Can you see lifter tick / engine knock?

Jacob Diagnostician Utah Posted   Latest  
Case Study
Pico Technology
Driveability
2008 GMC Sierra 1500 SLE 5.3L (M LH6) 4-spd (4L60-E)
Engine Noise
Lifter Noise

I am looking for some input and on diagnosing engine knock / tick. In this case I have an obvious lifter tick after this 5.3L was run low on engine oil (several times). 

Many times with engine noise I am asked by other techs / apprentices if it is upper or lower end noise. I have had a difficult time explaining how you can tell with a clear explanation. 

I decided to try using the pulse sensor on a stethoscope (Thanks Hans Jorgensen) to see if I can visualize the noise.

Here is the waveform I captured with a screen shot. Channel A is Pulse sensor / Stethoscope on the oil pan. Channel B is ignition sync on Cyl #1. 

If I use a filter and use 2x vertical zoom I can see two humps after each 90* rotation. My thought is this indicates upper engine noise (something camshaft / valve related). If I saw only one hump that would indicate lower end (Something crankshaft / rod related).

What do you all think. Are the pulses I am seeing even the noise or something else? Am I missing something and way off? Any ideas to use this test more accurately or is there even a need?

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Andrew Educator
Ohio
Andrew Default
 

I would try a knock sensor or tap into the knock sensors already in the valley of the block. It should have better resolution and is closer to the camshaft and crankshaft. You can take a working knock sensor and hold it to the side of the block or oil pan. A knock sensor is essentially a microphone, the greater the knock the greater the voltage generated. The key is to adjust your scope to a…

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Jacob Diagnostician
Utah
Jacob Default
 

I'll give this a try, Thanks.

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Josh Instructor
North Carolina
Josh Default
   

Coming from a GM dealership the picoscope with NVH kit was a required tool. The NVH sensor can either be set to as an accelerometer for vibrations (what most people use it for), or as a microphone. The microphone setting produces the most clear and obvious sounds - it’s amazing! I would use two microphones all the time to compare noises. In your case one on each bank. You can play the sounds…

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Justin Mobile Technician
Utah
Justin Default
 

I have the NVH kit if you want to try this Jake.

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Thanks
Justin Mobile Technician
Utah
Justin Resolution
 

I think interpretation will be the biggest issue. Is it a noise at TDC? If so then the sync would be valuable. Is it a valve issue? Then it would be very challenging to figure out what valve is in what position when the noise occurred. Im definitely interested in a process that will work. I am deaf in one ear so finding noises has always been a very challenging task. This is the number one…

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Josh Instructor
North Carolina
Josh Default
 

it sounds like you guys are close to each other - just keep in mind the NVH kit is registered to a piece of equipment (I forget off hand if it’s the PC, the pico, or both).

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Jacob Diagnostician
Utah
Jacob Default
 

I would love to give it a try. I have been wanting an NVH kit, just need to put the money aside. It looks like the customer is leaning toward fixing it so I'll likely have the truck for a few days before it's repaired.

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Richard Instructor
Florida
Richard Default
 

I think you're going to need something more sensitive than a pressure pulse sensor on a stethoscope. I’ve tried that method for internal engine noises and the problem is filtering out all the other engine noises from the signal unless it’s a very obvious noise. A knock sensor or piezo sensor might work but again it’s a lot of noise to filter out. Jim Cokonis and I have been playing with a few…

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Stephen Technician
Tennessee
Stephen Default
 

I would try a regular mic, near but not on the engine, as a “sync” to help ID which of the noise pulses, picked up by the on engine probe line up with the ones from the proximity mic. The Chassis Ears brand probes are pizo mics that are very sensitive and low cost. The probes are available in two different styles. Only the connector is different, the probes are the same. The pizo element…

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Scott Manager
California
Scott Default
 

Hi Jacob, I performed a similar experiment last year and wrote up a little note up on it here: Although we didn’t perform any repairs on this vehicle, if we were to disassemble the engine I feel it would be nice to have somewhere specifically to look. I strongly believe that using methods like this will allow us to work more intelligently but that cannot happen unless one is to master the…

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Niall Owner/Technician
United Kingdom
Niall Default
 

Just having a mess about with Scott's file, the injector pulse will be before the inlet valve opens? (not sure exactly when). I have placed the overlay where the exhaust stroke for cylinder #1 lines up with the injection pulse, if that's correct it looks like the main noise pulse occurs just as #6 fires. As I said just thinking out loud.

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Jacob Diagnostician
Utah
Jacob Default
 

Thanks for sharing this Scott. I will give it a try with a microphone if I get some time later. I agree someone has to master the process. Hopefully I can get a few vehicles with similar concerns so I can start to figure it out.

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Richard Instructor
Florida
Richard Default
 

Here is a sample of a waveform I collected using an ultrasonic microphone connected to my scope. The ability to adjust the sensitivity and use a directional probe allow you to pinpoint the location of a noise much more accurately. I was picking up a repeating tapping sound right at the valve cover (green trace), that appears to be loudest at the front of the motor (cylinder #1 of this 2005 Honda…

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Jacob Diagnostician
Utah
Jacob Default
 

Richard, this is awesome! I hadn't thought to use an in cylinder waveform to help pinpoint the microphone signal. Looks like it was easier (still not simple) to analyze the cause. It seems like with an overlay you may be able to find the the cause even if you "guess" the wrong cylinder for your in cylinder testing.

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Richard Instructor
Florida
Richard Default
 

Exactly, an overlay would also give us the companion cylinders valve events and we could narrow down the possible locations. Think about other engine noises too. if it was a rod knock I would expect the noise around TDC and BDC. A timing chain issue like a worn tensioner or broken guide might not be a repeating noise that we can match up to a specific cylinder event. What Jim and I are hoping…

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Jim Curriculum Developer
Maryland
Jim Default
 

First off, no vehicles, personal or rental have been harmed in the name of research. Thanks for sharing this little taste, Rich. This is not new technology. I have shared on here before that I started learning the capabilities of this technology applied to the automotive repair field over 20 years ago. The unit I used back then was used in the NASA program to detect leaks in spacecraft. The…

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