‘88 Sierra engine’s knocking, timings right at 0° no CEL but i have 7 codes on my code reader (images below)

[Schurkey]

There's a million things it "could" be. You already know what my experience was.

If you fix everything else, and still get 50-series codes, you're probably going to have to replace the ECM and see what happens...but...DOWNLOAD THE SERVICE MANUAL SET for your vehicle, and follow the diagnostic procedures for the codes.

 

[Beetlejuice]

There's a million things it "could" be. You already know what my experience was.

If you fix everything else, and still get 50-series codes, you're probably going to have to replace the ECM and see what happens...but...DOWNLOAD THE SERVICE MANUAL SET for your vehicle, and follow the diagnostic procedures for the codes.

Yessir! Will do I’ll try to find a good, GM manual. Bout to do this compression test will update this thread when it’s both said AND done

 

[Schurkey]

I’ll try to find a good, GM manual.

www.gmt400.com/threads/88-98-service-manuals.43575/

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

 

[Beetlejuice]

www.gmt400.com/threads/88-98-service-manuals.43575/

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

HEY MAN. I got my compression test done with, I think it’s pretty low I got an average of 140psi all around the highest being 160psi on cylinder 2 and the lowest being 115psi on cylinder 5.

Are those concerning? I removed all spark plugs when I did it, unhooked the fuel pump relay so i wouldnt be dumping into the engine and removed the ignition coil. Does that process sound right or did I miss somethin, it was on a cold engine I don’t know if that matters or not.

 

[Schurkey]

I got my compression test done with, I think it’s pretty low I got an average of 140psi all around the highest being 160psi on cylinder 2 and the lowest being 115psi on cylinder 5.

140--160 is pretty normal.

115 is concerning. There's a problem with that hole. A leakdown test is in order.

I removed all spark plugs when I did it, unhooked the fuel pump relay so i wouldnt be dumping into the engine

The fuel pump will run without the relay, if the engine develops oil pressure with the ignition "on".

Better to pull the fuel pump fuse.

and removed the ignition coil.

GROUND the coil wire by removing the coil wire from the distributor cap, and securing it to a grounded jumper wire.

Or disconnect the electrical connectors from the coil. Whichever is easier.

Does that process sound right or did I miss somethin, it was on a cold engine I don’t know if that matters or not.

Some folks insist on a pre-warmed engine. I don't think it makes a lot of difference.

You would need to block the throttle at least part-way open, so the cylinders can draw air without restriction.

 

[Hipster]

Is/was there mouse crap/nests anywhere? I once got into a different form of GM product that went goofy like this with the sensor codes when mice got into the 5v sensor circuits. You need to make sure there is nothing shorted to ground. Power through the ground circuit can fry an ecm.

 

[Erik the Awful]

Retest that #5 cylinder. When I compression tested my son's '94, I had a couple cylinders come up low, but the spark plug threads felt a bit crusty. After threading the tester in and out for two or three tests, they all came up.