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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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49 thoughts on “How would you diagnose this one!?”
  1. Avataaar/Circle Created with python_avatars mitch lrp says:

    Had Blazer 4.3. Exhaust valve

  2. Avataaar/Circle Created with python_avatars Otto Teller says:

    Bloody Brilliant.

  3. Avataaar/Circle Created with python_avatars Andy Bonneau says:

    That cracked windshield gives us a good idea of how well the vehicle is maintained.

  4. Avataaar/Circle Created with python_avatars David Timmel says:

    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)

  5. Avataaar/Circle Created with python_avatars Tom Sawyer says:

    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.

  6. Avataaar/Circle Created with python_avatars Andrew Edwards says:

    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.

  7. Avataaar/Circle Created with python_avatars covishen says:

    Take it to a mechanic since I am no where close to being able to diagnose such a thing. LOL

  8. Avataaar/Circle Created with python_avatars Mr D says:

    Motor Kote

  9. Avataaar/Circle Created with python_avatars SilverBullet93GT says:

    probably has a Nissan Altima engine?

  10. Avataaar/Circle Created with python_avatars AngryDINGUS says:

    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

  11. Avataaar/Circle Created with python_avatars Ron Spencer says:

    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.

  12. Avataaar/Circle Created with python_avatars Ron Murray says:

    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

  13. Avataaar/Circle Created with python_avatars Nathan Higgins says:

    Thank you for this video! Another tool in my cart aka brain!

  14. Avataaar/Circle Created with python_avatars The Admiral says:

    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.

  15. Avataaar/Circle Created with python_avatars Jerrell Strawn says:

    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.

  16. Avataaar/Circle Created with python_avatars Scott Berge says:

    Iโ€™d diagnose it by driving up to you letting you have at it.

  17. Avataaar/Circle Created with python_avatars Doug Kubash says:

    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!

  18. Avataaar/Circle Created with python_avatars Robboned says:

    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.

  19. Avataaar/Circle Created with python_avatars Peter Levy says:

    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.

  20. Avataaar/Circle Created with python_avatars Mrdubomb says:

    What I wouldnt give to be able to work for a smart mechanic like you, not a lot of good techs in my area.

  21. Avataaar/Circle Created with python_avatars Michael Knorr says:

    Leave the wires in place, as you drive. The wires are not big enough to present a problem with the hood.

  22. Avataaar/Circle Created with python_avatars Chip Haverstick says:

    This guy is GOOOOD! Best mechanic I've ever run across. Keep up the good work Eric O.

  23. Avataaar/Circle Created with python_avatars EARL WITHERALL says:

    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.

  24. Avataaar/Circle Created with python_avatars Terry324 says:

    Is Fluid Film a sponsor?

  25. Avataaar/Circle Created with python_avatars Terry324 says:

    Will that car pass inspection with that windshield crack?

  26. Avataaar/Circle Created with python_avatars Jared THISDELLE says:

    How i would diagnose it is bring it you .

  27. Avataaar/Circle Created with python_avatars Mice InOz says:

    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.

  28. Avataaar/Circle Created with python_avatars HunterShows says:

    Sorry, lady. Pre-existing conditions are not covered. That's a separate job.

  29. Avataaar/Circle Created with python_avatars sederick coxson says:

    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

  30. Avataaar/Circle Created with python_avatars Robert Britton says:

    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.

  31. Avataaar/Circle Created with python_avatars Frank D says:

    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.

  32. Avataaar/Circle Created with python_avatars Manuel Flores Sr. says:

    Can Sea Foam damage a catalytic converter if put in the intake manifold to clean carbon?

  33. Avataaar/Circle Created with python_avatars jhack says:

    SEAFOAM THAT PUPPY ……………..

  34. Avataaar/Circle Created with python_avatars Peter Ravensbergen says:

    Keep up the good work , new subscriber , love your videos.

  35. Avataaar/Circle Created with python_avatars Peter Ravensbergen says:

    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 .

  36. Avataaar/Circle Created with python_avatars David Southwell says:

    How would you diagnose it? Drop it off at the dump, buy a Ford. I had an Impala with the same issue

  37. Avataaar/Circle Created with python_avatars jocrp6 says:

    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.

  38. Avataaar/Circle Created with python_avatars Mike Alexander says:

    Humor and learning, great combo, not many good mechanics out there, this guy does great work.

  39. Avataaar/Circle Created with python_avatars lucianoromero777 says:

    Easy, grab the engine, throw it across the room and fixed ๐Ÿ˜‚

  40. Avataaar/Circle Created with python_avatars Matt Roberg says:

    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.

  41. Avataaar/Circle Created with python_avatars Andy King says:

    weak valve spring?