2005 Yukon XL knocking.

iam4uf · September 29, 2014

Hi, I have a 2005 Yukon XL 5.3. It has 155,000 miles on it and I bought it brand new. Recently it has been making a knocking noise. It sounds like it is coming from the drivers side front of the engine (see attached video). When I rev the engine the knocking noise goes away. It happens intermittently and mostly at idle. There is no engine light on and runs great.

Anyone have any idea what it could be or is it anything I should be concerned with?

Thanks in advance

Yukon 001-1-1 (mp3cut.net).mp3

Doug_Scott · September 29, 2014

Sounds like a valve train issue. Bad lifter likely since it does not do it all the time. If it was something mechanical like rocker or bent push rod, or even missing lobe from camshaft, there would be other indicators, and the noise would not stop. This sounds like a bad lifter that is not holding pressure internally all the time.

02suburbanZ71 · September 30, 2014

^^ not a cheap fix. Might want to pull an LQ4, LQ9, L33 from the junk yard.

Doug_Scott · September 30, 2014

Forgot to add that at 155k, you are pretty much beyond the idea of just changing a lifter. What does your oil pressure look like at idle? Actually, never mind, get it checked using a real gauge instead of the gauge in dash, if you have one.

To change a lifter, you need to pull intake manifold and rocker covers. Once at that point, it is just a matter or removing rocker arms, push rods and then whatever they use on roller lifters to secure them in the block. You would not just change one at this point, and you also need to verify the cam is still good, no scoring or nicks, marks, etc. If oil pressure what good before doing this, then you may get away with just lifters, but, if pressure was low before, it will still be low, and noise will likely return in short order.

Keep in mind that using a wrecker engine is also a risk. They may warrantee the engine, but they will not warrantee the labour to re and re it. How much longer were you planning on keeping the truck?

iam4uf · September 30, 2014

Thanks for the reply's. I would like to keep this vehicle a long time. Up to now, I haven't had any problems with it. I have been reading on some forums regarding piston slap. People are saying it is normal and not to worry about it.

If it was a problem with a lifter would it make the engine light come on?

Also, would it effect the way it ran?

gmtech4 · September 30, 2014

Runs great == drive truck imo

iam4uf · September 30, 2014

OK, so after doing some research I think I know what the problem is. After viewing some YouTube videos regarding knocking when cold it seems like there is a common problem with GMC regarding exhaust manifold leak. I looked at my SUV and sure enough I have a broken bolt on the drivers side toward the front of the engine. Exactly where I hear the knocking noise. Seems like it is a big pain to get the bolt out and replace.

You guys ever seen this issue? Thanks again for all the replys.

Picture from the top of the engine on the drivers side.

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Picture with mirror where you can see the broken bolt.

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iam4uf · September 30, 2014

Wow, what do you guys think of this? Sounds easy and might be exactly what I need.

Doug_Scott · September 30, 2014

The way you described the noise, and how it behaved, does not sound like an exhaust leak to me. Usually an exhaust leak will not go away simply by revving the engine. It will however increase in speed. Piston slap is usually only audible during cold start, and will stop within seconds of start up.

Exhaust leak will sometimes go away as engine gets hotter. Sometimes it will get worse as it gets hotter. It is worth looking into, have you researched that plate idea in the video at all? From the video it is clearly a patch, not a fix. You have to be careful in making sure the manifold is not starting to crack due to broken stud creating uneven pressure across manifold length. If manifold is already cracked, the patch will not stop the leak. It may actually cause the manifold to break completely at the crack.

A bad lifter may cause a CEL, it can cause the PCM to reduce timing by tricking the PCM into thinking the engine is pinging. If the lifter is so damaged that it stops that valve from opening enough, or remaining open long enough to get enough of a charge into the cylinder that it causes a misfire, the CEL with appear.