Compression tests - Conventional vs. Labscope

Brian from Willoughby Diagnostician Posted   Latest  
Demonstration
Education
Relative Compression

Brandon Steckler compares two tests in this recording.

One being the conventional method of compression testing vs. a more modern version called relative compression testing. When beginning your diagnostic approach on any diagnostic routine, it is always best to develop a route to travel early in the game.

One early step in that approach when diagnosing a misfire should include a relative compression test. This test is non-invasive, very quick and powerful​.​We want to know early on if we suspect there may be a mechanical failure or not before performing more invasive tests.

Thanks for watching!

youtube​.​com/watch?v=AsJQls…

+9

Steve from Northwich

 

Owner/Technician
 

Some very big names in that video, a great example of non intrusive testing.

Here's an engine with a fault using the same test.

youtu​.​be/_e-fJHEyPxA

+2

Brandon from Reading

 

Diagnostician
 

I LOVE this guy!😊

+1

Brandon from Reading

 

Diagnostician
 

I really hope to meet you, Steve...”CHEERS”!

+1

Steve from Northwich

 

Owner/Technician
 

If you're ever in the UK we must meet up 👍 I'm hoping to come ride along with Keith DeFazio in the spring. Working with him on completely unfamiliar vehicles will be a true test of my fundamentals 😮

+1

Scott from Claremont

 

Owner/Technician
 

That ride along sounds interesting, might need to bring a camera or two to document this adventure! Do you have a date set?

+1

Steve from Northwich

 

Owner/Technician
 

It looks like end of march, hopefully to coincide with TST. I can't think of a better way to stress test my knowledge, I'm used to being under pressure but imagine working under Keith on completely alien craft. Awesome.

+1

Brandon from Reading

 

Diagnostician
 

Count me “IN” STEVE! I’ll be there, if you’re serious....camera in hand!!😬

+1

Steve from Northwich

 

Owner/Technician
 

I've committed to it, the hype train is rolling 🚂🚂🚂

+1

Brandon from Reading

 

Diagnostician
 

I assure you, you WILL learn from Keith DeFazio, a true craftsman!

+1

Josh from Lynchburg

 

Technician
 

Very well explain process. Thanks for taking the time to make and share the video.

+2

Brandon from Reading

 

Diagnostician
 

Thank you, Josh

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Jim from Southampton

 

Mobile Technician
 

What a GREAT way to start off the New Year with. Brandon’s video can be a real time saver when trying to find the area of the driveability problem. As I’ve said in many of my presentations, most driveabilty problems will fall into one of three Funnels: Fuel Delivery, Ignition related or Engine Integrity. Finding the correct funnel is done by what I call General Test (G’s), then when you have found the correct Funnel, drive down that Funnel with Pinpoint test (P’s). The reason I use the Funnels is because a Funnel is very wide up top and progressively becomes smaller, so let’s say that Brandon found a lower amount of compression in one of the cylinders, we all now that could be caused by many different reasons. So that means finding that lower compression was a “G” test and now performing more diagnostic procedures like a cylinder leakage or using a pressure transducer in that cylinder would be “P” test driving down the Funnel.

There are a couple of notes that I made while watching the video, Now anyone that knows me and my relationship with Brandon knows I Love him like a son, we have spent MANY hours hashing thoughts and procedures back and forth. So I’m in NO WAY criticizing what Brandon said in his video.

The first thing I wanted to point out is how important it is to connect a battery charger up BEFORE you begin testing because as Brandon noted, you want the same amount of energy during all of the cylinders cranking compression. But if at all possible use a Constant Voltage battery charger not a Constant Current battery charger. Most battery chargers in the shops are Constant Current. When you connect it and select 20 amps, that means you will Constantly have 20 amps charging, the possible problem with this is you might actually have the engine spinning faster then normal which could in fact give you a slightly higher compression reading and throwing your readings off. Battery chargers like the Snap-On D-Tec are Constant Voltage battery chargers, they will bring the battery voltage up to a normal level and maintain that level throughout the entire test.

The 2nd thing I wanted to point out is how important the “1st Puff” is on a cranking compression test, I’ve seen too many times where the end readings were all close to each other but the 1st puff was lower on a cylinder or cylinders which indicates cylinder wall or piston ring issues. A General rule of Thumb is you want to see approximately 50% of the final reading on the 1st puff.

As you can see on this waveform, The 1st puff is 82.64 psi and the last one is 162.5 psi.

I will also agree with Albin Moore’s statement, Cranking compression is more of a “Static” way of checking the condition of the engine, always try to do more of a “Dynamic” way of checking.

+3

Jim from Southampton

 

Mobile Technician
 

BTW - I ALWAYS wanted to meet those 2 techs in the ASE questions, you know Tech A and Tech B, that all they ever do is stand around and DISCUSS things??? I think I saw them in that video in the background Discussing some of the questions on the ASE exams.....LMAO

+1

Brandon from Reading

 

Diagnostician
 

EXCLLENT POINTS, Jim! Thanks for including that. I would love to have included those points in the video as well. Would certainly enhance the demonstration!👍

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Jim from Southampton

 

Mobile Technician
 

You Did an AWESOME job on that Video, and even introduced us all to Tech A and Tech B in the background.

+2

Brandon from Reading

 

Diagnostician
 

😆thank you

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Jeffry from Québec

 

Educator
 

Hi Brandon,

The mirror of your face in the screen of the scope near the end is brill. Nice touch.

J

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Brandon from Reading

 

Diagnostician
 

Thanks Jeff,

courtesy of my good-buddy, Chris Martino...he has some cool camera skills

+1

Keith from Collinsville

 

Diagnostician
 

Another tip I like to employ that is equally as valuable as AC coupling, is to invert the scope leads on the battery, this will allow it to appear like a conventional RC test with an amp clamp. Great video Brandon! Glad to have you on the TBT team!

+2

Brandon from Reading

 

Diagnostician
 

Keith,

Thank you, You bring about another great technique!

+1

Cliff from Santa Maria

 

Diagnostician
 

Great explanation for those who aren't doing this testing method.

I know Brandon isn't very tall and he is a bit younger than me, but watching him use such short extensions just sent pain down my back...I like to not lean over when doing plugs if I can get away with it. Keep up the great work my friend.

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Brandon from Reading

 

Diagnostician
 

😆thanks Cliff

0