Suburban 5.7L Knock



I have a 97 GMC Suburban K2500 5.7L with 82,000 miles that has a deep knock from the bottom of the engine. Two mechanics spent 30 seconds listening to the engine and proclaimed bad piston rods. Can a mechanic diagnose the problem that quickly? Could it be a faulty timing issue? If a sensor malfunctioned could the timing be off enough to cause the knock?

Two months (1500 miles) ago the engine ran fine. 7 weeks ago the engine would bog down and knock when you accelerated above 2500 rpm. The problem has progressively gotten worse. Now after 10 min. of driving, you can?t get above 1200 rpm without the engine dieing. It is hard to start after the 10 min. of driving but will start if you let it sit for 5 min. The engine seem to idle smoothly until 1200 rpm.

The cap and rotor were just replaced. The only computer error codes are P0174, P0171, P0131. The fuel pump was replaced 3 years ago, and you can hear it hum even when it won?t start.


10 years old with only 82,000 miles? Has this vehicle had a lot of hard use and/or mostly stop and go driving?

I’m betting it’s bearing knock. That’s when the engine is worn to the point that the spaces are too big between the crank and bearing surfaces to maintain a pressurized fluid seperation and things start banging against one another. Not good. Can even spin a bearing.


Yes, it was used as a field truck for a land surveyor; so a lot of short trips.
Since it never was equipped with AC, has a large hole in the seat, and possible fuel pump/injectors/pressure regulator problem, a bad engine would put it last nail in its coffin. Anyone have suggestions on what to do with the remains.