LB7 help diagnosing.

six5creed

six5creed

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Jan 6, 2016
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Forgive me if this had been covered already. I bought a 2003 GMC 6 months ago and it has 149,000 miles on it. Couple weeks ago I was coming home from work and about 50 mph and 1700 rpm started hearing a funny noise coming from what sounds like top of engine. Sounds like a 3/8" air wrench with low air pressure. It's not constant. It comes and goes. When you mash the pedal it goes away. Then when I started to stop at a light the tranny started downshifting really wierd. It was kinda jerky. The next day it didn't do it. After a couple weeks it all started again today. I have set the edge back to stock and still get it. What could this be? Thanks for any help.
 
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Awenta

Awenta

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Sep 28, 2014
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Have a video? Maybe a boost leak? You might not be able to hear it at wot, doesn't mean it's not there.

The bouncing idle is a sticky fpr. Run some additive.

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chevyburnout1

chevyburnout1

Fixing it till it breaks
Aug 25, 2008
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I wonder if you have a California version LB7 with a vacuum pump. They like to make a noise like that when they start to fail. Are there a bunch of vacuum lines on your fuel filter housing?
 
six5creed

six5creed

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chevyburnout1 said:
I wonder if you have a California version LB7 with a vacuum pump. They like to make a noise like that when they start to fail. Are there a bunch of vacuum lines on your fuel filter housing?
Click to expand...

It is not a Cali truck. It was originally sold out of Virginia. Thanks!
 
TheBac

TheBac

Why do I keep doing this?
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Apr 19, 2008
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Sounds like a bad FPR to me. Bouncing idle, choppy shifts, wants to surge ahead when stopped at a light? When they really have an issue, they buzz.

You really need to have someone put a scanner on it and check rail pressure (among other things) when it happens. It isnt one a person can diagnose from a distance.
 
six5creed

six5creed

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chevyburnout1 said:
If I remember correctly California emissions trucks could be sold in any state. Either way, maybe post a video of the noise it's making?
Click to expand...

I put some diesel kleen in the gray jug and some 2 stroke oil in the fuel, it is getting better and only does it every now and then.
I unhooked the Edge and that didn't change anything either.
It doesn't have any of the Cali emission stuff on it, thanks!
 
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