Relative Compression with Battery Voltage Check
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- Опубликовано: 14 июл 2020
- In this video, we look at performing a relative compression check by measuring voltage. We will be using the PicoScope 2204A oscilloscope. I will give a brief PicoScope automotive tutorial covering various oscilloscope settings. These settings will help you get the best out of the PicoScope 2204A oscilloscope; other settings could be used with the more powerful 4425 PicoScope Automotive oscilloscope.
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Relative compression is a great quick check, especially on diesel engined vehicles. Very good for the inexperienced technician that hasn’t quite got the ear. I do love a cylinder leakage test. Great video.
J Lang Yeah for sure, a quick check to help make the decision to do a mechanical check (can be labor intensive, especially diesels!). I think I prefer using the amp clamp method. Thanks for watching! 👍
DO NOT reverse the leads @ battery to invert the signal as some are suggesting here!
This PICO 2204a does not have floating grounds. The BNC grounds are connected to each other and to the USB ground.
Create a custom probe with a -1 multiplier to invert the waveform to have it display peaks up like the amp clamp method.
Great info! Thanks 👍
I have a modis ultra....i set my scope to 2 volts ac coupled....peak detect...
2 seconds screen time...and invert the screen.....I have not used an
amp clamp for a relative compression test in years....super fast test....thank you for taking the time to create content for your channel.....very good stuff!!!!!
sonsautomotive Nice one! Sounds like you have your scope diagnostics dialled 👍. Thanks for the feedback, got lots more content to come!
Thank you for your videos. Good job. Have a blessed and safe week to you and your family.
Billy Yoder Thanks!
Great explanation and thanks for showing the scope setup! I used this test on a 1.7 diesel with a 4225 pico. worked well. I could see the difference
It’s a cool quick test!
Very good information thanks
Great stuff. Nice & clear explanation. Keep it coming!
Thanks for watching!
very educative. Thank you regards
Very nice explanation of changine the sampling to minimize noise. That said, I have an amp clamp, so will use that instead of voltage. Thanks for the video.
Thanks! Yes I’m not sure people will adjust sample rate very often. I suppose if you have the 4425 or similar, you can just use the filter while maintaining the high sample rate. But I agree, amp clamp is better. Thanks for watching!
Great job, very professional
Glad you enjoyed the video, thanks! 👍
Awesome video lots of great information. I like to keep it simple and use an amp clamp. My brain gets a little foggy after lunch so keeping it simple helps . Keep the videos coming.
Always keep it simple! I think the amp clamp is probably the better option. I will probably do a proper side by side comparison at some point. I was actually surprised that the amp clamp picked that fault with the loose plug! Can’t work out why the voltage check didn’t. Thanks for watching!
Would that be a liquid lunch :)
Excellent
Olá, sou do Brasil e seus vídeos são ótimo. Comprei este osciloscópio para começar e estou muito feliz com os seus conteúdos.
Ótimo ouvir isso! Obrigado por assistir 👍
For the most part, if I have enough grounds to believe a misfire is being caused by the engine itself, I want a complete compression and leakage test on all cylinders to determine the overall health of the engine, no exceptions. Anything short of that is leaving yourself open. I acknowledge that the relative compression test exists, and that maybe it can in some cases accurately pinpoint a weak cylinder by monitoring cranking current (or in this case voltage)… But still, there’s no way I’m ever taking those findings to the bank, nor even wasting time with this test in the first place because it’s too easy to get burnt. Besides, numbers give a much more accurate answer than scope patterns do, and like I say, you’re rolling the dice if you’re not covering all of your bases every time. I definitely categorize this test as a novelty
I hook the pico leads up backwards so peaks are compression. I also don’t ac couple, I also zoom the waveform from the bottom left x1 to x10. I also add a filter on the channel which gives me pretty much same waveform as a amp clamp.
Cody’s Auto Diagnostics I like the idea of switching the leads, that caught me out while I was doing it 😂. I will have a go with the zoom, but not sure the mighty 2204A is up to it! It doesn’t have the filter function either. I think this is the best we can get with this scope, which is a good case for the 4425. Thanks for watching!
Mechanic Mindset oh that’s right I forgot the 2204a doesn’t have the zoom like that. Still a great tool and your probably right that’s the best that scope can do for voltage anyway
Great video
Glad you enjoyed it!
thank for video
Glad you enjoyed it!
Great video Darren 🙌... I’ve used the Pico diagnostic software without the amp clamp when I didn’t have the amp clamp which was fine ... now I use the amp clamp with the Pico 6 software it gives you more flexibility in changing settings ... what’s your preferred method ? Cheers 👍👍👍
Thanks Igor! I think with the higher spec and 4425A scopes, the voltage method would be ok. Not sure the 2204A is up to it. But I think amp clamp for me - easy! 👍
Very cool! How would you set it up to have an ignition trace on cylinder 1 as well? I just bought this scope and am curious about how to set that up
You could use a pick up to indirectly see ignition coil EMF. Or you could probe directly in to coil (might need an attenuator). Or use an amp clamp on the coil 👍
Turning on active noise filtering will help out with all the noise. I've used voltage for relative compression for years with good results.
Definitely 👍 What oscilloscope are you using. Unfortunately the feature isn’t available on the 2204A
@Mechanic Mindset I am using the newer Pico 4225a with BNC + with Pico software v7
So i just got my pico scope and i noticed theres a small switch on the side of the probs resting at x1 vs x10. Just wanted to make sure i wanted to use it to test canbus systems should i put it on x1 or x10 ? Thanks.
Btw i enjoy your videos man keep up the hard work 👍👍👑
Cheers! You don’t need to use the x10 switch for CAN bus. It basically allows you to measure x10 the input range of the scope (so up to 200V for a 2204A). Electronics engineers will also use this setting for measuring high frequency signals 👍
@@MechanicMindset have a blessed day thanks
Perhaps use a shunt to detect voltage variations. Less noise as well.
Nice idea, will have to look up high current shunts
Hey, Darren I did the check the way you did it and my waveform is not as clear as yours. Could that be the probe that I am using? I am using the one that comes with the pico 2204A scope.
Should still work. Try adjusting Vertical Resolution Enhancement in the channel setting. In DSP on Pico 7
@@MechanicMindset I have a high amp clamp from AESWAVE and I get a better picture with it. Love your channel. It helps me a lot with my little scope. Thank you for that.
Where does that AC voltage come from? Starter motor back EMF?
Thank you in advance for your answer.
It’s the fluctuation in battery voltage as the starter battles compression when the engine turns. Super accurate measurement!
@@MechanicMindset Thank you for the reply.
love your vieos.
Maybe a low pass filter will help for a better waveform
radu If the scope has it, that will help for sure. The more expensive scopes have that feature, but this base model 2204A doesn’t. Thanks for watching!
🤙🤙
You know the one biggest annoying this I find is the amp clamps need bloody batteries. Like a scan tool which can't take the power to charge itself from pin 16 OBD. Screwed if you don't have a power source. Luckily though I got a jump pack with a cigarette lighter hole. So can charge scan tool. Also got an inverter in the van 1600 watts to power a battery charger to keep vehicle properly juiced too. Yesterday trying to get a relative compression test done on my Autel Ultra and the green channel B which it was connected simply flat line at 0. Doing nothing. Its only today mechanic mindset said something and it triggered my thoughts. obviously it aint got a battery in it.
I just bought some 9v batteries that you can charge with a usb cable! Will show you soon 👍
Well from now on its the amp clamp.
Yeah same. Although I want to figure out why. I can’t put the blame on the 2204A!
Mechanic Mindset the 2204A is the same scope I use daily and it’s great to see these used in the field. I simply don’t have $1500US laying around for the automotive version at this time. Your videos show these can be used in the field for most applications.
Next time show were the flat spot was in the video. I had a pause and look at a few times to see. Just some information that would be helpful if you marked it in red. But the video was great otherwise. Thank You
Thanks for the feedback 👍
There's too much noise to see any difference. A low-pass RC filter should output the same inverted curve as your clamp probe. Try with a 10KΩ resistor / 1.5 µF capacitor to flatten frequencies over 10Hz.
Ah ok, will give it a go one day. Do you think using a band pass math channel would help? Or need the proper low pass filter?
@@MechanicMindset The result from the band pass math channel should match an RC filter if the sample rate for the selected time-base is high enough to correctly acquire the noise on top of the signal. If not, then it won't help.
@@florentbr83 Thought provoking! Thanks 👍
You know the one biggest annoying this I find is the amp clamps need bloody batteries. Like a scan tool which can't take the power to charge itself from pin 16 OBD. Screwed if you don't have a power source. Luckily though I got a jump pack with a cigarette lighter hole. So can charge scan tool. Also got an inverter in the van 1600 watts to power a battery charger to keep vehicle properly juiced too. Yesterday trying to get a relative compression test done on my Autel Ultra and the green channel B which it was connected simply flat line at 0. Doing nothing. Its only today mechanic mindset said something and it triggered my thoughts. obviously it aint got a battery in it.
Happens to the best of us James 🤣