P0521 cured - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 5.3L V8 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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Old 06-11-2019, 09:34 AM
Pat80flh Pat80flh is offline
Junior Member
Join Date: Apr 2019
Posts: 4
P0521 cured

I replaced my cam and lifters, deleted AFM, had the ECM reflashed, and replaced the oil pump with a Melling. Got it all together ran great, no noise, solid and immediate oil pressure. BUT, during the first 1000 miles, I was getting an intermittent P0521, oil pressure out of range. There was no rhyme or reason, it happened once within 30 feet of leaving driveway on a cold start, other times 100 miles into a long drive. Gauge always showed good oil pressure for what it's worth(nothing). No noise, crankcase full, no other symptoms of low oil pressure.

It worried me, an oil pressure problem is not something I'll ignore. I racked my brain, trying to come up with a plan to diagnose it that did not include pulling the oil pan/diff again. The randomness of the failure is what puzzled me, not your usual low pressure at idle problem, it almost always occurred at speed. I finally decided to dump the conventional oil early and put some synthetic in there, something I planned to do after the first 1000 miles. So off to the zone I went. When I purchased the rig, there was a nice new Fram filter in the front seat which I happily used, my parts bill was getting out of control. But as I looked through the catalog, I saw the Delco filter listing contained a note ,PF46E contains a built in check valve. I opened up a Delco filter box, looks like a regular oil filter. I opened a Fram and an STP filter, both had a large rubber flap that looks like it was designed for anti-drainback. I bought the Delco anyway and guess what, problem solved. The girl behind the counter was trying to talk me out of the Delco filter because there was a special on oil/filter combos and the Delco was twice the price.

You can't put a price on peace of mind.
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Old 06-11-2019, 12:36 PM
mddombrowski mddombrowski is offline
2006 Chevy TrailBlazer LT EXT
Summit White 4.2L I6 4X4
Join Date: Jan 2017
Location: Charlotte, NC
Posts: 195
When all else fails... go to the OEM. I use Fram because I like the grippy stuff they coat the filter with, but I only use their premium filter, not the standard orange one.
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Old 06-12-2019, 08:20 PM
suzieq suzieq is offline
Junior Member
Join Date: Aug 2018
Posts: 6
Stay with OEM delco filter, never had anything but problems with fram filters.
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Old 06-14-2019, 10:12 AM
TB-Al's Avatar
TB-Al TB-Al is offline
New Member
2007 Chevy TrailBlazer LS
Graystone Metallic 4.2L I6 2WD
Join Date: Nov 2017
Location: Pleasure Island, Al.
Posts: 338
Bob is the oil guy is the best place to get oil and filter answers. https://www.bobistheoilguy.com/ Years ago he had a test of many different oil filters. Used them a while and then cut them apart to see how they were made and how they performed. Fram was the absolute worse. Fram oil filters are also known to come apart under pressure. Cheap filter material and cheap cardboard where others use metal. I've used Wix for many years but would not have a problem with OEM. GM does know what they are doing most of the time.
"It is useless to do with more what can be done with less." William of Occam
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