Relative Compression Testing - Automotive Education

In this video, we talk about Relative Compression Testing. This can be a very useful diagnostic step which can save you a lot of time and money when working on a vehicle. We outline the tools needed and the process followed to perform this test, as well as talk about what information you can get from the scope capture afterwards.

Thank you for watching, I hope you enjoy the video. Please 'like" and Subscribe for more content.

[DIYAutoHomeschool]

Thank You for watching the video, feel free to leave a comment with any thoughts or questions.

[eyesalooking]

The clearest explanation I have seen on relative compression using an amp clamp and scope. Thank you. You explained it in enough detail that I am adding this to my scope knowledge base.

[EshbanAutoGarage]

Very informative.
I'm a mechanic in Nairobi Kenya and I'm thankful for this information.

[Graham_Wideman]

I greatly appreciate Youtubers such as you who put in so much effort. I would like to contribute a revision to your explanation of the initial current spike. That initial peak is not attributable to counter EMF. Its due to the starter motor being initially stationary ("stalled"), which makes it act like almost a short circuit across the battery (well, very small resistance and inductance of the windings). It jumps up to the amount of current that would flow if you just applied the battery to the armature winding, sitting alone and stationary outside the starter motor. But as the motor starts to turn, _then_ it produces reverse EMF (because it's simultanously working as a generator), partially opposing (essentially subtracted from) the battery voltage, and reducing the current. As the motor speeds up, so the "generator effect" increases in opposition to the battery voltage, so the current decreases to the ongoing plateau level you have sketched.

[sheerwillsurvival]

Excellent diagnosis.timing chain I was thinking head gasket at first but then realized they were all about the same value. Genius 👊🏻👍🏻

[istvanmeissler]

I watch a lot of automotive videos on YouTube and learn a lot from all of them, but this was by far one of the best. You kept it to one subject and explained it very clearly and very well. I thank you.

[pctuterman]

Relative compression test explained the way it should be explained. Thanks for such a great video. Now I know for sure why I subscribed to your channel.

[crush]

Seeing how this is hooked up and several clear examples that resulted from this test makes this the most informative video I have seen on this topic...thank you for posting this...

[nickayivor]

What do you call INTELLECTUAL AND PRODIGY AND PROFICIENT AND SUBSTANTIAL ADD ONE MORE KNOWLEDGEABLE THE ANSWER IS
DIY AUTO HOMESCHOOL
My teacher
Thanks for sharing it, start to finish loved it . take care and have a great Evening with all your family around you
ACCOMPLISHED DIY AUTO HOMESCHOOL
From Nick Ayivor from London England UK 🇬🇧

[RobHaag]

I first thought head gasket on the Cadillac, but I'm sure I wound perform a leak down test, but then I might be thinking valves after that. That one could get you into trouble if you didn't know about the timing chain, or be puzzling if the valves seat for you during a leak down. It's nice to have the web to turn to these days for sure. Thanks for the video!

[REPOOCNITSUJ]

Brilliant video!! You have a new subscriber. Please, please, please post more videos like this. I just bought my first scope and I'm fumbling around trying to learn how to use it. This video was very clear and instructive to a new scope user like me. Thanks a million!

[jerradguillory]

👏 subscribed! Alot of mechanic vids i watch they only just walkthrough what they do without explaining what they doing they going through their diagnostic motion with camera on

[hustlerforgita]

You answered some of my question I had with this test thank you very simple explanation thumbs up

[glowvid]

Thank you, you explained it really well

[TheDerekeder]

Wow! Excellent video - thank you so much!

[kenricrose]

Great video! Was looking for some automotive diagnostics I could do with my new scope and this video was a big help. It makes perfect sense but I had never thought of doing this.

[PhillipBailey]

Good video. Just curious about your scope settings when using the low amp clamp, are you using ac coupling? Since starter current would be well over 60 amps I use a high amp clamp with 1mv equals 1 amp.

[samadam]

I love you draw pic on board explains it is best . I watched many videos they good too but they don't explain it on board hope they learn from you . We watch because we want to learn and skip tech school.you best and wish you best I never commented on YouTube but I liked pic on board and made to find away to comment..

[philh]

nice work, like the vids. hope to see more from you!

[rubenvor]

Outstanding and simple explanation! Good job. Thanks a lot/