Engine lagging sound while at hwy speed

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henrylb68
Posts: 1
Joined: Mon Feb 24, 2014 8:24 pm

Engine lagging sound while at hwy speed

Unread post by henrylb68 » Mon Feb 24, 2014 8:36 pm

I have a 2008 GMC Sierra 1500 crew cab z71. A few months ago, I noticed it was making a strange noise while maintaining a steady throttle while driving down the hwy. I even notice it when in cruise mode. It seems to go away when I speed up or slow down. It almost seems as if the truck shift and is lagging but it happens even at higher speeds. It is a low rubble. Any ideas? I had the transmission fluid changed by the dealer at 47000 and has 60000 now started around 57000. Also, I think it started after I shifted the truck from 2wheel to 4 hi and back. Took to dealer and they say 4x would register problem if it didn't shift back properly.

Appreciate the help

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carriedi
Posts: 2573
Joined: Wed Apr 10, 2013 12:42 pm

Re: Engine lagging sound while at hwy speed

Unread post by carriedi » Tue Feb 25, 2014 5:20 am

I am not sure I can understand what you mean. Does your truck have a tach? Is the tach reading higher than normal at cruise? maybe the torque converter lock up is not locking up. Or are you feeling it's like the engine bogging down?

you should drive your vehicle with a scanner hooked up and see what the data stream shows. watch your fuel trims. you can also switch to watch the trans also.

Converter may be slowing up the exhaust flow.

If you hear a noise, does it sound mechanical? Where does the noise seem to be coming from? engine, trans, front, rear? you may need to go to a shop that a tech can go for a ride with you to hear and feel what you are describing. You might need to find a shop with a "chassis ear" to pinpoint the noise.
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Geo4537
Posts: 2
Joined: Sat Jul 19, 2014 2:36 pm

1997 GMC Jimmy V6 engine knocking as RPM increase.

Unread post by Geo4537 » Sat Jul 19, 2014 2:51 pm

My engine starts to clack at about 1800 RPM and gets louder as the RPM's increase. The oil pressure is great when it's cold or driving but drops way down when idiling. There are no oil leaks or signs of burning oil and the oil level is at the full mark on the dipstick. Can anyone suggest what might be wrong?

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carriedi
Posts: 2573
Joined: Wed Apr 10, 2013 12:42 pm

Re: 1997 GMC Jimmy V6 engine knocking as RPM increase.

Unread post by carriedi » Sat Jul 19, 2014 6:14 pm

rod bearing or crank bearing might be bad. you should have a repair shop take a listen to verify if the engine is knocking or if they think it might be something on the top end. sometimes a cracked flex plate will make a noise that sounds like a knock.
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