2. Clean the candle niches of dirt and debris. Turn out the candles.
3. Disconnect the electrical connector on the carburetor to prevent the fuel cut off solenoid valve from operating.
4. On models 3.0 l disconnect an electric socket of the distributor for the purpose of deenergizing of system of ignition.
5. On 4.2L models, to de-energize the ignition system, disconnect the positive wire from the coil. Seal the end of the wire with tape to prevent accidental short circuits.
6. Install a compression tester in the spark plug socket of the first cylinder (see accompanying illustration) (follow the instrument manufacturer's instructions).
7. Have an assistant fully open the throttle and turn the engine over with the starter. After reading the maximum meter reading (usually this is achieved on the third or fourth revolution of the engine) starter can be turned off.
8. Record the result and repeat the test for the remaining cylinders.
9. Compare all the readings taken with each other (the required values and the allowable difference between the cylinders are given in tables of sizes and adjustments at the end of the guide).
10. If the compression pressure in one or more cylinders is too low, perform the following additional check:
- Pour into the appropriate spark plug hole (I) a small amount of engine oil, for even distribution of oil in the cylinder (Oh) check the engine.
- Repeat the compression pressure test for that cylinder (ov).
A significant increase in compression pressure after filling the cylinder with oil is a sign of wear or damage to the piston rings, piston or cylinder bore.
The absence of any noticeable change in readings can be considered as a sign of jamming, burning, or damaged valves or a leak in the cylinder head gasket.
Late Years 4.2L Models Equipped with Fuel Injection (EFI)
1. Start the engine and warm it up to normal operating temperature. Switch off the ignition.
2. Relieve pressure in the supply system.
3. Remove the air cleaner element and spark plugs.
4. Disconnect the BB wire of the ignition coil from the distributor cap and ground it to ground.
5. Install the compression gauge in the spark plug hole of the first cylinder (follow the instrument manufacturer's instructions).
6. Have an assistant open the throttle fully and crank the engine with the starter until the maximum gauge reading is reached (Usually three or four turns are sufficient).
7. Record the reading and repeat the test for the remaining cylinders.
8. Compare all the readings taken with each other (the required values and the allowable difference between the cylinders are given in tables of sizes and adjustments at the end of the guide).
9. If the compression pressure in one or more cylinders is too low, perform the following additional check:
- Pour into the appropriate spark plug hole (I) a small amount of engine oil, for even distribution of oil in the cylinder (Oh) check the engine.
- Repeat the compression pressure test for that cylinder (ov).
A significant increase in compression pressure after filling the cylinder with oil is a sign of wear or damage to the piston rings, piston or cylinder bore.
The absence of any noticeable change in readings can be considered as a sign of jamming, burning, or damaged valves or a leak in the cylinder head gasket.