1999 GMC Sierra knocking sound in engine

Tiny
METZA1
  • MEMBER
  • 1999 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 135,000 MILES
Most of the time (probably about 80% of the time) when I accelerate from a dead stop, I get a rapid knocking sound from under the hood. It also makes the noise continuously if I’m parked facing up a steep hill. If I rev the engin while not in gear, the is no noise.
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Wednesday, May 20th, 2009 AT 9:06 PM

6 Replies

Tiny
OBXAUTOMEDIC
  • EXPERT
Hello,

When did this start?

A couple possibilities.

Spark Knock - Try Higher Octane Fuel

Timing needs attention - Check timing,

Also when was last tune up Cap, Rotor, Plugs and Wires.

And if haven't had timing chain changed it is probably time.

Another possibility is a weak Oil Pump, check oil pressure.

.
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Wednesday, May 20th, 2009 AT 9:26 PM
Tiny
DR LOOT
  • EXPERT
It does not sound like the engine to me, it sounds like you have drivetrain problems, first of all get underneath your truck and check all of your U-joints to start with.
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Wednesday, May 20th, 2009 AT 10:23 PM
Tiny
OBXAUTOMEDIC
  • EXPERT
I would almost agree Dr Loot if it wasn't stated that "It also makes the noise continuously if I'm parked facing up a steep hill." How would it be making the knocking if standing still.

However, more detailed info on the problem would help out a lot.

.
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Thursday, May 21st, 2009 AT 10:53 AM
Tiny
DR LOOT
  • EXPERT
I believe your truck has an anti-knock sensor on the right side of the block by the starter, it is round about 2 1/2 inches in diameter, with one wire going to it, it's supposed to work under load only, so get on Mitchell 1 and find out how to diagnose it.I got on Mitchell 1 but I cannot find anything on the anti-knock sensor can you check and see if you have one on your truck? And get back to me.
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Thursday, May 21st, 2009 AT 12:51 PM
Tiny
OBXAUTOMEDIC
  • EXPERT
The Knock Sensors are located in valley under Intake Manifold... This is the location for both 1500 & 2500 series and all V8's....


http://www.2carpros.com/forum/automotive_pictures/188069_99gmcsierra1500knocksensors_2.jpg



Here is Test Proceedure....


http://www.2carpros.com/forum/automotive_pictures/188069_99gmcsierra1500knocksensorstest_2.jpg



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Thursday, May 21st, 2009 AT 2:33 PM
Tiny
DR LOOT
  • EXPERT
O.K. You don't have to kick my A$$ I'm just trying to help. It must not be a knocking sound it has to be a backfire? The only other thing it can be is the cam or a bad lifter or a valve, sorry Loot Bug, it's like the blind leading the blind, if I could hear the noise, maybe I could come up with something, if I can help let me know.
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Thursday, May 21st, 2009 AT 10:51 PM

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