Engine Performance

To provide best vehicle performance and lowest vehicle emissions, it is most important that the tune-up be done accurately. Use the specifications listed on the Vehicle Emission Control Information label found on the engine compartment hood.
1. Test battery specific gravity. Add water, if necessary. Clean and tighten battery connections.
2. Test cranking amperage draw (refer to Starting and Charging for the proper procedure).
3. Tighten the intake manifold bolts (refer to Exhaust System for the proper specifications).
4. Perform cylinder compression test:

CAUTION: DO NOT overspeed the engine.

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 briskly accelerate through the gears several times. The higher engine speed may help clean out valve seat deposits which can prevent accurate compression readings.
d. Disconnect electrical connectors from coil towers and then remove coil towers.
e. 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.
f. Be sure throttle blades are fully open during the compression check.
g. Insert compression gauge adaptor into the No.1 spark plug hole. Crank engine until maximum pressure is reached on gauge. Record this pressure as No.1 cylinder pressure.
h. Repeat for all remaining cylinders.
i. Record the findings and compare them with the compression standards listed under Engine, Specifications.
j. If cylinder(s) have abnormally low compression pressures, repeat procedure.
k. If the same cylinder(s) repeat an abnormally low reading, it could indicate the existence of a problem in the cylinder.

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

5. Clean or replace spark plugs as necessary. Adjust gap.
6. Perform a combustion analysis.
7. Test fuel pump for pressure (refer to Powertrain Management for the proper specifications).
8. Inspect air filter element (refer to Maintenance for the proper procedure).
9. Inspect crankcase ventilation system (refer to Powertrain Management for the proper procedure).
10. For emission controls refer to Powertrain Management for service procedures.
11. Inspect and adjust accessory belt drives (refer to Drive Belts, Mounts, Brackets and Accessories for the proper adjustments).
12. Road test vehicle as a final test.