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Embarrassing low dyno numbers and need some help

This is a discussion on Embarrassing low dyno numbers and need some help within the General Help forums, part of the LSx Technical Help Section category; Last night when i pulled the plugs i tested the #8 using the plug. Turned the light off in my ...

  1. #21
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    Last night when i pulled the plugs i tested the #8 using the plug. Turned the light off in my garage and verified spark. Also used my infrared temp gauge to verify the #8 header tube was heating up when the car was running. I have also read that a weak battery or starter could be causing the issue. I had the battery twsted a few weeks ago and it was a little low on charge but tested good.

  2. #22
    Spaz is My Mentor SMWS6TA's Avatar
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    hey sorry miss read and typed the above post so I paste in what the manual states so you can read it.

    All cyl are below 100 psi but are within each other in percentage and #8 is not warming up


    I think at this point I would check the harness and injector still. You've found a challenge here. This is not making any sense.
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  3. #23
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    This is what i found per the service manual

    Cylinder compression on LS1

    From the service manual:

    Engine Compression Test

    Charge the battery if the battery is not fully charged.
    Disable the ignition system.
    Disable the fuel injection system.
    Remove all the spark plugs.
    Block the throttle plate wide open.
    Start with the compression gage at zero, and crank the engine through 4 compression strokes, 4 puffs.
    Make the compression check for each cylinder. Record the reading.
    If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole.
    Recheck the compression and record the reading.
    The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1035 x 70% = 725) (150 x 70% = 105).
    Normal -- Compression builds up quickly and evenly to the specified compression for each cylinder.
    Piston Rings Leaking -- Compression is low on the first stroke. Compression then builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
    Valves Leaking -- Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.
    If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the cylinders.

    From what I have been reading on the forums most people have numbers in the 170+ range

  4. #24
    Spaz is My Mentor SMWS6TA's Avatar
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    Try squirting a bit of oil in the cyl and repeat the test.


    This will check to see if it's the rings.

  5. #25
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    I will have to try it when I get home. I really hope its not rings or a rebuild is in my future

  6. #26
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    Ok so update. I spent the weekend working on the car and found the issue. The timing was off by about 1 1/2 teeth. Once I set the timing the idle smoothed out and the car doesn't feel sluggish. It os much more responsive and feels like it picked up a bunch of power. I checked the compression again and all the cylinders were above 180psi. So with the timing off the valves must have been open a littlw and that was causing the low numbers

  7. #27
    Senior Member Naaman's Avatar
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    Damn... isn't it awesome how shops and dealers can't find things with all their computers and gizmos and what not... but some time in the garage with some music and drinks makes things new again?
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  8. #28
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    Yes it is lol. My back is killing me but it is worth it to finally have this thing running right. Beer and music helped things go smooth. I will have to take it back to have it tunned again because the idle is a little high but the shop is going to do the retune for free. Im interested to see the numbers it makes.

  9. #29
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    So glad you found it.

    What made you decided to go back and check the timing chain/gear?

  10. #30
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    Well after I did the compression check and found all the cylinders low I had a friend do a leak down test and we found all of the valves were leaking. So we figured the timing must be off or there was a serious head issue. I wish I could upload a photo to show you all how far off timing was

  11. #31
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    I'm going to try to remember this if it ever comes up again. Glad you posted what you found. Not a common occurrence.

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  13. #33
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    I always try to post up what solved my issues so other can try if they run into the same thing. I attached a picture so you could see how far off the timing was

  14. #34
    Spaz is My Mentor SMWS6TA's Avatar
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    that wasn't a few degrees....You were in the tens of degrees. You lucky you have it stock length piston rods, otherwise you'd would have had serious PTV issues. I'm amazed it started at all.

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    Thats what everyone has said. The tunner didn't believe me until i showed him the photo

  16. #36
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    So found a small oil leak. The leak is where the lower bolt connects the oil pan to the timing cover under the car. About a inch long hair line crack. I bought permatex spray n seal and this stuff works. Its like a clear rubberized coating. You clean the area and spray 5 coats on. It seeps into the crack and seals it. Only works on non high pressure areas.

  17. #37
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    Did you remember to put some rtv in the corners where the front cover, gasket for the oil pan meet?

    Also to align the cover properly you leave the front cover bolts a little loose, enough to still hold in place but loose enough to slid it with a little effort. Next tighten the oil pan to the block and then the bottom 2 bolts to the cover. Now tighten the front cover bolts. I've yet to have a leak issue doing this way.

  18. #38
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    Yea I put the RTV in the corners. I also used the tool to align the cover properly. I think when I tightened the bottom bolt i over tighten it a little. Im planning on dropping a new motor in nevt year so its fine. The crack is very small and not worth pulling the pan. Ill jist monitor it and make sure its fine. The only issue i am having now is the fuel economy sucks. And i rairly drive the car hard. At the moment im getting 10.5mpg city. My daily commute is all highway at 70mph. I use the cruise control.

  19. #39
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    Didn't you get it "tuned" while the timing was out? If so that is the issue.

  20. #40
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    Yea i did. Im supposed to go in today hopefully for a retune

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