How to Use a Vacuum Gauge for Diagnostics

Back in the day a vacuum gauge was the primary diagnostic tool for your engine. Over time the vacuum gauge and how to use it have been forgotten. In this video our Moss Motors tech department gives insight and testing procedures on how to use this simple tool.

[@jbaudet]

Im not a mechanic by any means but this guy really has the ability to take a topic and make it understand, I fully understood everything he said, great explanation, great details and great tone of voice. Thanks

[@502deth]

the bob ross of engine repair.

[@btchhopperou812]

More like Mr. Rogers

[@nata911]

I'm 26 years old and have been into Japanese cars my whole life, I've never used a vacuum gauge to work on them nor did I ever know what one was for. my grandfather gifted me his old 68' dodge dart and I needed a vacuum gauge to set the idle mix screws on the carb. after watching your video I feel like I may be able to apply vacuum gauge diagnostics to a lot more than I once thought, from my 67 dart, to my 87' BMW, and my personal favorite my 07' Subaru. old mech vacuum gauges are valuable for any engine, because at the end of the day an engine is really just an air pump. Thanks for the video, I appreciate that you made it.

[@charlesdowns1691]

you should be able to set your carb by turning screws out around 2 turns out and then use vacume gadge to get highest reading with each screw +turn them in until gadge drops then back out about 1quarter turn. do this with both screws. then adjust curb idle to specs.

[@sexybluelady]

Hearing that dial up connection in the background, made me smile. It sent a little tingle up my arms, and made me think back to the days of AOL and waiting 20 mins for a page to load, and thinking that was "fast". Now people complain if it takes longer than a millisecond. Wow how times change. :-)

[@CPT115FA]

Sir... I truly appreciate your approach to teaching new motorheads, like me, about what means what. Keep these lessons, and style of teaching coming! ATW! Chris

[@poppagrouch4781]

Great information... I can't help but to think of Bob Ross at times while you talked...

[@1997LT1Camaro]

I really enjoy moss motors videos. Very well explained. Nothing like having a good teacher.

[@kevinthacker8349]

Been a cane diy mechanic, for years and that was very interesting and educational. Thanks

[@terrywin2661]

WOW!! As an amateur mechanic, this is some AWESOME information!! THANKS SO MUCH for sharing your knowledge in such a way that a beginner like me could easily digest it!!!

[@spelunkerd]

This is the best explanation of vacuum I have found on youtube. There's been a short lag in posting from MossMotors this month, and I'm glad to see more. Of course any test can lack specificity, and vacuum testing is no different. The hardest part for a neophyte is to get all the possible explanations in proper order, so the most common cause of a problem is investigated first. Thanks again.

[@JoeNunes345]

By the time that i watched 50% of this tutorial, i had realized that it was the best ever explanation that i had ever seen on the "underated use of a vacuum gauge". Would i be wrong in thinking that the same principles/tests could still be applied to modern engines? After all, what happens inside an internal combustion engine has not changed, but rather, it's how it happens that has changed, i think! Thank you very much, for a great video. Joe

[@henrykhachaturian8048]

Yes. You absolutely can use a vacuum gauge on a modern engine.

[@arthurmoore1524]

Yea you can use it on the new puny engines. Its less expensive than the cost of an automotive computer diagnostic tool, and just as, if not more effective. Maybe not efficient, but effective. A man tuning in the dessert would damn sure rather have a Guage than a computer where there's no internet nor man around who is a mechanic he can push his problem off on.

[@robotseattrees9386]

i have looked at pics of gauges i have done the forums on all the sights and this is by far the best explanation ive seen!

[@ChiefMovez]

Video of the year for me. I needed that.

[@george1la]

Very good direct simple important information. Thanks.

[@JohnG-sd1hx]

You are a great communicator and instructor! Thank You👍

[@train4905]

Wow thats the best explanation i have ,ever seen on you tube. Butifully,spoken,very clear and methodical.keep up the superb work. Thanku steve from the uk.

[@jimc6481]

Simply excellent, indispensable in tuning your engine, it's beyond guessing. Thx!

[@fogliner]

Excellent video!! Great explanation of how to diagnose problems using a vacuum guage.

[@StefanKrunic]

There's a problem with the audio! This content is too good to be lost !!!!

[@dsjkak1]

That's a great video. I like your real life analogy. I always try to come up with one when studying it this way I have an image for the theory. I always use traffic jams and exit ramps in electrical explanations .

[@dreamingcode]

Love this channel's content.

[@chrismadeley1576]

Great simple explanation ! 👍

[@RampartPh]

very clear explanation. kudos to you, sir!

[@cabin_ot]

my left ear loved this video

Great explanation!

[@paulmurphy2991]

Fabulous video, I learned so much, thank you.

[@spelunkerd]

7 months and no videos from my friend at Moss Motors. These are a great set of videos and I want you to know that you've built a fan base that needs feeding (grin).

[@eduardoarevalo4643]

Excellent video!!!

[@reazmohammed9686]

Real good advice, thanks

[@zhivago1955]

Enjoyed your tutorial, THX!

[@steveharrison4464]

your explanation is fantastic. as a layman...i thank you

[@xvrays]

Splendid tuition,

[@YungJuiceman23]

Thanks for the info. I have a 1992 Talon TSI AWD. ALl this applies to my car as well. Keep up the good work. I subscribed and liked.

[@richardengland7077]

Good stuff! I'm going to check out your other videos.

[@Subfightr]

Wow. That was informative and beautiful

[@joliemome1]

I bought my 1967 MGB new and installed a under the dash vacuum gage for fuel economy! Now for the first time I understand what the gage and engine of my car is telling me. This video was excellent!

[@charlesdowns1691]

they are good to have+i put one on my grand prix. now with a long vacume hose+reading can and should be a little less but still good. and heater blower may drop the numbers just a touch. but i check mine alot. i added.a glass pack on car and it brought vacume up a touch+and power went up too. but loud inside car a little. 18" is the preferred #. every 1000 ft above sea level vacume will go down 1")

[@charlesdowns1691]

18" steady needle at idle= normal engine.

[@chrisw5303]

Great instructions, thanks

[@pcosta9117]

awesome explanation!

[@BIGWILLY8313]

Very good explanation nice video. . Thanks

[@Atetus94]

Super informative, thank You :)

[@quicksilver6581]

Nice vid dude, thanks.

[@ghostranger96]

very neat and interesting, thanks!

[@carslover3509]

great great great explain thanks man

[@Grater812]

Very interesting! Thanks!

[@metalxesp]

awesome video thanks

[@southstar87]

Super helpful video

[@pollywogstew316]

great vids!!!!

[@grannylow7073]

Great job

[@BernieRamone351]

great video, now iam empowered with my new vacuum gauge i can diagnose my old Ford :)

[@serchmarc]

you sir are the master ,thkx

[@MrRubber81black]

great video, any chance you could do a hands on test? maybe demonstrate each scenario. Burnt valves, vacuum leak, worn rings etc?

[@miltonscornertobylove5068]

I have a vacuum gauge all this 20 plus years n didnt even know how to use til right now. Thanks 🙏 for a very well explanation!

[@chongsun8171]

awesome video. like it

[@garfic]

hi body, great video, one question, if i have a comp camp installed? can cause a variation reading in vaccum gauce?

[@SE45CX]

Thank you sir for this lesson. I've ordered a vacuum gauge from Aliexpress along with several brass fittings for connections to 6mm and 8mm vacuum hoses to do a test on my car. I do have a car equipped with Bosch monopoint injection Mono-Jetronic A2.2. Do you know if this will affect the typical manifold vacuum of 19 inHg? What would be a healthy vacuum for my car?

[@Mladen_Hadzija]

Best video I have ever sean about car mechanics, great job! Realy great video. If I understand, I can put that vacuum gauge wherever on the intake manifold of my car? My car is brand new hyundai i20, and it has injection system, but it doesn't matter is it injection system or carburator, isn't it?

[@PrasadGardenZone]

very informative

[@boobatooba1]

i. understand vacuum... thank you sooo much.

[@426gtsr]

SMART MAN THANKS!!!

[@toddler273]

thank you!!!

[@catgolfer1]

Great video! I have a Winnebago that sits on a Chevrolet P30 chassis with a 7.4L 454 V8. On the thermostat housing there are four nipples where vaccuum lines 'dead end' into. These are ported lines. There is a copper plug in the thermostat housing that takes its cue from the coolant temp. How does the temperature of the coolant activate the vaccuum. One of the lines goes to the EGR valve and is not pulling any vacuum to the EGR. David 🐈

[@Mladen_Hadzija]

Ok. I found one rubber vacuum hose located on the intake duct between the air filter and air flow meter. Other end of that hose is located on the cylinder head. Is that hose correct for mounting plastic "T" and vacuum gauge on it?

[@YungJuiceman23]

@Jafromobile Thanks for liking this and showing your subs Jafro. Much appreciated

[@mtrltoolman]

you mentioned the map sensor . what about maf sensor is it the same ? can we know if there a vacuum problem in modern cars by reading the map or maf sensors feedings ?

[@INTERNA9]

AWESOME

[@cyborgdale]

Great video. However modern cars usually has either a MAP or a MAF sensor and a select few may have both. The computer uses these sensors to determine engine load. A vacuum is still a very useful tool even on today's engines. However vacuum leaks are best determined by using an EVAP smoke machine. A Leak Down Tester can tell you a lot too. KZbin has videos on how to make your own EVAP smoke generator and how to use a Leak Down Tester. Harbor Freight has low cost vacuum gauges and Leak Down.

[@FelipeMartinez-gu5xx]

My dodge stays high above 25 at idle and i get a P0300 random misfire code. What could it be. Restricted intake? Do u think a bad Throttle body position sensor would cause that.

[@srercrcr]

I think so, where do I put the hose?

[@dsjkak1]

Also if a vacuum leak is suspected I spray lines with brake clean. Out this awesome for internal leaks.

[@MrPSNdaz1182]

Thank you.mine has been idling at 5 since I fitted it.i always believed its my carb to manifold having a leak.will get a new gasket.thanks a lot for this video very helpfull.

[@Milo30066]

Thanks

[@mydecember1985]

Could that one-cylinder rhythmic issue be a ring? I have 178-190 across all cylinders. Most 182-186. The 178 cylinder has a leakdown issue of some kind, but extremely difficult to determine the source. About 3/4" fluctuation 5 times per second or so

[@shoulderthelion-film9895]

What if your needle oscillates around 17.5 to 18.5 inHg?]

[@joshuastang6359]

Now what kind of effect does Boost have? Because when my supercharger kicks in I'm pushing pressure not vacuum

[@johnkapel2128]

Is there any way to use a Peter pump is a vacuum gauge?

[@cyborgdale]

I'm adding to my comment of just a moment ago. Leak Down Testers can pinpoint more problems but takes more time to use and you must have a compressed air source. Videos on how to use one are here on KZbin. EVAP smoke machines are too expensive to buy--make one. Get a cheap vacuum gauge and a cheap Leak Down Tester from Harbor Freight to complete your set of diagnostic tools.

[@VintageSG]

Approx 6:40 in says why vacuum gauges still have a place. You can see things like sticking/closed up valves as fluctuations in the column ( mine are manometer ). With a bit of work and thought, a set of gauges still has a place as they don't get confused by broken or cracked wiring. No bloody obscure fault codes!. If you have a motorcycle, or car with multiple throttle bodies, a vacuum gauge is the best way to balance the carbs/throttles after a service.

[@charlesdowns1691]

i usually run 18" but sometimes hangs down 1"- 2"so im reading it can be a weak ignition coil. but car runs good.

[@abimariavargas7086]

What causes cranking vacuum to rise and fall

[@srercrcr]

I dont understans why a hose would go to the head. What you can do is slide one end off, preferably the intake duct end, and put your finger on the end. Do you feel it sucking on your finger? If there's always vacuum its a good one to use. Some vacuum lines only activate once the engine has warmed up.

[@fernandomartinez5812]

AOL in the background! Or a fax machine

[@srercrcr]

I find that the 70s and 80s vehicles have SOOOO many vacuum lines that they are a prime source for vacuum leaks.

[@davidtoddmickens5558]

#$ck yeah , THANK YOU SO VERY VERY MUCH ..i have a 62 f100 - 302 ..i do not know any OG's to help me .

[@et76039]

What happened to the audio?

[@seacopotan]

Please , the sound is totally missing , fix this please , last comment was from a week ago , I think it is defective only lately then

[@edmayhew]

mmmkaaaaay

[@Mladen_Hadzija]

Sory, I understand now, it is not correct hose. Hose must be after throttle body (between throttle body and intake manifold). I found one like that, but it is very difficult to reach it :-) Thanks a lot!

[@srercrcr]

look for a spot where there may be a capped-off vacuum port (with a rubber cap). Otherwise you can purchase a pkg of T's that you can share a vacuum line with.

[@arthurmoore1524]

Analog > digital tuning. Digital has a bandwidth. Analog is unlimited.

[@ZoDDyXXX]

hahaha it´s like a puppetshow

[@kamilgezek4270]

My engine at idle was 20 inhg but at 2500 was 26 inhg and shake all car, without air filter nothing change please help.

[@naturecrunch]

did i go deaf or what happened =o i don't have sound for this video for some reason.

[@roskokov]

can be used for diesel engine

[@chriswebster1830]

росен ковачев negative, most diesel engines don't produce much vacuum if any at all

[@russcole5685]

@@chriswebster1830 correct, as diesel has no throttle body, in petrol terms, they ar always at wide open throttle

[@tonyarcos4666]

Someone get this auto technician an audio technician

[@alantownsend5468]

MAP usually stands for "Manifold ABSOLUTE Pressure" Good vid though

[@FLBill]

good video with good information, but your voice is putting me to sleep......lol

[@srercrcr]

no difference

[@elaria2007]

the sound you while u stop talking is annoying me dude

[@martiwoodchip4518]

Dude you should really stick to telling childrens stories in pre-school because with all that hand movement and your comparisons to baby birds it is obvious that is where you belong and not in any shop working on engines of any kind!.

[@fredyellowsnow7492]

@Marti Woodchip. I agreed with that for the first couple of minutes, but thankfully he dropped that analogy.

[@stevemacbr]

- I thought the 'presenter' was using SIGN language,... because I couldn't hear any audio. !!! several videos from this channel are like that. .

[@Quetzalcoatl09]

Great video!!!