in looking around the engine bay it seems like there is a small oil leak near the exhaust manifold for cylinder 4/6, right near the dipstick. I can see a spot of oil on the manifold itself, and it smokes a bit.  I never noticed a burning oil smell when driving before, so could this be related to either of the above issues?

At this point I'm kinda stumped, and just want to get this fixed so I can sell my Av.  I love the way it looks and rides, and I love the cargo space, but it's been nothing but trouble for the 2.5 years I've owned it.

Thanks in advance.

edit: I should add there are no codes
« Last Edit: January 12, 2020, 13:05:02 PM by accelerator »
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BainMan

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Re: 2009 wouldn't start, now it loses oil pressure
« Reply #1 on: January 13, 2020, 07:42:38 AM »

Hey accelerator. Let's start off simple, does it have oil? What reading do you get on the dipstick? How many miles since last change?

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2010 LTZ, bone stock 5.3

accelerator

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Re: 2009 wouldn't start, now it loses oil pressure
« Reply #2 on: January 13, 2020, 08:46:11 AM »

Dipstick shows the oil level is fine, just changed it about a month ago.
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BainMan

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Re: 2009 wouldn't start, now it loses oil pressure
« Reply #3 on: January 13, 2020, 09:12:28 AM »

Test oil pressure with a gauge set is what I'd want to do next: Cheap option from Harbor Freight

https://www.harborfreight.com/Engine-Oil-Pressure-Test-Kit-62621.html

The small leak on the manifold is likely just a valve cover gasket, probably not related. Strange there are zero error codes, have you scanned it with a tool for pending codes?
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2010 LTZ, bone stock 5.3

accelerator

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Re: 2009 wouldn't start, now it loses oil pressure
« Reply #4 on: January 13, 2020, 14:53:12 PM »

I scanned it with a Bluedriver scan tool, and it showed no pending codes.

Tried messing with it some more this afternoon.  It takes about 5 minutes for the oil pressure to drop.  I tried giving it some throttle, and that made the pressure go back up.  However when I let off the gas, the rpm's remained around 2000-2500 rpm and wouldn't go down.  Normally you would think vacuum leak, except it idles fine and my scan tool shows 20 inHg of vacuum at idle.

I'll probably just have it towed to the stealership tomorrow and let them figure this out.
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accelerator

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Re: 2009 wouldn't start, now it loses oil pressure
« Reply #5 on: January 14, 2020, 23:03:06 PM »

Changed the oil pressure sending unit yesterday, and it still has the same issues. Had it towed to the dealership, so we'll see what they say.
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