Engine pitch changes at 65 MPH - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


GMC/Chevrolet Truck/SUV When starting new posts, please specify YEAR, MAKE, MODEL, ENGINE type, and whatever modifications you have made.

Reply
 
 
 
Thread Tools Search this Thread
Old 03-13-2014, 11:59 AM   #1
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
Join Date: Jan 2014
Posts: 10
Thanks: 0
Thanked 1 Time in 1 Post
jekokmey is on a distinguished road
Default Engine pitch changes at 65 MPH

This is going to be hard to explain, but lets see.

02 Sierra 186,000 miles 5.3 L - At high speeds the truck seems to perform good but at 65 MPH or greater the pitch in the engine changes as if it bogging down. I don't feel any loss of power but the change in pitch is noticeable by everyone riding "even the wife" asked about it. Sounds like a leak in the exhaust she says. When pressure is put on the motor you hear it at 65 or higher, but when released it goes away until you accelerate again above 65. When the speed drops below 65 and traveling at 55 and accelerate it doesn't happen, only at 65 or greater. This just starting to happen in the last 7,000 miles or so.

Any idea'*?
jekokmey is offline   Reply With Quote
Old 03-13-2014, 07:20 PM   #2
Senior Member
True Car Nut
 
jwfirebird's Avatar
 
Join Date: Dec 2009
Location: western,ny state
Posts: 9,616
Thanked 563 Times in 481 Posts
jwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond repute
Default

does the rpm change with the noise?
jwfirebird is offline   Reply With Quote
Old 03-13-2014, 09:18 PM   #3
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
Join Date: Jan 2014
Posts: 10
Thanks: 0
Thanked 1 Time in 1 Post
jekokmey is on a distinguished road
Default

No, it doesn't appear so.
jekokmey is offline   Reply With Quote
Old 03-14-2014, 12:29 AM   #4
Senior Member
Posts like a Turbo
 
chevy82's Avatar
 
Join Date: Jan 2014
Location: Missouri
Posts: 396
Thanked 99 Times in 84 Posts
chevy82 is a glorious beacon of lightchevy82 is a glorious beacon of lightchevy82 is a glorious beacon of lightchevy82 is a glorious beacon of lightchevy82 is a glorious beacon of lightchevy82 is a glorious beacon of light
Default

Try duplicating the noise by powerbraking the truck to narrow down the noise. With that many miles, motor mounts could be worn, also have seen issues with the transmission dipstick tube hitting the firewall. And seen some tahoes with a bad exhaust pipe moan noise. If its a exhaust leak check for broken manifold bolts at the cylinder head and cracked a exhaust manifold.
chevy82 is offline   Reply With Quote
Old 03-16-2014, 08:29 PM   #5
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
Join Date: Jan 2014
Posts: 10
Thanks: 0
Thanked 1 Time in 1 Post
jekokmey is on a distinguished road
Default

Thanks for the help thus far. I did a check for motor mounts by power braking and checking for engine movement, no movement. Crawled underneath and tried to wiggle and move the exhaust, nothing as everything feels tight. Transmission dip tube feels snug.

Here is some more information that may help. About 3 years ago the cadillac converter was replaced as it coded to be plugged, weeks later I removed the heat shield because it was rattling. At times after start up and until things warm up I will get a rattling thumping sound that appears to be coming from underneath. It sounds like heavy metal on metal then goes away usually in about 5 minutes, but only noticeable when moving less then 20 MPH and goes away when idling and not moving. It could be happening at higher speeds but unsure. I can't reproduce this as it is very intermittent. RPM at 65 mph is about 1900 and MPG is 15.5 the last two fill ups. Above 65 mph the motor will begin to roar at a different pitch, but if gas is released it goes away. Then when gas is applied again above 65 it reappears. Unsure if any vibration is occurring, if it is it is very little to know for sure. Tire wear is about 50%.

Last edited by jekokmey; 03-16-2014 at 08:34 PM. Reason: more info
jekokmey is offline   Reply With Quote
Old 03-17-2014, 06:14 PM   #6
Senior Member
True Car Nut
 
jwfirebird's Avatar
 
Join Date: Dec 2009
Location: western,ny state
Posts: 9,616
Thanked 563 Times in 481 Posts
jwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond repute
Default

ls engines commonly have the exhaust issues he listed, the heat sheild for the manifold, manifold gaskets, etc is where i would look first, look for soot escaping, black marks etc. the heat shield on many of them ends up rusted through, you dont really need it
jwfirebird is offline   Reply With Quote
Old 03-18-2014, 05:54 PM   #7
Senior Member
Posts like a Turbo
 
chevy82's Avatar
 
Join Date: Jan 2014
Location: Missouri
Posts: 396
Thanked 99 Times in 84 Posts
chevy82 is a glorious beacon of lightchevy82 is a glorious beacon of lightchevy82 is a glorious beacon of lightchevy82 is a glorious beacon of lightchevy82 is a glorious beacon of lightchevy82 is a glorious beacon of light
Default

I know you replace the cat a while back, are you sure its still intact on the inside? Have seen some shop throw cheapies on and make noises later in time. Just a thought.
chevy82 is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
HIgh Pitch Squeal. Is this normal? BrightonBonneGXP Bonneville GXP/ Northstar Powered Cars 11 08-23-2006 10:46 PM
High pitch sounds from subs... driverjohn2005 Audio (and aftermarket electronics) 7 02-21-2005 08:16 PM
High pitch squeal while driving... Hans 1992-1999 8 02-17-2005 04:18 AM
CAN YOU LEGALLY TINT CAR WINDOWS PITCH BLACK TORQUE General GM Chat 42 01-01-2005 06:43 PM
How to change headlight pitch on my 98? Allmachtige 1992-1999 3 06-23-2004 12:42 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 02:28 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.