Knocking Noise

Hey guys I’m trying to figure out where this knocking noise is coming from. I’m seeing a variety of causes on here ranging from it being normal, to vacuum pump, to a connecting rod failure. It is a 2015 SR5 4x4 Automatic. I will post a video. The sound isn’t just the normal tick, it’s deeper. It also doesn’t seem to increase frequency on acceleration. It makes the noise randomly and for random periods. It has fresh oil and filter and gets frequent oil changes. Thanks!

https://vimeo.com/734728247

 

Well I don't know what it is, but it doesn't sound good at all.

Have you tried a sethoscope to find where the sound is actually coming from, such as the lower engine area of the head ...

 

Does it happen to coincide with your A/C being on?

 

I can try that this evening!

I have tried it with the AC off and it still happens

 

Make sure that the Defrost Mode is not on as the AC will turn on in Defrost mode too. Or you could pull the MG CLT
Relay which will make sure that the AC Compressor isn't coming on.

 

That's definitely not normal, I'm just not a good enough internet mechanic to tell you exactly what's going on with it. It does kind of sound like the knock you would get from a rod bearing wearing out and getting sloppy though, but I've only heard that on 4 stroke dirt bikes so I don't know if it sounds the same in a bigger engine.

 

That's the other thing I was thinking, but would that be a higher pitched ticking noise?

 

On a cold motor, pull the serpentine belt off completely. Start the truck up. If the noise is still happening its NOT something that is spun by the serpentine belt.

 

The only thing thats not being pumped would be coolant and hence why i said do it on a cold motor. Oil pump is internal and driven off the crank.

I dont know of a single CONSUMER grade motor that has ANY external belt ran oil pump for this very reason, you loose a front accessory belt of any kind you can continue to drive for at least a little bit to get out of harms way without ruining the motor almost instantly with no oil pressure.

 

This is accurate.

 

I bought a stethoscope and listened in a few different locations. These are where it seems to be loudest. Where else should I listen into?

 

I also just put higher octane gas in. I was running 87, I was at half tank but filled the rest with 93. I have also noticed that it SOMETIMES increases with RPM. But only at low RPM as I start to accelerate.

 

With the engine off reach in and grab the fan, try to wiggle it up and down to check for any play. Also you should be able to see if any of your idlers or belt tensioner pulley is loose or wonky.

 

You can confirm/eliminate internal engine damage (rod, wrist pin, piston slap) disabling one cylinder at a time by removing spark or pulling injector plug if accessible. But get confirmation that pulling spark wire won't damage coil since on some engines it might in which case they use a spark tester in ground mode.

I used this method once to successfully isolate piston slap on a motor.

 

Jezus. STOP.

It takes 30 secs to remove the serpentine belt and start the truck. This will let you know REAL quick if its internal or something transmission/torque converter related.

If there is no noise its something that the belt spins up front thats the problem, simple as that.

Turn the truck off then spin things by hand to find the noisy / worn out component.

 

Okay I will be sure to do that next! Thank you for the suggestions. Sometimes it takes a few minutes for the noise to happen, so with the belt off is there a limit on how long I should run it for heat reasons?

 

In that case. Take the belt off and spin all the components it spins by hand before starting the truck to see if you can find the one with bad bearings. If not start it up and I wouldnt run it for more than a minute or two. Not sure where the temp sensor is within the motor so it may or may not register actual water temp on the dash without the pump moving water through the block.

 

I got the belt taken off this evening. I ran it for a little over a minute and no noise, sometimes it doesn’t always do it right away but still a good sign it may be belt driven. But I did wiggle everything that the belt was on and two idlers seem to have some wiggle to them. I’m not sure if there’s a certain tolerable level so I will attach a video. The compressor also has a bit of a grinding noise when spun and I will attach that video too.


https://vimeo.com/735070482

https://vimeo.com/735070936

 

What works for me. Use a wooden dowel or long skinny screwdriver. You’ll be able to sorta feel the vibration the noise is making. Blip the throttle to make the noise and vibration to change.

You could also put a breaker bar & socket on the crank, rock it back and forth, rotate slightly, do it again, repeat. It’s way easier with the plugs out. You might hear a clunk clunk noise.

 

Take a cup of water and pour it on to the tension pulley. If that's the culprit it might make the noise go away during that time.