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Thread: Compression test on EL

  1. #1
    Sir Car Reviews Franco Cozzo's Avatar
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    Compression test on EL

    Hey guys, just wondering if anyone here can give me a run through on how to properly do a compression test on an engine.

    I'm suspecting toasted rings on my EL Fairmont Ghia, which might be the reason it feels so torqueless, but it is making 138KW at the rears.

    I've got a compression gauge, last time I tried the test I drove the car for about 100km, then pulled all the plugs and tested all the cylinders with no plugs in but I've been informed this is incorrect? I kept cranking it until it wouldn't go any higher on the gauge.

    What is the correct method?

    Thanks much.

  2. #2
    Jacob
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    I know of two methods. What you've done, a dry test. And also putting a small amount of oil in the chambers, a wet test.

    A higher reading with the wet test over a dry test I've been told should pinpoint piston ring wear.
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  3. #3
    Ich bin ein auslander! Lynton's Avatar
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    Correct.

    A dry test will identify the cyinder that is down on compression but this may be de to ring/bore wear, broken head gasket or valve wear.

    A wet test will further diagnose. No change in the wet test compared to the dry will show either a damaged valve or head gasket. An improvement compared to the dry will show it is damaged ring/bore.

    What engine is it that you are asking about? Is it blowing smoke or consuming oil? Is there any water in the oil or oil in the coolant?
    Growing old is compulsory, growing up is optional!


  4. #4
    Sir Car Reviews Franco Cozzo's Avatar
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    EL Fairmont Ghia, Tickford head with bigger exhaust valves, cam, shaved and ported/polished.

    Missfire on one of the cylinders at idle, and I've replaced all the ignition system components minus distributor, new AU Falcon MLS head gasket.

    Doesn't blow smoke or use oil, just seems to lack torque.

    Was dyno tuned with a J3, put out 138KW at the rears.

    How can you tell if the auto is slipping? It doesn't rev out while driving but it feels like it has absolutely no balls, and it needs to kick down gears all the time to maintain speed on any sort of hill, couldn't even spin the wheels if you tried unless it was wet.

  5. #5
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    Quote Originally Posted by Big Damo View Post
    EL Fairmont Ghia, Tickford head with bigger exhaust valves, cam, shaved and ported/polished.

    Missfire on one of the cylinders at idle, and I've replaced all the ignition system components minus distributor, new AU Falcon MLS head gasket.

    Doesn't blow smoke or use oil, just seems to lack torque.

    Was dyno tuned with a J3, put out 138KW at the rears.

    How can you tell if the auto is slipping? It doesn't rev out while driving but it feels like it has absolutely no balls, and it needs to kick down gears all the time to maintain speed on any sort of hill, couldn't even spin the wheels if you tried unless it was wet.
    Great reply Lynton, 100% correct, normally a slipping transmission torque convertor would result in slightly higher engine temperatures.
    This is of course dependant on you running the original oil cooler in the radiator.
    Another old time trick is to inspect the color of the transmission oil & the smell of the oil, if it is off color or smells burnt, you will have found the problem.
    Another old time method, was to monitor road speed as against engine revs, more engine revs to maintain engine speed would indicate a slipping clutch.
    Hope this helps & good luck with your diagnosis.

  6. #6
    Sir Car Reviews Franco Cozzo's Avatar
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    The trans was overheated a few times by the previous owner, so wouldn't surprise me if its cooked, I've got a T5 here anyway ready to go in.

    I did the oil and filter kit through the trans before I registered it and it was real dark.

  7. #7
    Ich bin ein auslander! Lynton's Avatar
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    Quote Originally Posted by Big Damo View Post
    The trans was overheated a few times by the previous owner, so wouldn't surprise me if its cooked, I've got a T5 here anyway ready to go in.

    I did the oil and filter kit through the trans before I registered it and it was real dark.
    Does the auto change ok? Is there a delay in the shift, slipping or clunking?

    Is the car behaving like it is lacking power (as in bogging down and slow to accelerate) or is it revving out and slow to accelerate?
    Growing old is compulsory, growing up is optional!


  8. #8
    Sir Car Reviews Franco Cozzo's Avatar
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    Bogging down and slow to accelerate, won't spin the wheels either unless you are on wet grass.

  9. #9
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    Quote Originally Posted by Big Damo View Post
    The trans was overheated a few times by the previous owner, so wouldn't surprise me if its cooked, I've got a T5 here anyway ready to go in.

    I did the oil and filter kit through the trans before I registered it and it was real dark.
    I think you have nailed your problem.
    3 pedals & a gearshift are a lot more fun!!!!

  10. The Following User Says Thank You to project 064 For This Useful Post:

    Franco Cozzo (26th September 2013)

  11. #10
    Sir Car Reviews Franco Cozzo's Avatar
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    Tell me about it, got two manual cars and two autos, the autos are crap, both 4sp, one BTR93 and a 4L80E from Government Motors.

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