Cylinder Balance Test

Discussion in 'Fox 5.0 Mustang Tech' started by JBeenken, Apr 9, 2007.

  1. How do you do a cylinder balance test? Please be specific on what to do as I am totally clueless on how to do this!
  2. If you have a star tester, after it goes through the normal steps for reading codes...and starts flashing any codes you may have. You need to goose the throttle, just quickly pop the pedal to WOT. The star tester will do the rest, you will hear the engine rev up and one by one it will cut spark to each cylinder. After it goes through that cycle, it will flash a code...telling you which cylinder is having a problem or if no problem was found.
  3. What is a star tester is that something that you can rent at auto zone?
  4. A repair manual is always helpful. The internet has things like Alldata but Stangnet has AllknowingJrichker instead. :D

    If you search his posts, you will find his cylinder balance test write-up. I recalled that he just posted his info within the last day or so.

    Good luck.
  5. Cylinder balance test:
    Warm the car's engine up to normal operating temperature. Use a
    jumper wire or paper clip to put the computer into test mode. Start
    the engine and let it go through the normal diagnostic tests, then
    quickly press the throttle to the floor. The engine RPM should exceed
    2500 RPM's for a brief second. The engine RPM's will increase to about
    1450-1600 RPM and hold steady. The engine will shut off power to each
    injector, one at a time. When it has sequenced through all 8 injectors,
    it will flash 9 for everything OK, or the number of the failing cylinder
    such as 2 for cylinder #2. Quickly pressing the throttle again up to
    2500 RPM’s will cause the test to re-run with smaller qualifying figures.
    Do it a third time, and if the same cylinder shows up, the cylinder is
    weak and isn’t putting out power like it should. See the Chilton’s Shop
    manual for the complete test procedure

    Here's the link to dump the computer codes with only a jumper wire
    or paper clip and the check engine light, or test light or voltmeter.
    I’ve used it for years, and it works great.



    IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

    For those who are intimidated by all the wires & connections,
    see for what a
    typical hand scanner looks like. Normal retail price is about $30 or so
    at Walmart.

    Or for a nicer scanner see – It has a 3 digit LCD display so that you don’t have to count flashes
    or beeps.. Cost is $33.

    Do a compression test on all the cylinders.
    Take special note of any cylinder that shows up as weak in the cylinder
    balance test. Low compression on one of these cylinders rules out the
    injectors as being the most likely cause of the problem. Look at cylinders
    that fail the cylinder balance test but have good compression. These
    cylinders either have a bad injector, bad spark plug or spark plug wire.
    Move the wire and then the spark plug to another cylinder and run the
    cylinder balance test again. If it follows the moved wire or spark plug,
    you have found the problem. If the same cylinder fails the test again,
    the injector is bad. If different cylinders fail the cylinder balance test,
    you have ignition problems or wiring problems in the 10 pin black &
    white electrical connectors located by the EGR.

    How to do a compression test:
    Only use a compression tester with a screw in adapter for the spark
    plug hole. The other type leaks too much to get an accurate reading.
    Your local auto parts store may have a compression tester to rent.
    If you do mechanic work on your own car on a regular basis, it would
    be a good tool to add to your collection.

    With the engine warmed up, remove all spark plugs and prop the
    throttle wide open, crank the engine until it the gage reading stops
    increasing. On a cold engine, it will be hard to tell what's good &
    what's not. Some of the recent posts have numbers ranging from
    140-170 psi. If the compression is low, squirt some oil in the cylinder
    and do it again – if it comes up, the rings are worn. There should be
    no more than 10% difference between cylinders. Use a blow down
    leak test (puts compressed air inside cylinders) on cylinders that
    have more than 10% difference.

    See the link to my site for details on how to build your own blow
    down type compression tester.