Engine Performance

If a loss of performance is noticed, ignition timing should be checked. If ignition timing is retarded by 9, 18 or 27° indicating 1, 2 or 3 (timing belt) teeth may have skipped, then, camshaft and accessory shaft timing with the crankshaft should be checked.

To provide best vehicle performance and lowest vehide emissions, it is most important that the tune-up be done accurately. Use the specifications listed on the Vehicle Emission Control Information label found in the engine compartment.

1. Test cranking amperage draw. See Starting Motor/Testing and Inspection.
2. Tighten the intake manifold bolts to specifications.
3. Perform cylinder compression test.
a. Check engine oil level and add oil if necessary.
b. Drive the vehicle until engine reaches normal operating temperature.
c. Select a route free from traffic and other forms of congestion, observe all traffic laws, and accelerate through the gears several times briskly.

CAUTION: Do not overspeed the engine. The higher engine speed may help clean out valve seal deposits which can prevent accurate compression readings.

d. Remove all spark plugs from engine. As spark plugs are being removed, check electrodes for abnormal firing indicators fouled, hot, oily, etc. Record cylinder number of spark plug for future reference.
e. Disconnect coil wire from distributor and secure to good ground to prevent a spark from starting a fire (Conventional ignition system). For Direct Ignition System (DIS) disconnect the coil connecter.
f. Be sure throttle blade is fully open during the compression check.
g. Insert compression gage adaptor into the #1 spark plug hole in cylinder head. Crank engine until maximum pressure is reached on gage. Record this pressure as #1 cylinder pressure.
h. Repeat Step G for all remaining cylinders.
i. Compression should not be less than (689 kPa) 100 psi and not vary more than 25 percent from cylinder to cylinder.
j. If one or more cylinders have abnormally low compression pressures, repeat steps 3b through 3h.
k. If the same cylinder or cylinders repeat an abnormally low reading on the second compression test, it could indicate the existence of a problem in the cylinder in question.

NOTE: The recommended compression pressures are to be used only as a guide to diagnosing engine problems. An engine should not be dis assembled to determine the cause of low cormpression unless some malfunction is present.

4. Clean or replace spark plugs as necessary and adjust gap as specified. Tighten to specifications.
5. Test resistance of spark plug cables. Refer to Ignition System Secondary Circuit Inspection.
6. Inspect the primary wire. Test coil output voltage, primary and secondary resistance. Replace parts as necessary. Refer to Ignition System and make necessary adjustment.
7. Ignition timing should be set to specifications. (See Specification Label in engine compartment).
8. Test fuel pump for pressure.
9. The air filter elements should be replaced as specified in Maintenance.
10. Inspect crankcase ventilation system as out lined in Maintenance. For emission controls see Emission Controls Systems for service procedures.
11. Inspect and adjust accessory belt drives referring to Accessory Belt Drive for proper adjustments.
12. Road test vehicle as a final test.