Loud High Pitched Whine

[MacDR50]

So I am towing 13k up and down some nasty hills with the grade brake cutting in on the the downers and tranny temps hitting 190F when I have to almost stop at the bottom of a long steep hill because of a bad bridge surface. As I climb the hill I am hitting 2500 - 3000 rpm when suddenly a loud whine starts coming from near the firewall. It was really high pitched and varied with engine speed. Very pronounced at over 2000 rpm. I limped at slow speed to the next available pull-off and let the tranny temp drop to 160. No more whining when I started off again but hills were more gentle.

Any ideas on what caused the noise?

[More Power]

So I am towing 13k up and down some nasty hills with the grade brake cutting in on the the downers and tranny temps hitting 190F when I have to almost stop at the bottom of a long steep hill because of a bad bridge surface. As I climb the hill I am hitting 2500 - 3000 rpm when suddenly a loud whine starts coming from near the firewall. It was really high pitched and varied with engine speed. Very pronounced at over 2000 rpm. I limped at slow speed to the next available pull-off and let the tranny temp drop to 160. No more whining when I started off again but hills were more gentle.

Any ideas on what caused the noise?

The turbocharger resides at the rear of the engine, and will be working pretty hard at 2500-3000 RPM. In addition, the engine driven fan will likely be engaged when the truck is worked hard.

Trans temp is not a problem (from I gotta do something now standpoint) till you're north of 250. In addition, the Allison will protect itself from excessive temps (go into limp mode, set the check engine light, etc.).

Jim

[DmaxMaverick]

Could also be the A/C compressor. They get more noisy as the ambient and underhood temps goes up (increased refrigerant pressure).

[MacDR50]

I forgot to mention the engine wimped out when I heard the noise. It was almost like that run away high pitched whirling sound when an outboard prop clears the water only more mechanical. I though maybe turbo losing suction (cavitation?). Someone suggested the fan clutch slipping. Whatever it was I am sure it wasn't doing any good.

[DmaxMaverick]

The turbo can't really cavitate. The air filter could fail or become completely blocked, though.

With your description, look for an intake plumbing leak between the turbo and plenum (intake manifold). Sounds like one of the large blue hoses may have loosened. When they do, they will blow off boost pressure under load. Less likely, it could be on the exhaust side. Do you have a boost gage installed? If so, you can watch the boost. If it's an intake leak, it will usually dump power/pressure pretty consistently (if a hose leak). Also, check the aluminum intake pipes for chafing. They can abrade through if contacting something.

[More Power]

If the truck is going into limp mode, a diagnostic trouble code will be recorded. So, are there any stored trouble codes?

Having a set of EGT & boost pressure gauges can also help with these sorts of problems. For example, if the sound you're hearing coincided with a drop or fluctuation in boost pressure, it would help with diagnostics.

Like Dmaxmaverick suggested, look at all of the turbo-related hoses & pipes for a possible leak. I do know that some of the LLY trucks had trouble with the turbo/intercooler hoses.

Jim

[MacDR50]

Thanks guys. Will do the checks. How do I know if a code was generated?

[DmaxMaverick]

Thanks guys. Will do the checks. How do I know if a code was generated?

Your SES lamp will be on, you will often be limited on power, RPM range, and sometimes (depending on the code), be stuck in one gear.

[MacDR50]

Thanks. I assume I need a reader to get the code. I'll have it checked at dealer.

[Mark Rinker]

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=34161&highlight=intercooler+hose

[MacDR50]

Thanks Mark. What and where is the intercooler hose in question? I am putting it up on a lift next week to give it a bottom check. Is this something I access from below or from above?

[MacDR50]

Did some research and now know next to nothing rather than nothing. I found what an intercooler is and where its located. Thanks again for the help.

[DmaxMaverick]

My apologies. I, and many others here who have been messing with these things for years, often assume everyone knows what we are talking about when it comes to parts on the trucks. Obviously, this is not always the case. Our failing, not yours. There are no stupid questions....Only questions unasked.

Just so we can make sure we are on the same page:

The "suction" side of the intake is the air cleaner, to the turbo compressor (aluminum half of the turbo, connected to the air cleaner ducting). The pressure side of the intake (often referred to as the boost side/circuit), is everything between the turbo compressor and the intake plenum (manifold). The intercooler plumbing includes the large aluminum pipes, large blue hoses to and from the intercooler, and the intercooler.

If you have loose IC plumbing, it can and often will make the noise you describe (sometimes like a "whoopee cushion"). Many times, a leak can be identified by feeling the hose connections and clamps (you shouldn't be able to move them by hand), and an accumulation of oil/grime residue in the area of the leak. The oil is more prominent on the later trucks, with closed-loop crankcase ventilation (does not vent to atmosphere, like LB7's, but back into the intake on the suction side, before the turbo compressor). Yours is closed-loop. Closed-loop systems can allow pooling of oil (condesned oil vapor from the CC vent) in the intercooler (low point), and the lower plumbing points. It can also cause an internal coating of oil residue throughout the pluming.

[madmatt]

I've replaced a couple of turbos on LBZs for similar issues.

[Mark Rinker]

I've replaced a couple of turbos on LBZs for similar issues.

What fails?

[Mark Rinker]

Thanks Mark. What and where is the intercooler hose in question? I am putting it up on a lift next week to give it a bottom check. Is this something I access from below or from above?

Driver's side, underhood, look straight down in front of battery. Blue hose with clamp connects duct to intercooler. That is where ours came apart.

If these fittings fail, you'll also see black smoke on acceleration. This is unburned fuel, due to lack of air for proper combustion.

[madmatt]

What fails?

They just get play in the bearing and start squealing up off idle. Sounds like a non stop belt squeal. usually no loss of performance though.