'88 6.2 with a new noise

[Lightyear]

My '88 Burb with a Banks turbo-kitted 6.2 and 259K has developed an odd noise...sounds kind of like a 'chugging' sound. I think it's coming from the left-hand cylinder bank. You can hear it inside the truck as well as outside. After the truck sits overnight, it is almost not audible for about 15-30 seconds, then the noise begins. Any suggestions? Lifters? A bad valve? Dogs and cats living together? Thanks.

[DmaxMaverick]

Power steering/brake pump? (usual suspect)

Vacuum pump?

Injector line in contact with something?

Harmonic balancer? (Always check this!)

Good luck!

[Lightyear]

Thanks! What exactly do I look for on the balancer? I think I can figure out the rest of the suspects.

[DmaxMaverick]

The balancer is an outer steel ring and an inner steel hub. They are separated by a rubber insulator, which is the part that fails. If the rubber either gets hard/cracked, or softens and oozes, it's bad. Much like motor/tranny mounts will do when they fail. A bad balancer can be responsible for broken cranks, and other bad things.

If the balancer outer ring is firm and solid, and the rubber isn't hard and cracking, it is good. If you can move the outer ring by hand, it's bad. If you pry against it (don't do this on purpose), it will have some movement. If it seems sloppy, or wiggles, it is bad.

With the miles you have on it, the balancer should be replaced, regardless of the apparent condition.

[Lightyear]

I checked the balancer just a bit ago. It will wiggle a little bit with pressure from both hands; it doesn't wobble on the crank, but there is a little rotational play. I have a service appointment at my local GMC shop tomorrow morning. With 250K plus, what else should I be looking for? I've put 46K on the truck myself since last January, and I plan to keep it for a while. It's stout, comfortable, roomy, good for road trips as well as the commuting madness here in Atlanta, and most of all my dog loves it. Thanks again for the tip.

[DmaxMaverick]

Hmmmmm....

Timing set (gears are premium).
Water pump
Injectors.
Belts/hoses, etc. (no brainer, have them handy)
Motor/tranny mounts.
Toss the EGR, if you have one.
Brake system flush, rear slave and proportioning valve replacement. (commonly neglected)
Power steering system flush. (commonly neglected)
Cooling system flush/cleaning. Rod the core, clean the outer areas of the radiator and A/C condensor.
Body and spring hanger bushings.
Door hinge pins.
Steering column bearings.

Wheel bearings, ball joints, diff's, transfer case service, etc.

The list goes on. It all depends on what has been done previously.

[Lightyear]

New balancer installed on Friday...it idles rock-steady, but the mystery noise is still present. I've also noticed a slight drop in boost; could this be an indicator of a valve train problem? I'm changing oil/filter tonight, will at least visually/hands-on inspect the list you mentioned. The saga continues...thanks for the help!!