jenrainbow

Hello,

We purchased a 2000 Yukon Denali and it has a strange 'mooing' sound that occurs --- it does not happen consistently and usually it happens while accelerating, although, it has happened at other times.

Has anyone ever experienced this sound?

Any insights would be much appreciated...thanks!

rzkz8k

Welcome.

I've got this issue on my 04YXL, you will be interested in Bulletin 1550195 whic states:

Exhaust Vibration Resonance or Moan: 99-05 Full Size Trucks and Utility Vehicles with GEN III V-8 Engines - kw 4.8 5.3 6.0 AC acceleration exhaust fluctuation idle intermittent L59 LM7 LR4 LQ4 LQ9 #PIP3121B - (Sep 16, 2004)
Exhaust Vibration Resonance or Moan 99 - 05 Full Size Trucks and Utility Vehicles with GEN III V-8 Engines
.

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Condition/Concern:
Some 99 - 05 C/K sport utility vehicles and trucks with GEN III V-8 Engines and a single pipe exhaust system may exhibit an exhaust vibration that is engine load sensitive. Typically this will happen just off of idle to 2000 rpm on light acceleration.

Recommendation/Instructions:
IMPORTANT: The following does not apply to 2002 - 2004 Full Size C-K Utility Vehicles with an IDLE ONLY vibration. Reference Internal TAC PI AIT3025 for IDLE ONLY vibrations on 2002 - 2004 Full Size C-K Utility Vehicles. .

IMPORTANT: The following does not apply to dual pipe exhaust systems like the ones used on some 3/4 Ton and 1 Ton trucks or like the ones used on the SS Chevrolet Silverado or the GMC Denali Pick Up Truck.

Determine if this is an exhaust vibration by using an EVA tool to gather Hertz readings from various locations (seat track, frame, radiator support, etc.) during the condition.
Multiply the Hertz readings by 60 and the divide the sum of that by the exact rpm that the readings were taken at. The sum of this will determine what order vibration it is. If this is exhaust related, a fourth order vibration will be calculated. Here is an example of a 4th order vibration at 900 RPM:
.

58 hz multiplied by 60 = 3480

3480 divided by 900 rpm = 3.87

3.87 Rounded Up = 4

4 = 4th Order Engine Vibration

.

If this is a 4th order vibration, fabricate 2 dampers using the following procedure:

Obtain 4 dampeners, Part Number 10199232.
Line up 2 dampeners so the dampener pipes are opposite of each other.
Line up one mounting hole from each dampener with the holes of an appropriate size exhaust clamp.
With all of the holes lined up, weld the flat portion of the dampeners together and to the flat part of the exhaust clamp.
Attach the dampeners to the exhaust system using exhaust clamps and the following locations: On trucks with an 8 ft. bed, install one modified damper in front of the muffler and one just behind the muffler. On trucks with a six foot bed, install one modified damper in front of the muffler and one over the top of the rear axle. On Utility Vehicles, place one in front of the muffler and one anywhere between the muffler and rear axle bend. Fine tuning will most likely be necessary, especially on Utility Vehicles.
Note: The locations above are just starting points. If the vibration is not improved, move the dampeners around while using an EVA tool to fine tune the exhaust system by noting the G readings on the exhaust system. There are pictures of these fabricated dampeners on the technician forum at the following link:

http://service-gm-forum.com/techforu...85&h1=dampener

.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

Models:
(01 02 03 04 05 Cadillac Escalade with a GEN III Engine and a single pipe exhaust system) and (02 03 04 05 Chevrolet Avalanche with a GEN III Engine and a single pipe exhaust system) and (99 00 01 02 03 04 05 Chevrolet Silverado Truck with a GEN III Engine and a single pipe exhaust system) and (00 01 02 03 04 05 Chevrolet Tahoe with a GEN III Engine and a single pipe exhaust system) and (00 01 02 03 04 05 Chevrolet Suburban with a GEN III Engine and a single pipe exhaust system) and (99 00 01 02 03 04 05 GMC Sierra Truck with a GEN III Engine and a single pipe exhaust system) and (00 01 02 03 04 05 GMC Yukon with a GEN III Engine and a single pipe exhaust system) and (00 01 02 03 04 05 GMC Yukon XL with a GEN III Engine and a single pipe exhaust system) and (03 04 05 Hummer H2 N2).

My dealer has done this, replaced the exhaust, reseated the engine and transmission, doe this bullentin again and still no relief. The droaning overwhelms the radio during light accelation. Good luck.

ednieda

Hello,
Have you solved your engine moan? I have a 04 Yukon Denali that is pretty loud at around 80Mph. The car is still under warranty and I am heading to the dealer tomorrow.
Regards,
Ed

ednieda

Sorry - dumb comment. I just bought the car used and after bringing it to the dealership, they told me the car has an aftermarket Magna Flow exhaust. Hence the car was modified to have a rumbling racing sound.

tonytone

That's not necessarily a bad thing, especially given the exhaust bong noise issue w/ the factory muffler. Magnaflow mufflers are really nice as far as aftermarket mufflers are concerned; if the slightly-louder exhaust note doesn't bother you, you're definitely ahead of the rest of us stock muffler folks.