Engine Knock

Tiny
BRANDON WALTHERS
  • 2006 CHEVROLET TRAILBLAZER
  • 4.2L
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 160,000 MILES

Hey just looking for some extra insight. Here is the problem: two weeks ago I put a scanner on my SUV it said bad cam shaft sensor or bad crank sensor so I put a cam shaft sensor in first because well it was easier to do first. The problems I had went away and ran fine codes went off. After a week codes came back after another week truck is doing the same thing. What it is doing is run rough on low idle feels like it is misfiring has a knocking noise upon start up. When you go to higher idle then smoothed out around after twenty mph sometimes it will shut off when sitting on normal run idle sometimes hard to start. I have a guess which I hope it is not, but my guess is the timing chain?

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Wednesday, October 4th, 2017 AT 8:24 AM

7 Replies

Tiny
2CARPROS KEN
  • ADMIN
  • 11,075 POSTS

First off thanks for the video, that is the sound of a rod knock no need to try to save it, it is time for a new or rebuilt engine.

Sorry about that, I do not like giving good people bad news.

Please let us know what happens.

Cheers, Ken

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Wednesday, October 4th, 2017 AT 4:11 PM
Tiny
WILSONTR427
  • 2005 CHEVROLET TRAILBLAZER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 76,000 MILES

2005 Trailblazer, six cylinder, 4x4, has a knocking noise when it is cold. Noise goes away after warmed up. This started after I had the head replaced from overheating. Does anyone know what this could be?

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Wednesday, October 4th, 2017 AT 8:30 PM (Merged)
Tiny
ERNEST CLARK
  • EXPERT
  • 1,753 POSTS

First a little advice for the future. When an engine overheats and cause enough damage to blow a head gasket or cause you to replace an entire head, that engine should be rebuilt completely or replaced with another. It is sort of like giving a kidney transplant to an alcoholic.

Now for your present situation, I would have to be sure your "knocking" sound is the same as my "knocking" sound.

What I call knocking is a term to describe "pre ignition". This is when there is a severe lean air/fuel ratio in the engine, or a hot spot that is causing the fuel mixture to ignite before the spark plug tells it to. (That is a very simplified version)

This could quite possibly be your problem, but the computer would no doubt see that and set a code. So do you have a check engine light on? If so, have the computer scanned.

Also, a lot of people hear a noise and call it "knocking", but what they're hearing is piston slap or a bad rod/main bearing. (The force of the piston is pushing the crankshaft against a worn bearing during the power stroke)

Everything I mentioned so far can be issues experienced with an engine after a severe overheating situation. With pre ignition, this can be solved by correcting whatever is causing the lean air/fuel mixture. With piston slap, you can try a heavy weight oil, but most likely you will have to live with it unless you want to rebuild the motor. With the rod knock, make sure the oil filter is not clogged, and maybe use heavy weight oil. You will also have to live with it, but your engine will not live for long.

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Wednesday, October 4th, 2017 AT 8:30 PM (Merged)
Tiny
JAX991
  • 1993 CHEVROLET TRAILBLAZER

180,000 miles on engine. My daughter was driving it when it shut off. It had gotten hot and would not start when I first arrived. It later started but has an obvious knock at idle and worsens with rpm. I have not driven it much since, and it seems to idle and run fine. How bad is the damage?

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Wednesday, October 4th, 2017 AT 8:31 PM (Merged)
Tiny
MCFERRANCE
  • MEMBER

Sounds like a rod knock which means machine work or replacement to the crankshaft and rods. Most likely very costly. May be better off with a replacement engine.
Check with a local mechanic who can hear it to get another opinion.

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Wednesday, October 4th, 2017 AT 8:31 PM (Merged)
Tiny
SCMCC10
  • 1997 CHEVROLET TRAILBLAZER

I have a 1997 S10 Blazer with just a little over 100,000 miles. Yesterday it ran fine all gauges were good. Today when started the engine knocks very loud and the oil pressure gauge is through the roof. Wondered if maybe it was the oil sending unit and if so where is that located? Any other advice is greatly appreciated.

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Wednesday, October 4th, 2017 AT 8:31 PM (Merged)
Tiny
SCMCC10
  • MEMBER

Well thank you for your response. Yes oil was the first thing I checked. I figured it out actually and it was a lifter that was stuck. I let the truck idle for about ten minutes to warm up and since then no problems. Must have gotten some dirt or something that caught it just right. Thanks again guys!

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Wednesday, October 4th, 2017 AT 8:31 PM (Merged)

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