At 4:52, you mention pulling out the fuse for the fuel pump for the static compression test, which I understand is to prevent fuel from entering the engine. However, at 7:29, you say to put the fuse back in for the running compression test. Won't having the fuel pump running during the running test still risk damaging the engine? Can you clarify why it's safe for the running test but not the static test? By the way, I really like the video-it's very informative!
He replied in a comment below clearing it up: "We didn't capture it but the fule injector should be disconnected to prevent fuel entering the cylinder while doing a running compression and snap compression test. Great question."
You said NOT to have the fuel injectors running because it could damage the cylinder walls so did you cut the fuel to just this one cylinder for your 'running' test?
The fuel pump is what pushes the fuel through the lines and to the injectors. The fuel pump is off cause he pulled the fuse. So no fuel is moving in the lines or going to any of the cylinders.
He replied in a comment below clearing it up: "We didn't capture it but the fule injector should be disconnected to prevent fuel entering the cylinder while doing a running compression and snap compression test. Great question."
I occasionally use my compression tester as a fuel pressure gauge, the 14mm long fine threads fit most fuel rails. Haven’t had any issues with o-rings, had this gauge since 1978, lol 😂
You probably didn’t get an accurate reading on your first static test because you didn’t hold the throttle open to ensure maximum airflow into the cylinder
8 have a v8 L92 (LS) engine, though my question is more general in nature: if you run a compression test with the engine running as you are in one stage of your video, how do you ensure that the injector isn't flooding the cylinder you are testing ? (since it doesn't have a plug in it, it won't fire but the injectors are still pushing fuel.
I don't understand. First you said we pull the fuse for the fuel pump because we will damage the engine if it is left in and then we put it back in and run the second test. Why does the 2nd test not damage the engine, get gas in the crankcase, etc.? What am I missing here?
We didn't capture it but the fule injector should be disconnected to prevent fuel entering the cylinder while doing a running compression and snap compression test. Great question.
I have a strange issue with my engine Min sped for hot compression test is 133 standard value is 188 My tests are #1 130psi #2 133psi #3 140psi #4 136psi My leak down test is #1 24% (rings) #2 10% (rings) #3 10% (rings) #4 14% (rings) I'm trying to figure out why my compression is kinda low on all cylinders but the leak down test is in spec
I'm kind of confused, you mentioned not too keep the fuel fuse in because it would wash the cylinder walls. Wouldn't that do that on your Running Comp test when you put the fuse back in?
Me neither, but he could’ve easily disconnected the fuel injector from #3… This a GDI engine? Those pump a lot of pressure (~1500-3000 psi) directly into the combustion chambers, I know it’s definitely something to consider when working with GDI engines.
I have combustion gases in my coolant I used a block tester . Everyone says blown had . But my car isn’t over heating and I don’t have smoke coming from my engine . Coolant keeps getting low. Can’t find any leaks outside . Hoses look good . Oil looks clean . Is this a test I need to check?
yep, I gotta remove the exhaust manifold to get to three of the cylinders. Can I run the engine for the second two tests without exhaust connected? Great video. Cheers & Thanks.
At the beginning he wisely defeated the fuel delivery for the static test. Later he put the fuel pump fuse back in but then did not disable the injector for the cylinder he was testing. This could explain why he didn’t get the 50% number he was expecting.
How did you connect the gauge during the running test? Was it still screwed into the spark plug hole? Did you disconnect the fuel injector electrically? How did you keep fuel out of the cylinder?
Question: If you don't want fuel building up in your cylinder and gauge during the static test, how do you keep that from happening when you perform the 2 other tests?
I thought it's a requirement to remove all spark plugs when do compression test? I suppose it can't work if we are looking for a comparative data between all cylinders.
You’re correct- to get comparative readings on a static compression test you have to remove all spark plugs. You also need to hold open the throttle blade or remove the throttle body to get maximum airflow in the engine for all cylinders
I ALMOST agree with you except that this video contains ABSOLUTELY NO EXPLANATION of what the "Snap" test is. He's just holding the gauge and then he's like "see?" Um no. I don't see. I don't see or hear ANYTHING about what a snap test is that you just performed
Many vehicles mostly fours have rail cops rather than individual cops, how would you take more than a static compression on those vehicles? The only workaround I could think of is just sticking wires on the plugs and running them into the coils but that surely impacts performance in a way that is unacceptable for valid data.
Hi Master Auto Training, Thank you for the nice video. In the 2nd test, i.e. the running compression test, after putting the fuse back, will it cause the problems you mentioned earlier when you explained why you needed to disconnect the fuel?
During Snap Test: what pressure reading will you get? Let’s say if EXHAUST WAS RESTRICTED instead of low pressure of 100psi from intake or exhaust valves than 116psi. 😮 10:13
That’s dependent on the engine. It’s always best to test a known good vehicle and begin to build your data base. Most manufactures no longer give us that spec in service information.
You can but without a dynamic (running compression) you’re not testing the engines ability to breathe and exhale (volumetric efficiency). Wont be a complete test if you skip running.
I'm kind of confused, on the 2nd test you put the fuse back , I thought the fuse wasn't supposed supposed to be in because of fuel going into the piston washing the cylinder walls
Good video but I do have a question, if you disable the fuel for the static test so it doesn't damage the rings and cylinders wall then what's keeping it from damaging the cylinder when the engine is running and you are testing it?
It's not about whether it's causing damage. It's about the fact that if fuel is being sprayed into cylinders being tested it'll effect the reading. It'll likely do one of two things. It's going to wash away anything inside the cylinder and get between the piston rings and the walls. Or the gas will act as a barrier sealing any loose gaps between the piston rings and the wall. That why there's dry compression tests, which is what he just did. And a wet compression test. Had he not diagnosed the issue using his method. The next step would've been pouring a small amount of oil into the cylinder (wet compression test) to see if it raised the pressure. The reason for this is that if you have bad rings, piston, or cylinder walls the oil will seal any gaps. If the compression doesn't change at all but is still low. That confirms that it's valves.
Unfortunately a cranking compression test is called a static test. “Begin with a normal ("static") compression test on a warm engine to eliminate obvious problems such as badly worn rings, burnt or bent valves or holes in pistons.” - AllData
If compression is low on that cylinder, spray some oil down in that cylinder. Re do the test. If it's piston ring wear, it'll read better for the time that oil is in there filling in the gaps. If it makes no difference, it's not ring related.
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Good video, but the generic music is very annoying and distracting.
At 4:52, you mention pulling out the fuse for the fuel pump for the static compression test, which I understand is to prevent fuel from entering the engine. However, at 7:29, you say to put the fuse back in for the running compression test. Won't having the fuel pump running during the running test still risk damaging the engine? Can you clarify why it's safe for the running test but not the static test? By the way, I really like the video-it's very informative!
I had the same question.
I have exactly the same question.
Yes exactly same question
He replied in a comment below clearing it up: "We didn't capture it but the fule injector should be disconnected to prevent fuel entering the cylinder while doing a running compression and snap compression test. Great question."
Very good explanation,thank you dear
You are welcome 😊
Excellent presentation. Your communication skills are great.
Always wanted to learn automotive technology. I am electrician by trade.
When you did the compression test - I noticed you only pulled the the one coil ,plug and not the rest of the coils ,plugs
Thanks my brother.... al be doing my Exams tomorrow... on how to test compression
You said NOT to have the fuel injectors running because it could damage the cylinder walls so did you cut the fuel to just this one cylinder for your 'running' test?
The fuel pump is what pushes the fuel through the lines and to the injectors. The fuel pump is off cause he pulled the fuse. So no fuel is moving in the lines or going to any of the cylinders.
Im kind of confused, you mentioned not too keep the fuel fuse in because it would wash the cylinder walls. Wouldnt that do that on the 2nd test ?
Agreed. I’m wondering if he disconnected the power from the fuel injector and just forgot to mention.
Yes I notice that too
He replied in a comment below clearing it up: "We didn't capture it but the fule injector should be disconnected to prevent fuel entering the cylinder while doing a running compression and snap compression test. Great question."
I occasionally use my compression tester as a fuel pressure gauge, the 14mm long fine threads fit most fuel rails. Haven’t had any issues with o-rings, had this gauge since 1978, lol 😂
Mine was cheap as possible like $25 came advertised as doing fuel, vacuum, and compression.
On a 2012 Toyota Corolla S for a static test when I crank it should I hold the gas pedal down? (I removed the fuel injector fuse)
Yes.
2:48 match up spark plug and compression gauge adapter length
5:25 clear flood mode (throttle pedal floored down all the way) , only some vehicles(?)
These are some of the best automotive mechanic tutorials online. Thanks!
Wow, thanks for watching and for your comment! 😁
You probably didn’t get an accurate reading on your first static test because you didn’t hold the throttle open to ensure maximum airflow into the cylinder
Thank you for your efforts , what about dray and wet tests. Is it like static one ?
I was told to take the coil wire off my distributior cap also. I have a 95 VW . Is this true?
You can also do that or ground one by one cylinder.
8 have a v8 L92 (LS) engine, though my question is more general in nature: if you run a compression test with the engine running as you are in one stage of your video, how do you ensure that the injector isn't flooding the cylinder you are testing ? (since it doesn't have a plug in it, it won't fire but the injectors are still pushing fuel.
I don't understand.
First you said we pull the fuse for the fuel pump because we will damage the engine if it is left in and then we put it back in and run the second test.
Why does the 2nd test not damage the engine, get gas in the crankcase, etc.?
What am I missing here?
We didn't capture it but the fule injector should be disconnected to prevent fuel entering the cylinder while doing a running compression and snap compression test. Great question.
@@MasterAutomotiveTraining Thank you for being so responsive and creating such helpful videos.
@@DanielDroegeShow You are very welcome, thank you for watching!
@@MasterAutomotiveTrainingThat's the answer I expected... after I posted the same question. Thank you.
I have a strange issue with my engine
Min sped for hot compression test is 133 standard value is 188
My tests are
#1 130psi
#2 133psi
#3 140psi
#4 136psi
My leak down test is
#1 24% (rings)
#2 10% (rings)
#3 10% (rings)
#4 14% (rings)
I'm trying to figure out why my compression is kinda low on all cylinders but the leak down test is in spec
Thank you, this was very helpful. I appreciate the words you gave to articulate your point.
I'm kind of confused, you mentioned not too keep the fuel fuse in because it would wash the cylinder walls. Wouldn't that do that on your Running Comp test when you put the fuse back in?
Yeh makes no sense
Washing those walls running all the fuel in cylinder 3 😂
That's what I'm saying, I don't think I've ever seen someone check the compression while engine is running.
Me neither, but he could’ve easily disconnected the fuel injector from #3…
This a GDI engine? Those pump a lot of pressure (~1500-3000 psi) directly into the combustion chambers, I know it’s definitely something to consider when working with GDI engines.
I was thinking same thing, a better explanation would be nice
I have combustion gases in my coolant I used a block tester . Everyone says blown had . But my car isn’t over heating and I don’t have smoke coming from my engine . Coolant keeps getting low. Can’t find any leaks outside . Hoses look good . Oil looks clean . Is this a test I need to check?
Does your car have an EGR cooler? th-cam.com/users/shortsOCKY0ew_oHY?si=H2BJzzIycjAiqJpK
Do you have remove all the spark plugs to do a compression test or one at a time?
If you are doing a cranking compression all off, running compression only the cylinder you are testing.
yep, I gotta remove the exhaust manifold to get to three of the cylinders. Can I run the engine for the second two tests without exhaust connected?
Great video. Cheers & Thanks.
Yes you can run quickly without exhaust manifold, make sure to wear ear protection as it will be super loud.
It's good to protect your hands using gloves, what about cleaning out the spark plug Wells before removing spark plugs??
Bro, this was an awesome video!!
Thanks for sharing your knowledge👏🏽👏🏽👏🏽👏🏽👏🏽👏🏽👏🏽
Seems like you may have forgotten to disable fuel delivery to that cylinder after reinstalling the fuel pump fuse? Otherwise, great tutorial video!
What do you mean by that?
At the beginning he wisely defeated the fuel delivery for the static test. Later he put the fuel pump fuse back in but then did not disable the injector for the cylinder he was testing. This could explain why he didn’t get the 50% number he was expecting.
@@MartinWibertI was thinking the same thing. He never went over if he did or didn't, and I suspect he didn't.
How did you connect the gauge during the running test? Was it still screwed into the spark plug hole? Did you disconnect the fuel injector electrically? How did you keep fuel out of the cylinder?
Question: If you don't want fuel building up in your cylinder and gauge during the static test, how do you keep that from happening when you perform the 2 other tests?
It's a great tutorial video, informative and self-explanatory., you make it so easy to understand. Very happy
I've always worn gloves but lately been raw dogging it brosky😂.thanks for info some of us don't have time for school
I thought it's a requirement to remove all spark plugs when do compression test? I suppose it can't work if we are looking for a comparative data between all cylinders.
You’re correct- to get comparative readings on a static compression test you have to remove all spark plugs. You also need to hold open the throttle blade or remove the throttle body to get maximum airflow in the engine for all cylinders
thats why you cut off the fuel
wheres the link in the description for the compression worksheet download?
Oops…… here it is drive.google.com/file/d/1ffDlHM26EwTHvJf45JBfphKzt5NGkD5r/view?usp=drivesdk
Wow very good instructional video. You've earned my sub because of how informative this is and I don't just subscribe to any TH-cam video. 🧐🤔
My engine is overheating and I can't do a running compression test because if it get too hot, I don't want to damage the engine. Any suggestions?
Harbor freight, got a kit for 30 dollars
Thanks
I don't understand why you are not open fully throttle valve ,when you undergoing static compression test ?
You rock ❤
How can you do a running test if your coil pack is all one piece for all cylinders?
Both this and the leak down video are good straight to the point no extra bs. I really appreciate it
I ALMOST agree with you except that this video contains ABSOLUTELY NO EXPLANATION of what the "Snap" test is. He's just holding the gauge and then he's like "see?" Um no. I don't see. I don't see or hear ANYTHING about what a snap test is that you just performed
Great refresher, Thanks!
Thank you teacher with you I will be perfect.
Many vehicles mostly fours have rail cops rather than individual cops, how would you take more than a static compression on those vehicles? The only workaround I could think of is just sticking wires on the plugs and running them into the coils but that surely impacts performance in a way that is unacceptable for valid data.
Nice explanation and pace, I'll be doing this on my car once my kit arrives
Thanks so much brother. Very well explained
Hi Master Auto Training,
Thank you for the nice video.
In the 2nd test, i.e. the running compression test, after putting the fuse back, will it cause the problems you mentioned earlier when you explained why you needed to disconnect the fuel?
During Snap Test: what pressure reading will you get? Let’s say if EXHAUST WAS RESTRICTED instead of low pressure of 100psi from intake or exhaust valves than 116psi. 😮 10:13
great video!
Thank you, Glad you enjoyed it
How much compression pressure should be in petrol engine and diesel engine
That’s dependent on the engine. It’s always best to test a known good vehicle and begin to build your data base. Most manufactures no longer give us that spec in service information.
Awesome videos !!
Is that an ice cream truck playing music in the background?
He passes by everyday 😂
My compression test only got 40 lbs cylinder 3 the other 3 cylinders had like 160 do you think maybe bad valve
Muy buen video profe Óscar. Saludos
Saludos Benito!
Where should I connect the oil pressure gauge in m271?
I'm about a year and a half deep into being a dealership technician and I highly appreciate your videos
You are welcome and thank you for your support!
What do you do with a mechanical fuel pump. Meaning, disable it. I suppose I could disconnect the fuel line from the carb?
Can I just do a static test to check compression?
You can but without a dynamic (running compression) you’re not testing the engines ability to breathe and exhale (volumetric efficiency). Wont be a complete test if you skip running.
I'm kind of confused, on the 2nd test you put the fuse back , I thought the fuse wasn't supposed supposed to be in because of fuel going into the piston washing the cylinder walls
Great video professional content
Thank you for watching!
So when doing a running test. You disconnect power supply injector.
I understand this but I don’t..lol I’ll leave it up to you the mechanic to figure my car out !
Great vid brother Oscar... And the new intro kicks ass!
Thanks Zach!
Please what about the ignition coil, should the connector removed
I see some people crank the cars until the needle stops then takes a compression reading
😎👍 Hemoso y hútil video, estoy aumentando mis conocimientos Gracias. 😎👍🤚👋
Good video but I do have a question, if you disable the fuel for the static test so it doesn't damage the rings and cylinders wall then what's keeping it from damaging the cylinder when the engine is running and you are testing it?
It's not about whether it's causing damage. It's about the fact that if fuel is being sprayed into cylinders being tested it'll effect the reading. It'll likely do one of two things. It's going to wash away anything inside the cylinder and get between the piston rings and the walls. Or the gas will act as a barrier sealing any loose gaps between the piston rings and the wall. That why there's dry compression tests, which is what he just did. And a wet compression test. Had he not diagnosed the issue using his method. The next step would've been pouring a small amount of oil into the cylinder (wet compression test) to see if it raised the pressure. The reason for this is that if you have bad rings, piston, or cylinder walls the oil will seal any gaps. If the compression doesn't change at all but is still low. That confirms that it's valves.
Thank you. That's very informative.
What if the cylinder is under the intake near the fire wall?
Like it good
I'm glad you like it, thank you.
Otro good video oscar saludos
Muchas gracias saludos
very helpful and in depth
Shame on you meter reading is not shown well in camera.
Thts a bit harsh
your first test is dynamic NOT static compression!!
Unfortunately a cranking compression test is called a static test. “Begin with a normal ("static") compression test on a warm engine to eliminate obvious problems such as badly worn rings, burnt or bent valves or holes in pistons.” - AllData
Good video well
Explain and detail
Thanks for sharing
wonderful tests
How to test if oil rings are worn or damaged?
If compression is low on that cylinder, spray some oil down in that cylinder. Re do the test. If it's piston ring wear, it'll read better for the time that oil is in there filling in the gaps. If it makes no difference, it's not ring related.
Why do people play music in instructional videos? I had to turn off this video because the stupid rock music in the background.
MERICA!
You showed a prepared record sheet (form)... Any recommendations for where a shop can aquire various forms for testing and record keeping?
Worksheet is here: drive.google.com/file/u/6/d/1ffDlHM26EwTHvJf45JBfphKzt5NGkD5r/view?usp=drivesdk