phenomenal presentation!! i used your video to diagnose a 2011 subaru forester. swapped coil, plu, checked intake for vacuum leak around that cylinder. then had a bouncing needle like in the video. did leak down test exhaust valve leaking
The good old days were when the basics made the most sense. Engines are basically air pumps, and a simply vacuum test can tell you how mechanically sound or not the engine is. Thanks for commenting.
Having been in the buisiness for 20 years (70-90s) I must tell you it amazes me to see the time you take to make these videos. I know how busy it can get and have much appreciation for your sharing of knowledgeable and time. I'm not sure if this is the proper forum but I have recently started turning wrenches again after almost 20 years out of the field. I volunteer at a great church that has a shop with 3 lifts and fixes cars for people who can't afford retail repairs. My question is, if we were going to invest in a scanner/scope which would you recommend? Again, thank you very much!
The best would be the Manufacturer specific OEM software that runs on the laptop with a usb to OBD dongle. But thats impractical and costly. Other than that, there is no best 3rd party obd scan tool. What one scantool doesn't do well in, the other one can and vice versa. If you had to pick the least suckiest, i would say its between the Snapon Verus Pro and Autel maxisys ds908.
As usual, an excellent video. Thanks so much for taking the time to make them. Your videos have helped me on several occasions to go past my usual comment of "Now what do I do," to actually finding the problem and fixing it.
Great demonstration with the engine minus valve cover. I was curious about whether a leaky exhaust valve would have the same magnitude fluctuation on the vacuum gauge as a leaky intake valve.... it looks like that is indeed the case. This video is still helping people out 10 years later.
Excellent video Duane! The guys in the field forget about this test all the time. Once it is understood, it is easy to perform and is extremely accurate. Nice work my friend! Mark Hicks Wells Vehicle Electronics
Good video. However, I found myself caught out with a modern engine with advanced "direct injection". Turns out that this type of engine doesn't generate a vacuum when cold starting. Instead, it opens the throttle quite wide, and changes the valve timing and injector spray pattern/timing, so that "deactivate" most of the engine's displacement. Once the engine warms up for 30 seconds, then the ECU switches to "normal" idle control with closed throttle and big vacuum.
Very helpful on my old chevy ,thanks .By the way ,you may want to ask your other mechanic to make background noise elswhere while filming, kinda distracting ,just saying
Good video but for dummies (like me) shall be a little more detailed ... Hooking the vacuum gauge "below the throttle plate" does not tell me anything. I need to see the exact location where the vacuum gauge is connected. Other than that it is one of he best explanations I've could find on YT regarding the entire process... I've spent numerous hours to find a clear explanation, where I could connect to vacuum gauge to check a 5.8l, 351W engine. All I could find was "the intake manifold vacuum"...Nobody has made a video to specifically show the location. Not even the books I have about the 351W show that. Thanks for posting!
Question: What is causing my carburetor to run the best and perform the best at a very very lean position on the accelerator pump lever and very lean on my air fuel mixture screws? I just wanna raise hell and do it for Dale but it dosent have enough reaponse OR " TTHWACKK!" As I would like for it to/know it should have. Its A 1972 010 SBC 350 Its a 600cfm edelbrock carburetor, Toker II intake, A slightly larger cam lift and duration than stock, nothing radical, I wouldn't even call it mild . Headers w/y pipe to catback muffler. And the previous owner sniped off the detent/kickdowm cable going from the th350 Trans. It shifts at good points still, seems to hold gears and downshift as it should. Vaccum routing currently in my tune where it runs best: •PCV to front of carburetor., center big.port •vacuum advance is hooked to ported side of carburetor. •I have a vacuum Guage hooked up inside my car for tuning, and it's more less plugging the manifold side because it's the only thing hooked to it. • Brake Booster and Modulator Valve are both hooked to intake stand, as GM/CHEVROLET calls for a engine of this Age (1972 w/no emissions control) It dosent run hot, no detonation, I thought it had a lifter pecking but after all day with a timing light advancing and retiming, it's gone. It was very late, now it's on the money. I'm 99% sure my initial timing is 34 degrees. It cracks right off when you turn the key. I'm also getting a very very very very faint movement in tbe needle on my vaccum Guage. It moves with the "lump" of tbe cars idle. I don't think it's that big of a deal. It dosent backfire or pop running or accelerating or slowing down. It dosent idle badly, About 1k in park, 650 in drive. Its got me stumped, I'm usually never stumped but lord have mercy she's got more power then this surely to God. It had more power with the distributor as retarded as a special needs clown. Now it's in time, getting plenty of fuel on the very lean carburetor setting even, plenty of spark. I need help from my peers of youtube pls I refuse to get walked on by 4cyls. I will make power or I will make a rod knock on heavens door trying I have spare engines refurbished, bagged, and standed. I just wanted to make this specific one perform "I wanna go fast" -Ricky Bobby
one quick question ive always had is these days finding ways to hook up my vacuum guage seems to be getting harder and harder and i still like to use the guage as a diagnostic tool
Its interesting that the vacuum gauge was much more erratic when there is a problem on the intake side than on the exhaust side. In your test, it looked like the vacuum gauge needle mimics the frequency of the exhaust valve. But on the intake side, the vacuum gauge jumped at maybe twice the rate of the frequency of the intake valve. Is there a correlation or is this just a coincidence?
what should my vacuum gauge read with a camshaft thats alittle bigger than your stock cam ..i have a 1990 k5 blazer 350 engine it has rebuild with up graded the cam to a howard rattler cam intake lift 225 exhaust 535 duration 227/235 lobe separation 109 centerline 103 i check to see how mush vacuum i were getting and its no where near 19 to 21 of mercury .. the needle is in the red area sitting on 10 where it say late value timing or leak at intake manifold or heat riser my engine has about 480 miles on it
One other question, if I have done a scope relative compression test and I can clearly see that two of my cylinders are lower than the others, is there any real need to do an actual gauge compression test?
I have 2012 Subaru forester with rough idle problem. change spark plugs, fuel pump and O2 sensor with no success. can this test diagnose the problem? thanks in advance
Wow, this is really good information. Question, is the vacuum in the correct range and the needle not shaking definitive evidence that the engine does not have compression problems? Or is it only definitive that you don't have leaking valves?
Great question. The second is true because the vacuum is created when the valves are closed and the intake pistons moved down. Compression is created when both valves are closed and the pistons move up. For that, you need a compression gauge. Good results on both tests would confirm goog vacuum and good compression equals a good mechanical engine.
D, If u have a vehicle with no( service engine light) on and no noticeable problem such as misfires etc. Would this vehicle or such type vhecals make good practice for hooking a scantool , to recognize good data value such as o2 values, fuel trim, etc??
Hi I have 1990 c4 corvette fitted with a high lift cam which is burning oil i have been told it is the valve stem oil seals i have done a vacuum test and it is reading a 15 mg the needle moves back and fourth very slightly also been told this in normal with a high lift cam is this correct or should a be worried
We always just did a compression test but I guess this is the new way. Just had a shop say my sisters car 93 Camry has burnt or thinning valves because of a fluttering needle on the vacuum test. He would not do a compression test, he said it was a waste of time. What do you think?
A compression test would not be a "waste" of time, it would simply confirm and/or be more evidence of what is highly likely. A compression test takes time, so it costs you money. If your tech is considering the fluttering needle along with other evidence he has gathered, he is saving you money by not doing the test. However, a fluttering needle as the only evidence would not be enough evidence to condemn the engine. Several things can cause a needle to flutter. Ask him to explain it in more detail.
is it common for a cheap vacuum gauge to not work,, when im looking for 30in mine reads 5, seems so far off, im gonna get a 2nd one and test em against one another
I just had break lines put on my ford Taurus. running perfect prior. as im driving home its idle and timing all off,, as I break it wants to staul and as I gas it revs up waay to much. any ideas, did they touch my idle and timing to fix the break lines or they mabey accidently knock something loose?? help?
I am sitting steady at 21 inches of vacuum at idle. I get these shakes at idle that I thought were misfires. However this gauge does not move at all. Should I rule out misfires because the vacuum is steady and move on to engine mounts or harmonic balancer? Would an engine with one bad cylinder show up as a jump vacuum gauge at idle? Because the bad cylinder would draw less vacuum at the moment that it is on the intake stroke?
A steady vacuum needle is a very reliable sign that the problem is NOT internal to the engine. Keep in mind that vacuum is created by properly sealing and proper mechanical movement. Misfires are created by ignition (spark or fuel ) disturbances. I would definitely verify your mounts and balancer are good. If so an ignition scope would be my next step
@@realfixesrealfast ru-vid.comNChSlYceEsE?feature=share I took a video of my balancer and it does appear to move in and out a little bit. I also noticed dry rotting/cracking in the rubber of the balancer as well as one of the mounts. I thank you for your time and your EXCELLENT information that you provide. You have helped me really understand so much and you have helped many others.
@@realfixesrealfast is it safe to assume that if vacuum holds really steady at idle that I don't have any power balance issues that would show up on a relative compression test? If any cylinders are producing much lower compression and there was a power balance issue wouldn't that show up on the vacuum gauge as a fluctuating needle?
I didn't know you did any sort of teaching outside of these RU-vid videos. Only thing I gotta add to this is if you're gonna do any of these tests, get a GOOD vacuum gauge, not one of those el-cheapo vacuum pump gauges like you get from AutoZone. The needles on those have a lot of bounce even on a perfectly sealing engine.
I don’t suppose this test can be done with a diesel? Or can it cause I’ve done work an graduate college for automotive but I have never seen this done. It’s not even mentioned
@@realfixesrealfast thank you sir very much for replying I’ve saved lots of your videos when I was younger studying gasoline. An I’m still learning from you. God bless you sir. If you come across a video of the procedure an understanding of a return flow test for the Cummins injectors an the Duramax injectors please let me know. I would love to see how there done for diagnosis reference.
First, thank you for this excellent video! Second, my recently rebuilt engine has a fairly intense vibration at low rpm. My vacuum gauge is also vibrating back and forth between about 19-21 in Hg at idle. Could these things be related?
on multiple older carbureted motors and efi engines. One of which is a fresh remanufactured motor that runs great, the vacuum needle on my gauge always shakes back and forth a bit on every one. Engine doesn't burn oil or anything. I've never seen a vacuum gauge needle be completely still like I see in these videos. Is this necessarily a problem?
The response of the needle on any vacuum gauge is purely a physical law. The needle moves in response to changes in pressure upon it. I have seen perfectly steady needles on engines all the time. So, if your needle is NOT steady you either have a bad gauge or one of the many factors that can affect vacuum is occurring. You said you engine is "a fresh remanufactured motor that runs great". "Engine doesn't burn oil or anything". Ok that's fine but the science still holds true. Keep this in mind, that fresh, runs great, non oil burning engine may be out of base timing just enough to cause the needle to be unsteady. There is an underlying cause. You just need to find it.
@felipevinalay For an injector balance test look at ScannerDanner's channel, video "2003 Pontiac Vibe 1.8L Misfire, Rough Idle". It is a two part video. He uses a fuel gage and OTC Fuel Injection Pulse Tester part # 3398. Be sure to subscribe to these channels. That's how they finally make YT partner and get some money for their hard work.
