Engine Knock 1994 6.5 TD Suburban

[69ra3ta]

I have a 1994 6.5 TD Suburban which I ordered new in 1993. Last year it developed a knock. Oil pressure is fine. I checked the oil for shrapnel and have found nothing. I removed the serpentine belt to rule out any belt driven accessories. Knock still there. Still concerned, I dropped it off at the dealer (twice). They are still scratching their heads. I ended up just driving it around locally only. Then I noticed when it warmed-up, the knock subsided. Exhaust leak, no. So feeling a bit more confident, the drives got longer and the truck has seen an additional 15K miles since the knock started. I keep an eye on the oil for evidence, nothing. The Sub has 200K on it now and still runs smooth and strong. Here is some history. 4 Injection Pumps, relocated Controller, Banks kit, upgraded cooling system with dual Thermostats, recent Turbo and Injectors, very well serviced. Any ideas?? Thanks, Doug

[rustyk]

I had a (maybe similiar) issue in my 6.5L TD motorhome - the damper/pulley was totally shot, and was striking the stops.

[69ra3ta]

rustyk, Thanks for the tip. I will inspect it for damage. Do I have to remove it to inspect for damage or will it be obvious while still on the motor? Doug

[Cowracer]

It is not uncommon for the aluminium coolant pipe going from the thermostat housing to the heater core to wind up in contact with an injector line.

The injector line gives the pipe a good thump every time the injector fires, which makes the heater core knock.

This sounds EXACTLY like a rod knock inside of the cab, and will make you think the engine is coming apart. Let it idle and put you head in the passenger footwell. If the knock sound like its coming out of the HVAC housing under the dash, that may very well be the problem.

Tim

[Shikaroka]

A bad injector will make a noticable knock.
The warming up part makes me suspect a bad or week injector.
Most guys recommend replacing them every 100k miles or so, whether you think they need it or not.
My Burb got alot quieter after I replaced the injectors.

[69ra3ta]

It is not uncommon for the aluminium coolant pipe going from the thermostat housing to the heater core to wind up in contact with an injector line. Tim


Cowracer, Thanks for the reply. I have replaced the coolant line you speak of. The knock was there before and is still there. The coolant line is not in contact with anything. But thanks. Doug



A bad injector will make a noticable knock.
The warming up part makes me suspect a bad or week injector.
Most guys recommend replacing them every 100k miles or so, whether you think they need it or not.
My Burb got alot quieter after I replaced the injectors.


Shikaroka, Thanks for the reply. I suspected the injectors in the begining and replaced them. Still have the knock. Thanks, Doug