Bad motor or ?????

[Dethtats78]

I got a 96 ECSB with a 98 motor with about 140,*** miles on the motor. So a couple weeks ago I got on it a little hard leaving a stop sign and afterwards I noticed a major loss of power and a small knock under normal idling conditions so I limped the truck home (2 miles). I started checking and noticed number 3 and 5 cylinders not firing so I bought a set of wires, plugs, cap and rotor button. Now it is getting fire but the knock has gotten worse and when under a small load such as a little grade, it knocks hard......
I am sure the engine is toast, but I just wanted to check to see if anyone has any ideas before I drop a couple grand into a new motor. I believe it may be a rod knocking from the research I have done and compared it to the symptoms I am experiencing. Any help is greatly appreciated. Thanks in advance!

 

[94Chevyshorty]

It only does this when its under a load? Could be a bad lifter, any engine mods???? I would say check your 02 sensors, i had alot of misfiring and limp mode all day with a bad 02. they usually like to rust so bad theyll fall out of the pipe. But if youve got a knock under a load and it gets worse with more load, ive seen alot of trucks with that same issue have major piston slap inside the cylinders (which by now means the engines sidewalls are toasted)

 

[Ironhead]

Back to basics here. Check for codes. Do a compression check. If all good so far, you need to check fuel delivery and spark, so fuel pressure, and spark problems should show up as a code.

If all is still good, I'd be inclined to check valve operation by removing the valve covers and check the action of each rocker while someone cranks the engine.

No exhaust leaks (can be noisy)

The idea here is to eliminate simple and cheap things before yanking the engine, which is major work and major money.

 

[Dethtats78]

Thanks guys, I will look into the valves and so forth as soon as I can and I will keep you all updated. I do have one question, I have had the valve cover off once before due to a oil leak repair I had to remove the A/C compressor and bracket in order to get it off. So how do I run the engine with the serpentine belt off while checking the valves?

 

[SAATR]

You don't run it for very long. Minutes at a time, as you won't have any coolant circulation.

Sent from my XT1585 using Tapatalk

 

[Ironhead]

If you just want to check valve operation (cam, lifters and rockers), all you need to do is remove the spark plugs, and have someone crank the engine. You might even be able to turn it over using the crank pulley or the belt.