Preparation For Testing

The MCU system is capable of diagnosing some problems which may occur. To determine which components should be checked, perform the "Functional Test" which follows. If problems do exist, a service code will be displayed (as pulses on a voltmeter).

Locate the appropriate test chart and follow the repair procedure as instructed. DO NOT  use the test charts unless referred to them by the "Functional Test", or you may replace some components unnecessarily. Testing procedures require the following equipment:

• Dial Voltmeter (0-20v scale)
• Digital Voltmeter (DVOM - Min. impedance 10 megohms)
• Vacuum Gauge (0-30 in. Hg)
• Vacuum pump
• Tachometer
• Jumper Wire

1. Check vacuum hoses for leaks, cracks, or improper routing. Repair or replace as necessary.
2. Check electrical connections. Repair any frayed or broken wires. Ensure that all connections are clean and tight.
3. Check coolant level. Turn all accessories off. Place transmission in neutral and set parking brake. Warm engine to normal operating temperature. If air cleaner must be moved, leave all vacuum hoses attached. If engine will start, start engine and check for voltage at electric choke terminal.
   NOTE: If vehicle will not start, go to No Start Test (No. 1).
4. Turn ignition off. Locate Self-Test connector and insert a jumper wire between ground and Trigger sockets. Connect the positive lead of a needle-type voltmeter to vehicle battery positive terminal, and the negative lead to Self-Test output socket. Set voltmeter on 15-20 volt scale. Battery voltage may be shown.
5. Disable canister purge system by disconnecting the hose that runs from the canister to the purge valve (if equipped). Reconnect hose after testing. Make sure that the carburetor throttle linkage is off the high cam and that the choke is open.
6. On engines equipped with an EGR vacuum load control valve, plug the vent holes on the valve with a piece of tape. Remove tape after testing.