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Tristan Franklin
Tristan Franklin, MASTER ASE CERTIFIED
Category: Car
Satisfied Customers: 1612
Experience:  8yrs. exp. engine repair performance brakes electrical air condition
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1998 ford ranger 2.5 four cylinder. compression on cly 1-3

Resolved Question:

1998 ford ranger 2.5 four cylinder. compression on cly 1-3 had 160 psi comp.#4 o psi. Removed head gasket ok had head rebult at machine shop they pressured tested under heat checked ok. Put head back on. Ran compression test same results as before # XXXXX o psi piston looked ok so did cylinder walls. Im at a loss as what to do next. Help
Submitted: 8 years ago.
Category: Car
Expert:  Tristan Franklin replied 8 years ago.

here is the procedure and this will tell you what the problem is. good luck. i hope i helped and please accept my answer. thanks T-MAN

 

  1. Ensure that the vehicle batteries are in good condition, and fully charged.
  2. Operate the vehicle until the engine is at normal operating temperature.
  3. Disconnect the positive ignition coil wire plug from the ignition coil.
  4. Disconnect the fuel injector electrical connector.
  5. Remove all of the spark plugs.

    Notice: Do not insert objects into the throttle plate opening. Damage to the throttle body can result, requiring replacement of the throttle body assembly.

  6. Block the throttle linkage wide open.
  7. Install the engine cylinder compression gage to the cylinder being tested.
  8. Using the vehicle starter motor, rotate, or crank the engine for 4 compression strokes, or puffs, for the cylinder being tested. If the engine rotates for more than 4 compression strokes, test the cylinder again.
  9. Record the compression reading.
  10. Remove the engine cylinder compression gage from the cylinder being tested.
  11. Repeat steps 8-11 for each additional cylinder. All cylinders must be tested to obtain valid test results.
  12. If any cylinders have low compression, inject approximately 15 ml (1 oz) of engine oil into the cylinder through the spark plug hole.
  13. Repeat steps 8-11 for all low compression cylinders.
  14. 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). Multiply the highest cylinder pressure by 70 percent, 1035 kPa x 70 percent = 725 kPa (150 psi x 70 percent = 105 psi), in order to determine the lowest allowable pressure in any other cylinder.
    Normal
    The compression builds up quickly and evenly to the specified compression.
    Piston rings leaking
    Compression is low on the first compression stroke. The compression builds up on the following strokes, but does not reach normal. Compression improves considerably when you add oil.
    Valves leaking
    Compression is low on the first compression stroke. The compression does not build up on the following strokes, and does not reach normal. Compression does not improve much, if at all, when you add oil.
    Head gasket leaking
    Compression is low on the first stroke. The compression does not build up on the following strokes, and does not reach normal. Compression does not improve much, if at all, when you add oil. Adjacent cylinders have the same, or similar, low compression readings.
  15. If one or more cylinders fails to meet the minimum specified compression, repair or replace all damaged or worn components and test the engine again.
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