Misfire, low oil pressure, low RPMs

EDWOOOO

MEMBER
2005 GMC SIERRA
5.3L
V8
4WD
AUTOMATIC
156,000 MILES

I purchased this truck 4 months ago.
Noticed oil pressure drop gradually down to 17 over 1 month time. Mechanic removed oil pan, found sludge, cleaned it, pickup tube O-ring changed(different color).
Made no difference. Valve cover removed, noticed sludge. No ticking from top of the engine, only ticking when cold from bottom of the engine. Heads are 862.

Slight loss of coolant. Not sure where. White smoke when truck is cold. 3 months ago had a check engine light for catalytic converter on Bank 2 going out. It was replaced by this first mechanic who did a funky job on welding. I patched the giant gaps myself around catalytic converter with tape I found at AutoZone.

RPM sits mostly at 500. It shakes time to time, as misfire. But no codes at all. When steering is turned it drops to 300 RPM and lights dim then recovers back up to 500. I cleaned throttle body, but made little difference. It did improve very little, but not completely.
Lights dim when fans go off. Even reverse gear dips the RPM. He mentioned nothing.

He and another mechanic say rebuild, or new engine.
I don't know what to do.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

Unfortunately sludge is not a good sign. That shows the truck was not maintained properly and more then likely the engine is on its way out. You may be able to get more life out of it by keeping it maintained but with smoke and using coolant, we need to assume you are pushing a head gasket out.

So let's check that and based on this I suspect the misfire is a loss of compression.

Here are guides that will help with testing both of these:

https://www.2carpros.com/articles/how-to-test-engine-compression

https://www.2carpros.com/articles/head-gasket-blown-test

Let's run through this material and let me know the results and we can go from there.