Diagnosing a Misfire Without a Scanner

Diagnosing a misfire using a vacuum gauge. Watch how a misfire reflects on the engine manifold vacuum. I got vacuum reading with the misfire present, performed a cylinder power balance test to identify non-working cylinders, then performed a compression test to determine the sealing quality of each cylinder. Watch till the end to see the vacuum readings after the misfire is fixed.
Disclaimer:
The content of this video is available for informational and educational purposes only.
I cannot guarantee against improper use or unauthorized modifications of this information. MR. DIAGNOSTECH assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. Use this information at your own risk. Any injury, damage, or loss that may result from improper use of these tools, equipment, or from the information contained in this video is the sole responsibility of the user and not MR. DIAGNOSTECH.

[@chuckvoss9344]

You are correct with running these tests without a scanner. We were running these same tests 60 years ago, long before all the electronics showed up. Knowing how the basic engine operates has become a lost art. Good job.

[@charlesdowns1691]

a vacume gadge really helped me with my car+i ran it into my car now and drive it with it connected. ive learned to read and learn alot of things with it.

[@charlesdowns1691]

very true+i still use v gadge and im pretty good with. very interesting. imo

[@Maples01]

I used a vacuum gauge to set timing and mixture screws, I'm hating new electronic injection vehicles

[@davidparker9676]

@@Maples01 The new EFI vehicles are easier to diagnose if you understand how it works. You just have to get over the learning curve and you will see it is a much simpler system because each component has one job, unlike the distributor and carburetor cars. I understand both and have learned to love the simple EFI systems. A scanner is just a tool that points you in the right direction, you still need to use your brain to do the rest. Guys that rely solely on scanners spend a lot of money on parts that didn't need changing.

[@Maples01]

@@davidparker9676 I kept my carbed classic running great over 10 years before someone totaled it, this POS has lived in the shop more than my house, no one can fix it, I'll take a carb over this junk.

[@bass2762]

Good video on diagnosing a misfire. Will definitely use this on my car when it does have any misfires since it's pretty analog and doesn't have an ECU. It's a carbureted engine too so I'll have a lot to learn about tuning carburetors.

[@sheerwillsurvival2064]

Back in the day a vacuum gauge was a must tells so much even bad valves 👍🏻

[@train4905]

Dear sir. I live in the uk. An absolutely superb video sir. Very clearly explained. Methodical.and steady. A most brilliant video. Keep up the exellent Work. This has helped me fix my car . Thankyou loads Stephen

[@nickayivor8432]

Good Evening MR DIAGNOSTECH have a great day and take care MR DIAGNOSTECH Tutorial great thank you 👏 👌 👍 From Nick Ayivor from London England UK 🇬🇧

[@PaulCTownsend]

Good solid information thank you.

[@77smore]

Dude really great video thanks so much man. Thanks For contributing to the auto mechanics community

[@nighiii]

Absolutely amazing info, thank you good sir. I believe this is going to help me figure out why my carbs won't sync on my motorcycle, so even though it's on a car, I'm very thankful to have stumbled upon your video. Great job and keep imparting wisdom onto us knowledge junkies. 👏

[@humanresource9659]

This never gets old to me

[@charlesdowns1691]

no it never does for me either. always something to learn.

[@johnthemechanic2937]

Well done, I look forward to more videos from you.

[@colin5064]

WoW very good indeed excellent explanation,you are a very good teacher thank you

[@charlesdowns1691]

very intelligent. i like learning as much as possible on this

[@harvrindrsingh]

Hi from dubai. Thanks for great information

[@DIINj27]

Very clear explanation 👌 10/10

[@fransmartono8394]

Great video. Great troubleshooting steps.

[@anthonyheak3479]

Great video! This is a 4 cylinder engine. It is possible to do a compress test like this on a V6 engine when one bank of the ignition coil and spark plugs are under the intake manifold like the 2GR-FE engine on Lexus RX 350 transverse engine?

[@Donny.C.wlWilliams]

good video!!

[@leonelarenas9622]

Very helpful information 🤘

[@AF1MIDS]

I have a 2003 DODGE CARAVAN SE V6 3.3L The minivan is giving me a P0300 code. I turned on the engine and left it idling. Connected a test light to a ground and connected a vacuum gauge to a vacuum port on the upper intake manifold. I did a cylinder drop test using the test light while removing one wire at a time from the coil pack and observing the vacuum gauge needle for movement. As i was removing one wire at a time from the coil pack using the test light the vacuum gauge needle was not moving so i can know which exact cylinder is misfiring. Do you happen to know why the vacuum gauge needle was not moving?

[@fondiego9624]

More videos please

[@billspeight8936]

My Camry 2arfe has 20" of vacuum. When I snap the throttle it stays about 20" and does not drop to zero. When I turn off the engine the vacuum stays at 20" and does not drop to zero

[@MRDIAGNOSTECH]

Check your vacuum source. You might be connected to the hose that goes to the vacuum booster. These hoses usually have a check valve that prevents the vacuum from being lost for braking power assist.

[@billspeight8936]

@@MRDIAGNOSTECH thanks for getting back. I know what your saying about the brake booster line. I tried two different lines off the intake manifold both with the same results. Any other ideas I greatly appreciate

[@Rxray5050]

Good information keep them coming good job

[@nicovan7319]

i realize I am kinda randomly asking but does anybody know of a good site to watch new tv shows online?

[@zyairenixon1498]

@Nico Van I use FlixZone. Just google for it =)

[@marcelocade8897]

@Nico Van lately I have been using FlixZone. You can find it by googling =)

[@hardboiledfrog]

This is hilarious - first time I've seen multiple accounts used for spamming youtube comments.

[@charlesdowns1691]

will a longer hose+im guessing about 5 ft+ cause a lower reading? i had to run it into my car. ive read longer would give lower readings.? but mins still around 18+

[@geoepi321975]

And if it's a single cylinder how it will be steady

[@randykubick]

Shhhweeeettt. Customer drove in with a 3 cylinder and drove out with a 4 cylinder.

[@terrencecarter27]

On your compression test portion of this video, how did you connect the power probe and where's connection.

[@MRDIAGNOSTECH]

The power probe was conneted to the starter motor "S" terminal.

[@terrencecarter27]

@@MRDIAGNOSTECH Thank you. That's what I needed to know. So the power probe acted like a push button crank starter.

[@imananiyonkuru6854]

@@terrencecarter27 the contact must be at ON positin, then the power probe serves as jump wire to the stater motor.

[@charlesdowns1691]

my vacume gadge is usually steady 18_ but drops about 1 to 2" often. i read chart says ignition issue. i think i need a new set of ignition coils. 3 pack on pontiac grand prix. does this sound right about the 1 to 2 inch vacume drop and possible needing ignition coils? i put new plugs+wires on my car in september 2021. please comment+ thank you sir.!

[@rdp2370]

Hello, what did you find out about your issue?

[@charlesdowns1691]

ive not got to test anything yet+runs great. vacume needle seems to float more with heater blowing. that may be all. im gonna do more testing asap but runs like a top for now. thank you.

[@jiayihchoo9482]

Where r u from?

[@jab376]

USA

[@davidparker9676]

Los Angeles, thanks for asking.

[@levylovits]

What about an engine that is running high vacuum. About 26 at idle

[@MRDIAGNOSTECH]

Altitude plays a big role in vacuum, @ sea level the engine will produce 17-21 inches of vacuum(in.Hg). About sea level there will be less vacuum and below sea level there will be mote vacuum at the manifold.

[@colinhenry7478]

where are you from. i need a new mechanic

[@davidparker9676]

He's the west-coast Scanner Danner.

[@GUEST-qw4te]

With the engine running you should have done, spray the intake to manifold area with water,(this rules out a gasket leak), second would be to test the injectors firing circuit, feel the injector to see if it is pulsing. Being honest, if I was to see this, and I was paying by the hour...you can bet on a verbose response. Just like a compression test should be done at the time you inspect the plugs, on all cylinders at once. Also you don't need to do a compression test, if you know how to do a flood /(wot) start test. Hold down the accel to the floor and crank the engine 4-6 revs. If at any point beyond initial crank, the engine speeds up, you have low compression on 1 or more cylinders.

[@MRDIAGNOSTECH]

A relative compression test is faster and efficient, feeling an injector pulsating doesn't mean is working, it could be clogged. This video was to demonstrate how vacuum can reflect engine driveability issues.