Alright dude i have a few things to add because you may be leading some people astray. Like me. So first of all your vacuum reading depends entirely on your Barometric Pressure/Elevation. At or close to sea level you should see a vacuum of 17-22 in/Hg. That number decreases as you go up in altitude (down in barometeric pressure). So at 3-4 thousand feet you should see a vacuum of 15-19 in/Hg. I am at 7,000 ft above sea level, my Vacuum should read 12-16 in/Hg. Keep in mind that Idle vacuum for most engines is about 18-22 in/Hg AT SEA LEVEL but some may produce only 15-17 inches idle depending on your motor. you need to refer to your cars repair manual for vacuum specs. If your valve timing is retarded, the needle on the guage will bounce due to blow by on the intake valves back into the manifold........ not a steady low pressure reading on the gauge. Under load your Vacuum should be zero at cruising speed thats how you know you have a healthy motor.
Great point Josh! What is the formula for determining vacuum at various elevations? I'm at 5K ft. here in Colorado maybe it should be between 13-18 In/Hg?
Nope, at full throttle on a gasoline engine the vacuum will be at or near (filters have some restriction) 0. any time you're not flooring it, that throttle valve is closing in order to create a partial vacuum in the intake manifold (this is how your car restricts the amount of air it ingests).
Good trivial point, if using an actual mercury gauge (which almost no one owns) which measures pressure differential. But not at all related to this regardless of gauge. Please note that there is an acceptable range. This covers pressure differences. Please also consider that the external pressure will have no effect on fluctuations or trends, which are what we look for in diagnostics.
I am fully trained auto and diesel mechanic, since I started repairing cars and trucks especially gasoline engines I use vacuum gauge for diagnosing engine troubles.I appreciate your excellent demonstration.
This is by far the most simple to the point video that was so helpful and educational! Thank u for making this video and hope more people pay attention to your open your mind video.. thanks
Just purchased this gauge to check vacuum and fuel pressure wow so helpful it all makes sense but you don't think about it until someone tells you, great video mate
This is the exact thing I was looking for great video IAM a Old school mechanic and a lot of New mechanic do do this kind of diagnostics but I am learning really fast about it THANK YOU GOD BLESS
hi, i was hoping you could help me with the readings i got from my little mazda truck 2bbl. the needle from my vac gauge reads in between 15 and 18 unsteady. i could never get it to hit 20 in of mercury. when i rev it up, it would go back to 0 and then goes to 20 and then back to 15-18.
its the best, to the point video on subject....covers each and every defect that a vacuum guage can detect....yes, it doesn't discuss why part but at the same time, gives you clear lines hiw to interpret the guage readings....❤❤❤
That sound like providing food, when your're thirsty! LOL 😂 All in all very nice but don't fulfill the necessary requirements. Compression test, leak down test, vacuum test. They all have a place and time to be done and work as complements rather than substitutions of each other! Cheers
Me es de mucha utilidad éste video, gracias por compartir tu conocimiento. Recibe fuerte abrazo y saludos desde la ciudad de Tampico Tamaulipas México. Gracias.
Dude, I do love your explanations here on what can be seen with such a guage when you know how to read it and what the reading means. It's crazy how very few mechanic just don't the easy steps to properly diagnostise an engine with the proper tools to fix the right thing once and for all. Same goes with multimeters and voltage drops across the starter, block or alternator cables. I've seen stupid mechanic screaming after the parts guy that his last 3 starters were worn and a bad connection that couldn't be seen bared eyes was the problem of slow cranking... again, i can't wait to get a hand on a vacuu, gauge and fix my engines myself better. thanks a lot for this helpful video
Good video. I have the symptoms of an exhaust obstruction. Strong 20 inches, then as I throttle up (in park, no load) it starts to sputter and loses vacuum. It a simple v8, Oldsmobile 307 but it been troublesome. I’ve been through multiple sets of plug/ wires and distributors. New fuel pump filter even overhauled the motor. I guess I’m gonna check the fuel pressure tomorrow . Oh and I have no exhaust restriction. But maybe I have carburetor problems. I don’t know what else it could be.
Big thanks for the explanation! On my 350 sbc I read at idle a flickering needle on 16hg at 600rpm. Fast idle 1200rpm and the needle is steady at 19hg. Timing is late 8 degree. I think it‘s a mix from bad valve stem seals, that also indicat the blueish puffs after a shifts and a bit more timing mabye 12 degree? Thanks
forgot most important step - what cam do you have? stock/stage 1 this would apply, but id drop 2-3 inches per stage of cam, around stage 3 the readings get more whacky from a bad vac signal. My 288HR comp cam idles 7 inches and very few of these principles apply with radical cams. Id say around 230-240 duration and up things start falling apart.
17 - 20 Hg's for an engine with a stock OEM cam. If you have a more radical cam vacuum will be lower. In my case with a .610 lift my vacuum reads around 13 Hg's at idle then drops to 0 at high RPM.
Nice video thanks. I'm weighing a valve adjustment on my Sentra B15 because of low acceleration chatter - I'll see if I can get any clues w/ this Harbor Freight tool tomorrow. By the way, I've been able to thread the hose under the hood and place the gauge on the windshield so that I can view it when performing snap-throttle. If it''s too short for your location just go to the auto parts store and buy a 2' section of comparable vacuum line (take the original for comparison).
I'm having this done today on.my 98 dodge ram 5.9l w/ 187,000 "ticks on the clock." This explains alot for me to know if I need a rebuild or not, thanks!
Nice video about probably the most forgot and underrated cheap tool to have in your tool bag. Most nowadays think it's not worth because it lacks blinking lights or a PC attached. LOL ;-) Thumbs up
Hi Matt, fantatic video! Been watching several videos: all articulately explained and videod (not easy to do). I have the feeling that if I keep watching, I could be a professional. Good job! God bless!
Thanks for the great video! I have a 351M in a 78' F250, that starts to have white smoke after warming up, but not on first starting. After watching your video I bought a gauge and the reading on start up is a vibration between 15-16 and then after warming up, it fluctuates between 6-20. Do you think I have a head gasket leak?
awesome awesome awesome video !!! Ignore any naysayers. Anyone can be a critic (really? I should account for barometric pressure? How about humidity? How about durometer rating of the line? Sheesh) I have a 1966 Mustang 289 4 barrel and I get good vacuum but have that very fast small fluctuation. SO not sure if its valve seals or as you pointed out to someone else, new, so don't worry...BUT ...changing to aluminum heads soon so I will worry then...thanks for a great video
okay, I have a doubt, I'm using a longer vaccum hose for fuel pressure regulator than the stock length, what happens if I cut and make it shorter to connect into the intake? how the engine respond with a shorter vacuum hose and it's fuel relation? An advice or suggestion would highly appreciated. Thanks.
Great video Mat Motorz, thanks. Josh Arbour, I presume pressure gauge shown measures relative pressure(1), therefore altitude of engine is irrelevant for this analysis. (1) pressure gauge indicates zero when not connected at all altitudes
Lets do some math on this. At sea level atmosferic pressure will be 100 kpa or 29.9 in Hg. We can asume we live in a city at an altitude of 4000mts Over sea level. Over there armosferic pressure will be little more than 60k Kpa equivalent to 18 in Hg. With 18 in of armosferic pressure how can you get 22 in of vacumm. I believe Josh is right.
Everything is new in my 68 Mustang, with a crate stock 302, runs well no issues. But the vacuum gauge shows 15. I managed to get 17 after advancing the ign. timing a little. What do you think? Should I advance it further to achieve 18 or more?
4:51 ...okay wait, so the declining gauge pressure is a sign of both an exhaust obstruction AND an air leak in the in the intake manifold? also, if you disconnected one of the vacuum hoses, what is plugging up the port that you disconnected it from?
Vacuum guage and stethoscope.. two of the simplest but most useful tools. Most vacuum gauges come with a piece of paper that outlines these readings also.
Hey MattsMotorz. Nice video. Appreciate the info! The line youu stuck the cone into, was that going into the intake? Or where was the other end at? I got a 2.4l gm motor. It's the ecotec and has dbw, no throttle cables. But anyway, I couldnt tell if the end you put the cone into was the hose end that came OFF the manifold or does the other end of it go TO the manifold? I'm lil confused to say the least. I sort of wish you'd go over some different hoses to use and how to hook up the vac gauge. Like with that "t" you had and any other ways to hook up the vac gauge. But ex video, real useful for me!!
Great video. There's a lot to remember- there was a mistake. This it critical so perhaps have the info written down to refer to in the future. Good though.
Superb explanation I just learned a lot from this vedio.can you please do a vedio on Dry and Wet Compression test and cylinder leakage testing.if you have time.
Hi my trucks been sitting for a year untouched ,diesel Hilux Rebuilt engine ,brake boosters not working but I have a new vacuum pump and it registers at 25-6 very steady inches of mercury (300m above sea level ) I do remember the first day I installed the engine I had brakes only ran it for a couple of minutes next morning nothing ,pedal doesn't move at all when turned on ,is it possible the diaphragm weakened over that time
Hi thanks for the video. Should we tap the gauge before the throttle body valve? I am asking because my car has 2 hoses tapped off the intake boot. One hose goes to the brake booster and the other hose goes to fuel pressure regulator. I connect the gauge to one of these hose and there is no vacuum at all (maybe too little). I think it is reasonable since those hoses are close to air entrance (air filter), which is a big door. But I re-think if there is no vacuum how the brake booster and fuel pressure regulator work.
You need to connect to a vacuum source directly off the intake manifold. The brake booster is a great place to tap into because it has full engine vacuum.
When your doing these readings. Is it good to turn all Accessories off? Soon as my compressor comes on my readings drop alot? Which seems normal. Am I wrong?
Alright dude i have a few things to add because you may be leading some people astray. Like me. So first of all your vacuum reading depends entirely on your Barometric Pressure/Elevation. At or close to sea level you should see a vacuum of 17-22 in/Hg. That number decreases as you go up in altitude (down in barometeric pressure). So at 3-4 thousand feet you should see a vacuum of 15-19 in/Hg. I am at 7,000 ft above sea level, my Vacuum should read 12-16 in/Hg. Keep in mind that Idle vacuum for most engines is about 18-22 in/Hg AT SEA LEVEL but some may produce only 15-17 inches idle depending on your motor. you need to refer to your cars repair manual for vacuum specs. If your valve timing is retarded, the needle on the guage will bounce due to blow by on the intake valves back into the manifold........ not a steady low pressure reading on the gauge. Under load your Vacuum should be zero at cruising speed thats how you know you have a healthy motor.
and the sentor MAP? what values this take?
Great point Josh! What is the formula for determining vacuum at various elevations? I'm at 5K ft. here in Colorado maybe it should be between 13-18 In/Hg?
Nope, at full throttle on a gasoline engine the vacuum will be at or near (filters have some restriction) 0. any time you're not flooring it, that throttle valve is closing in order to create a partial vacuum in the intake manifold (this is how your car restricts the amount of air it ingests).
@Andre Woods Advance Challenged maybe?
Good trivial point, if using an actual mercury gauge (which almost no one owns) which measures pressure differential. But not at all related to this regardless of gauge. Please note that there is an acceptable range. This covers pressure differences. Please also consider that the external pressure will have no effect on fluctuations or trends, which are what we look for in diagnostics.
I am fully trained auto and diesel mechanic, since I started repairing cars and trucks especially gasoline engines I use vacuum gauge for diagnosing engine troubles.I appreciate your excellent demonstration.
Awesome! Thanks for the comment.
I’ve spent 1+ hours trying to find a video of WHERE (and how) to hook up the vacuum gauge to, and you finally answered my question! THANK YOU!!!
This is by far the most simple to the point video that was so helpful and educational! Thank u for making this video and hope more people pay attention to your open your mind video.. thanks
Just purchased this gauge to check vacuum and fuel pressure wow so helpful it all makes sense but you don't think about it until someone tells you, great video mate
This is the exact thing I was looking for great video IAM a Old school mechanic and a lot of New mechanic do do this kind of diagnostics but I am learning really fast about it THANK YOU GOD BLESS
Exactly what I needed to see before heading back out tomorrow. Thanks
Thanks for very useful video. Every do it your self mechanic should have a vaccum gauge. Is this the civiv engine in the car?
Frugal a guy explained it without going to get McDonald's or driving talking shit . Thank you
Great video! I bought one of these gauges over 20 years ago but never really used it. Amazing what stories these gauges can tell.
Wow dude, did anyone tell you that you sound like Garth from "Waynes world"......Excellent video.
Helpful. I'm considering purchasing one of these to help diagnose but had no idea where to start with it or what to make of any observations.
Dear sir.ive just found this video.absolutety superb.very clear.
This has helped me loads.stevevfrom the uk.
Clear and to the point. I have a 55 side valve british truck. I'll buy one of these gauges.
Well damn if everything you claim is true then I have no reason to believe it's not This is a gold mine of info man I really do appreciate it
Very good! Such a simple tool yet often overlooked and one of the most useful in the arsenal!
hi, i was hoping you could help me with the readings i got from my little mazda truck 2bbl. the needle from my vac gauge reads in between 15 and 18 unsteady. i could never get it to hit 20 in of mercury. when i rev it up, it would go back to 0 and then goes to 20 and then back to 15-18.
great video, very well explained. I've just ordered one and now wonder why in 30 years of car tinkering I've never had one before
Vintage Steel same here should have bought one years ago. Very inexpensive tool to have.
its the best, to the point video on subject....covers each and every defect that a vacuum guage can detect....yes, it doesn't discuss why part but at the same time, gives you clear lines hiw to interpret the guage readings....❤❤❤
very informational. Doing a vacuum test seems alot easier than doing a compression test since sometimes the spark plugs are hard to get to
That sound like providing food, when your're thirsty! LOL 😂 All in all very nice but don't fulfill the necessary requirements. Compression test, leak down test, vacuum test. They all have a place and time to be done and work as complements rather than substitutions of each other! Cheers
Me es de mucha utilidad éste video, gracias por compartir tu conocimiento.
Recibe fuerte abrazo y saludos desde la ciudad de Tampico Tamaulipas México.
Gracias.
Dude, I do love your explanations here on what can be seen with such a guage when you know how to read it and what the reading means. It's crazy how very few mechanic just don't the easy steps to properly diagnostise an engine with the proper tools to fix the right thing once and for all. Same goes with multimeters and voltage drops across the starter, block or alternator cables. I've seen stupid mechanic screaming after the parts guy that his last 3 starters were worn and a bad connection that couldn't be seen bared eyes was the problem of slow cranking... again, i can't wait to get a hand on a vacuu, gauge and fix my engines myself better. thanks a lot for this helpful video
Great information!!! has come in handy multiple times!!! Thanks!
Good video.
I have the symptoms of an exhaust obstruction. Strong 20 inches, then as I throttle up (in park, no load) it starts to sputter and loses vacuum. It a simple v8, Oldsmobile 307 but it been troublesome.
I’ve been through multiple sets of plug/ wires and distributors. New fuel pump filter even overhauled the motor.
I guess I’m gonna check the fuel pressure tomorrow . Oh and I have no exhaust restriction. But maybe I have carburetor problems. I don’t know what else it could be.
Big thanks for the explanation! On my 350 sbc I read at idle a flickering needle on 16hg at 600rpm. Fast idle 1200rpm and the needle is steady at 19hg. Timing is late 8 degree.
I think it‘s a mix from bad valve stem seals, that also indicat the blueish puffs after a shifts and a bit more timing mabye 12 degree? Thanks
Class video, clear and concise with no fluff
forgot most important step - what cam do you have? stock/stage 1 this would apply, but id drop 2-3 inches per stage of cam, around stage 3 the readings get more whacky from a bad vac signal. My 288HR comp cam idles 7 inches and very few of these principles apply with radical cams. Id say around 230-240 duration and up things start falling apart.
17 - 20 Hg's for an engine with a stock OEM cam. If you have a more radical cam vacuum will be lower. In my case with a .610 lift my vacuum reads around 13 Hg's at idle then drops to 0 at high RPM.
Nice video thanks. I'm weighing a valve adjustment on my Sentra B15 because of low acceleration chatter - I'll see if I can get any clues w/ this Harbor Freight tool tomorrow. By the way, I've been able to thread the hose under the hood and place the gauge on the windshield so that I can view it when performing snap-throttle. If it''s too short for your location just go to the auto parts store and buy a 2' section of comparable vacuum line (take the original for comparison).
I'm having this done today on.my 98 dodge ram 5.9l w/ 187,000 "ticks on the clock." This explains alot for me to know if I need a rebuild or not, thanks!
Great job. I really like how you explain how to read the vacuum gauge for different kind of engine problems. Thanks
Thank you for your clear explanations.Also for the captions, which made it easy for me to take notes. Good job!
I did some research and found a gauge just like yours at NAPA. Wonderful! Thank you, David 🐈
They have that one at HF for about $13
Excellent video! This was a comprehensive explanation on how to use intake manifold pressure readings to identify engine issues.
Yeah but did he have to tap into the other end where he pulled the line off? I can't find where to try this on my 4.6
Nice video about probably the most forgot and underrated cheap tool to have in your tool bag. Most nowadays think it's not worth because it lacks blinking lights or a PC attached. LOL ;-) Thumbs up
So we just look at a nonmoving gauge and listen to you talk? Great video…
Thank You for this video. One of the best I've seen!
Hello do you have the link to where I can buy the cage? Or any recommend for good cauge?
This was very good, thank you. Its amazing the amount of troubleshooting that can be done easily with proper knowledge of this tool.
Good video,nice and clear and in plain English,really helpful,thanks.👍
I agree with plain English, thanks also for that. Great job to sharing this
Thank you for making this video. It was very informative and easy to understand ☆
real good vid thanks helps alot with my new engine in my 65 gto
Well done ! Good audio, easy graphics, concise script .
Question: Wouldn't not plugging the port on the intake manifold where you take the tube off of, affect readings since it is letting air in/out?
Amazing what you can tell about an engine from an analog gauge.
I have a steady 8 in of mercury on my 289. According to your video I have a big vacuum leak right?
Great video Thanks
Great video. It changed my life.
dude, I love how you explain things, thank you for taking the time to make the video, you truly have a knack for teaching
+gReGsKi GmAiL Thanks a lot!
awesome video....very informative ...thanks
Nice video mate, really helpful!
woah
Hi Matt, fantatic video! Been watching several videos: all articulately explained and videod (not easy to do). I have the feeling that if I keep watching, I could be a professional. Good job! God bless!
This is simple applicable and totally true
Thanks for the great video! I have a 351M in a 78' F250, that starts to have white smoke after warming up, but not on first starting. After watching your video I bought a gauge and the reading on start up is a vibration between 15-16 and then after warming up, it fluctuates between 6-20. Do you think I have a head gasket leak?
Excellent meticulous tutorial.
awesome awesome awesome video !!! Ignore any naysayers. Anyone can be a critic (really? I should account for barometric pressure? How about humidity? How about durometer rating of the line? Sheesh) I have a 1966 Mustang 289 4 barrel and I get good vacuum but have that very fast small fluctuation. SO not sure if its valve seals or as you pointed out to someone else, new, so don't worry...BUT ...changing to aluminum heads soon so I will worry then...thanks for a great video
okay, I have a doubt, I'm using a longer vaccum hose for fuel pressure regulator than the stock length, what happens if I cut and make it shorter to connect into the intake? how the engine respond with a shorter vacuum hose and it's fuel relation? An advice or suggestion would highly appreciated. Thanks.
Can you hook the vac gauge right on the side of the intake??,, My 2.0 Pinto reading is low, that's the place I see to hook the rubber hose into.
That's a car you rarely see anymore
Good video that is crazy I didn't know a vacum gauge could tell you all that.
Excellent Vid! I got exactly the info I was looking for. THANKS!
Dude! thumbs up for sure on a great video. Keep up the great work.
Great video Mat Motorz, thanks.
Josh Arbour, I presume pressure gauge shown measures relative pressure(1), therefore altitude of engine is irrelevant for this analysis.
(1) pressure gauge indicates zero when not connected at all altitudes
Lets do some math on this. At sea level atmosferic pressure will be 100 kpa or 29.9 in Hg. We can asume we live in a city at an altitude of 4000mts Over sea level. Over there armosferic pressure will be little more than 60k Kpa equivalent to 18 in Hg. With 18 in of armosferic pressure how can you get 22 in of vacumm. I believe Josh is right.
Thanks for great video. It is useful.
Excellent video!
Everything is new in my 68 Mustang, with a crate stock 302, runs well no issues. But the vacuum gauge shows 15. I managed to get 17 after advancing the ign. timing a little. What do you think? Should I advance it further to achieve 18 or more?
Very use and well explained. Thank you.
Thanks for very useful video.
best presentation ive seen
Thanks a lot for this very important video.
Great vidio Matt!!
Helpful information, thank you for sharing !!
Very helpful - great explanation!
hey my friend that is a great video I've learned a lot thank you very much
4:51 ...okay wait, so the declining gauge pressure is a sign of both an exhaust obstruction AND an air leak in the in the intake manifold? also, if you disconnected one of the vacuum hoses, what is plugging up the port that you disconnected it from?
Thanks MattsMotorz. Great video. Very informative. I have a vacuum gauge kit on order from Amazon after your video.
Good info in plain lingo,nice 1
+james woolley Thanks for watching!
Excelent ! Thanks for the video !
Please advise what is the normal vacuum pressure when the aircon is on and when its off? Thank you.
Vacuum guage and stethoscope.. two of the simplest but most useful tools.
Most vacuum gauges come with a piece of paper that outlines these readings also.
Very helpful!
Hey MattsMotorz. Nice video. Appreciate the info! The line youu stuck the cone into, was that going into the intake? Or where was the other end at? I got a 2.4l gm motor. It's the ecotec and has dbw, no throttle cables. But anyway, I couldnt tell if the end you put the cone into was the hose end that came OFF the manifold or does the other end of it go TO the manifold? I'm lil confused to say the least. I sort of wish you'd go over some different hoses to use and how to hook up the vac gauge. Like with that "t" you had and any other ways to hook up the vac gauge. But ex video, real useful for me!!
It went to the intake. You always hook up the gauge to a line that goes to the intake directly.
Great video. There's a lot to remember- there was a mistake. This it critical so perhaps have the info written down to refer to in the future. Good though.
Impressive video explanation
Is this is the same way you adjust and measure the fuel and air mixture?
Superb explanation I just learned a lot from this vedio.can you please do a vedio on Dry and Wet Compression test and cylinder leakage testing.if you have time.
I have a video on compression testing and leak down testing already.
Hi my trucks been sitting for a year untouched ,diesel Hilux
Rebuilt engine ,brake boosters not working but I have a new vacuum pump and it registers at 25-6 very steady inches of mercury (300m above sea level )
I do remember the first day I installed the engine I had brakes only ran it for a couple of minutes next morning nothing ,pedal doesn't move at all when turned on ,is it possible the diaphragm weakened over that time
This was just a great video!
Thanks!
This video was very helpful.
I have a Hiace with 2trfe. 2012 model. Im using torque pro and it shows my Vacuum constantly at a steady 25 at idle.
Everything seems to be healthy?
Thanks for a great video! And yes, I "Like" and I subscribed.
I appreciate it! :]
@@MattsMotorz hey Matt, great video. Question, how much vacuum should an engine be pulling, on a crank no start no spark condition?
Great video, thanks for sharing. I did the test and the neddle stays about 21, vibrating a little bit, what does this mean?
Sounds pretty normal and healthy to me!
Hi thanks for the video. Should we tap the gauge before the throttle body valve? I am asking because my car has 2 hoses tapped off the intake boot. One hose goes to the brake booster and the other hose goes to fuel pressure regulator. I connect the gauge to one of these hose and there is no vacuum at all (maybe too little). I think it is reasonable since those hoses are close to air entrance (air filter), which is a big door. But I re-think if there is no vacuum how the brake booster and fuel pressure regulator work.
You need to connect to a vacuum source directly off the intake manifold. The brake booster is a great place to tap into because it has full engine vacuum.
I’m just curious, why wouldn’t the tube be inserted into the manifold instead of the tube?
If you have doubts about where to plug it in, plug it into the line which is sucking air. That's the vacuum source you are going to read.
@@wymple09
Thanks Warren,
I did that, needle is in the green range, thanks very much.
excellent video
Where does that vacuum line come from
Hi, I live in Quito, 2.850 m over the sea. Please, can you tell me how much I can expect read at the vacuum gauge in my 383 stroker motor ?
What about catalytic converter isn't it a built in exhaust restriction? Should a car with cats drop to -5 during acceleration while not being faulty
Sir this vacuum Guage is used for efi car also or not
That was a great video man thanks!
Hi i did the test on my car en i noticed that with the ac on it stopped at 40 but with out the ac on was on green is that normal ? Txjx
When your doing these readings. Is it good to turn all Accessories off?
Soon as my compressor comes on my readings drop alot? Which seems normal. Am I wrong?