Just replaced the intake manifold on my 2002 5.3L suburban. Started it up fine, idled beautifully for several minutes, then suddenly died. Restarted and had an awful knock. Turned it off right away. Restarted it to pull back into the garage, gets worse under load.

Sounds like a rod knock? Seems strange that replacing the intake manifold would induce this, unless something got sucked in the cylinder?
Any ideas? Help...

 

I had that same thing happen after I put a used engine in my 01. Swapped intake manifolds from my old engine to the one I put in. Fired it up, idled fine for 5 min or so and then it started knocking like a rod was ready to come out. I checked for sticky valves and other small top end things. Plugs looked fine. I finally got frustrated enough I went and drove it. Once it got hot it went away and never came back. I put 10k on it then sold it about a year ago and it's still running. I'm curious to know what was actually causing it.

 

Started digging into the engine, found what uesed to be a nut and washer in cylider #3. Dissapointing, thought I was careful to not get anything in the intake ports, vaccumed out and all. Must have gotten in as I wrangled the manifold back into place. Can't figure out where it came from though, not missing anything upon re-assembly. Fortunately no significant damage done other than to my pride and time spent. Also found that the rear exhaust manifold bolt wasn't there upon pulling the head. It was sheered off flush in the head. Must be a factory option, no work has been done on the car since we drove it off the lot new (other than routine maint.). Now I need to get that drilled out.