In this video I follow my gut on a repair and develop a test to prove my gut feeling. I'd be interested to hear your thoughts. How would you diagnose a vehicle that you suspect was loosing compression under load? -Enjoy!
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South Main Auto Repair
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Avoca, NY 14809
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Due to factors beyond the control of South Main Auto Repair, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. South Main Auto Repair assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. South Main Auto Repair recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of South Main Auto Repair, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained.
If an SMA Video has helped you out please consider giving using "Patreon" to help support us. The videos take real time to create and pull us away from real work that pays our bills. CLICK HERE: https://www.patreon.com/southmainauto
CHECK OUT OUR "SMA SWAG" STORE! Go on Teespring and get your very own SMA merch!
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If you don't like Patreon feel free to use the "PayPal Me" link: https://www.paypal.me/SouthMainAuto
The South Main Auto Amazon Store:
https://www.amazon.com/shop/southmainautorepairavoca
AES Wave Automotive Diagnostic Tools: https://www.aeswave.com/cart.php?m=affiliate_go&affiliateID=2525b91fc8e906e8215984074c9d9e8f&go=https://www.aeswave.com/Miscellaneous-p9347.html
Thank you for all the continuing support!
--Eric & Vanessa O.
Feel like sending some swag to SMA because you love the videos but don't know where to send it?
Just ship it here:
South Main Auto Repair
47 S. Main St
PO Box 471
Avoca, NY 14809
Disclaimer:
Due to factors beyond the control of South Main Auto Repair, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. South Main Auto Repair assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. South Main Auto Repair recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of South Main Auto Repair, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained.
Had Blazer 4.3. Exhaust valve
Bloody Brilliant.
That cracked windshield gives us a good idea of how well the vehicle is maintained.
I'd try seafoam first. It's quick easy and inexpensive. Roll the dice. If that didn't work, then we do it the hard way. Pull the head. I don't know why people just keep driving a defective vehicle until it won't hardly run at all anymore. Or drive a vehicle with a severely cracked windshield. She doesn't seem like the type to take good care of her vehicle nor would she want to put much $$ into it. So go with the seafoam. BTW Great diagnosis and test drive (give her full beans uphill) Good instinct too. (you knew)
Ensure crankcase has a good grade of full synthetic oil, and oil pressure is good….then , use marvel mystery oil, or similar (sea foam) to gas tank. In a pinch, 2 cups of full syn motor oil or 2 cycle oil in a tank of gas will work.
From there, I'd let her cool down, pull the #3 spark plug, & put the smoke machine to it. If smoke comes out the intake, it's the intake valve sticking. If it comes out the exhaust, it's the exhaust valve hanging up. My bet is exhaust valve, as the converters were cooked recently, & an improper seal coulda let a buncha junk poison the cats. Fun stuff! Big fan of yours too, I love this channel.
Take it to a mechanic since I am no where close to being able to diagnose such a thing. LOL
Motor Kote
probably has a Nissan Altima engine?
Man. I sure wish your shop wasn't 1000 miles away. I have 2 vehicles that need more diagnosis than any shops I know of in town are capable of, and frankly they've both been to 2 or 3 each without any progress and Im tired of wasting money
Ok.. so what happens to the lifter of the offending/sticking valve? What about its pushrod? Are we talking about the valve sticking .050" off the seat? Assumably or p to v would be an obvious issue, lol.. To your question.. i guess i would leak it down in the shop and might even pull a cover. Great vid as usual.
Do you ever work on Chevy HHR's their junk but I own one but they're easy to work on so I like mine
Thank you for this video! Another tool in my cart aka brain!
I had this same problem back in 1981 but it was on a Kohler 14hp lawnmower engine. After running for about an hour the engine would shutoff with no compression due to exhaust valve warping. Luckily I was close enough to hear the engine freewheel to a stop. Currently I have a 2000 GMC van with the 4.3L that does just the opposite. With warm engine it misses at idle and runs fine under load. I only have a single channel Pico scope so I'm not sure if I can see it on that. Might have to make a trip to SMA just to verify it.
I'm going to invent a spark plug Y harness that allows both the spark plug (still firing the cylinder as it normally does) to be installed along with an auto-bleeding compression tester that can be observed while driving.
Or maybe someone much smarter than me can do that.
I’d diagnose it by driving up to you letting you have at it.
Your way to diagnose the problem was probably about the only way, you had to catch it the act. I like your starter draw / weak cylinder diagnosing method. It sure did prove effective with this repair. Good Job!
I'd check the gear oil in the windshield washer reservoir & lube up the headlight bearings first, after that I'd check the water pressure in the tires before climbing up that big hill.
Had small block in small truck years ago started missing after climbing hill, then would smooth out found it was weak valve spring and lifters would pump up, then when back to idle would smooth back out as oil pressure dropped, took me ages to find.
What I wouldnt give to be able to work for a smart mechanic like you, not a lot of good techs in my area.
Leave the wires in place, as you drive. The wires are not big enough to present a problem with the hood.
This guy is GOOOOD! Best mechanic I've ever run across. Keep up the good work Eric O.
You pretty much nailed down the diagnostic procedures for that type of misfire. The lab scope is a great diag tool, especially if you know what your doing. Great job Mr. O.
Is Fluid Film a sponsor?
Will that car pass inspection with that windshield crack?
How i would diagnose it is bring it you .
Sorry I am late to the party just catching up with recent vids. Nah, not me, I'd be stuffed as I do not have access to the equipment or software Mr O has. Only option for me is find a bloody big hill, let it play up for as long as I can then jump out and hit the exhaust manifold with a temperature probe or laser and see if it is below the others. Either way it confirms it is not giving full power out of that cylinder. Then maybe have a look at the valve train to see if I have a lifter pumping up or a valve clearance issue? Swap out the lifters for new ones as a cheaper option?……maybe an oil cleaner flush and new oil? Then off with its head if all else fails!
I also know a guy in Avoca, but buggered if I am driving the car from Brisbane Australia to see him.
Sorry, lady. Pre-existing conditions are not covered. That's a separate job.
Had this happen on my mustang comebto find out it was a weak coil within the injector when PCM signaled more voltage it would become weak and lean out
Seems like a stuck open valve would create a rocker arm clank while the valve is stuck open. That would be a dead give away.
Watching a lot of car repair videos, I think there is a strong and direct correlation between cracked windshields and poor maintenance. If the owner is willing to drive with the whole windshield cracked, then they are likely to be lax on doing preventative maintenance. In this case, a hanging valve is probably caused by lack of adhering to proper oil change intervals…dirty oil. BTW, an awesome technique to diagnose this problem. Thanks Eric for sharing your time and knowledge.
Can Sea Foam damage a catalytic converter if put in the intake manifold to clean carbon?
SEAFOAM THAT PUPPY ……………..
Keep up the good work , new subscriber , love your videos.
Had same issue on 97 suburban 5.7 and 98 astro van 4.3 common issue , started running shell gas has extra cleaner in it , problem went away . Carbon build up on valve guide. Problem also would go away when I'd drive on a long hard trip , it would slowly get better and go away .
How would you diagnose it? Drop it off at the dump, buy a Ford. I had an Impala with the same issue
My non Vortec 4.3l in 91 S10 had valves sticking after sitting overnite, was hard to start but once warmed up was fine till cooled off, Make sure the vortec engine has a good dist cap where the wires come out on the sides, aftermarket caps bad bout misfires.
Humor and learning, great combo, not many good mechanics out there, this guy does great work.
Easy, grab the engine, throw it across the room and fixed 😂
Try a CKP relearn. I had a Vortec with vacuum leak on intake. Replaced gaskets, Tahoe ran fine. When going up hills misfires would start (CEL would flash) performed CKP relearn, no more misfires. why that fixed it I have no idea. I would need to see a compression gauge on that #3 cylinder to truly believe in pulling the head.
weak valve spring?
Looks like exhaust valve. treat with——-
I used to have the same problem with the exhaust valve on a single cylinder Kohler engine. Valve would stick open, the engine would miss, cooling off the valve, then run good again. Quick fix was to ream out the valve guide and wire brush the exhaust valve stem. It would last a few years.
Good thing people buy Chevy's in your area. Otherwise you might not have a business. You have some many Chevy videos on your channel. LOL
A relative compression test is the way to go. From your waveform I suspect it is an intake valve issue. An exhaust valve not opening has a very unique signature. Usually, I see intake valves cause a lower trough like your capture.
This was a good one to share with everyone. Don't ever feel underappreciated by the subordinate techs in the shop. I always looked up to my senior techs for their wealth of knowledge and experience.
I would just drive it the way it was until it got to the point that it would be safe.
What did the customer end up doing?
My approach would be to search your channel first to see if you've already encountered this problem. 😉