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when you check the compression. do you need to....

Discussion in 'Engine Building' started by The WORLD is yours..., Sep 25, 2004.

  1. The WORLD is yours...

    The WORLD is yours... Senior Member

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    i've been told by a trust'd friend that i need to have the gas pedal floor'd to have an acurate compression reading!?!
    but.....

    i've read nothing of the sort!!!

    any imput?

    thanks
     
  2. jamesA

    jamesA Well known pissed off telephone guy VIP

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    When I was taught to do compression checks you should never turn the motor on, just let it crank over but not start two or three times for each cylinder.

    ;)
     
  3. The WORLD is yours...

    The WORLD is yours... Senior Member

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    right i have the dizzy plugs un-plugged.

    he said something about it "letting air to the cylinder's" so i can get an accurate reading!!?!!

    thanks
     
  4. jamesA

    jamesA Well known pissed off telephone guy VIP

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    just pull the plug of the cyl you're working on, plug in the reader, crank it over a few times and move on to the next one.
     
  5. The WORLD is yours...

    The WORLD is yours... Senior Member

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    how i do it is:
    like the directions says!

    un-plug the dizzy. take all the plug wires off. and take all the spark plugs out. then put the tester in each cylinder, and crank the engine over until the compression gauge needle stops!!
     
  6. jamesA

    jamesA Well known pissed off telephone guy VIP

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    pretty much. thats exactly how i was taught to do it.
     
  7. The WORLD is yours...

    The WORLD is yours... Senior Member

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    k, cool!!

    i just want to see if anyone else does it the way my friend does it!!
     
  8. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    yes you have to put your foot on the gas pedal. if you dont you will get extremely low readings. unplug dizzy, unplug injectors and just crank. let it go like 6-7 rotations and get your reading. you MUST have your foot on the gas pedal or something holding the throttle open to get the right readings.
     
  9. The WORLD is yours...

    The WORLD is yours... Senior Member

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    k now i have 1 for "no" and 1 for "yes"!!

    anyone else?
     
  10. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    its YES, believe me, ive done it. i forgot to hold the gas pedal down at first and got readings like 90/60/60/90, in reality when i didi it the right way i got 215/210/210/215
     
  11. beerbongskickass

    beerbongskickass Senior Member

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    Yes you need to hold the gas all the way to the floor while your cranking the motor over. Make sure the car is at operating temp also, I take the ECU fuse out so I won't get fuel, then I just take out one spark plug and screw the compression tester in. Hold the gas to the floor and crank it over 5-10 times (until it stops going up), then do the same for the other plugs.

    http://www.c-speedracing.com/howto/comptest/comptest.php
     
  12. jamesA

    jamesA Well known pissed off telephone guy VIP

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    Maybe my shop teacher had a different way of doing it. I dunno. fine, hold the gas pedal down. :shrug:
     
  13. beerbongskickass

    beerbongskickass Senior Member

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    The first time I did a compression test, I did it without holding the gas down, then I did it while holding the gas down, the numbers were higher while holding the gas down. I have also did a compression test while my engine is cold, then while the engine was hot and the numbers are much higher when hot.
     
  14. deejay

    deejay Junior Member

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    have your throttle wide open
     
  15. The WORLD is yours...

    The WORLD is yours... Senior Member

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    sweet!! thanks for the help!!

    well i did the compression test without holding the gas pedal to the floor and got: 260,260,260,260 a few months ago!!

    well i did it again yesterday and i got(without holding the gas pedal to the floor): 262,245,115,240

    on monday i'll do it again. but with the gas pedal to the floor!! see what i get then!!!

    thanks again

    oh i forgot to add. when i did the compression test yesterday. on the 4th cyl. while performing the test. i heard a loud "pop" kinda sound!!??!! any idea? it was in the engine for sure!!
     
  16. AllMotorMonster

    AllMotorMonster Senior Member

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    I'll second it...

    -Make sure the engine is at normal operating temps
    -Remove the ecu
    -Remove all spark plugs
    -Remove the intake
    -Open the throttle 100%
    -Crank 5-6 times
    -Record the number
    -Move to the next cylinder

    Reinstall all items, go for a drive again and get engine up to temps

    Restart process above, and record the numbers, then take the average

    This gives you the most accurate readings.

    HTH
     
  17. swapdohc

    swapdohc Member

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    No fuel, wide open throttle and a strong battery. Then crank it until it is done pumping up. done.
     
  18. shithatch

    shithatch Junior Member

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    u only have to let it turn over 4 times.... it is a 4 stroke engine!
     
  19. 69crx69

    69crx69 Member

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    What would be the ideal psi that you should get when doing a compression test?And what is the max variation between cylinders?(I.E. 10psi or 15psi and so on.)
     
  20. B16

    B16 Super Moderator VIP

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    dont worry about the psi reading, as long as all 4 are within 10% of each other, then you're fine.
     
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