Poor Performance

Fig. 11 High energy ignition wiring circuit:

1. Poor performance related to the DEFI system is caused by either improper fuel delivery or incorrect spark advance timing. If fuel pressure of 9-12 psi is obtained during engine cranking, fuel delivery system is operating properly. If not, refer to ``Fuel System Diagnosis.'' Remove air cleaner and observe injector spray pattern while cranking engine. If spray pattern is not satisfactory, refer to ``Injector System Diagnosis.''
2. To check ignition timing, disconnect set timing electrical connector from HEI module and check ignition timing. Set timing to 10° BTDC and 800 RPM. If base timing is correct, the ability of the system to advance spark must be determined.
3. Since the ECM determines ignition advance based on many variables, it is not possible to establish reference points for ignition timing. However, if the system does advance, the shape of the advance curve can be assumed to be correct since it is determined by electronic circuitry which was able to recognize that some advance was required and did respond to this information. Reconnect set timing electrical connector and check timing. Timing should be between 20° and 30° BTDC at idle.
4. If ignition timing advances, proceed to step 6. If timing advance does not occur, a problem exists in the timing advance system. If voltage reading on HEI bypass circuit 462, Fig. 11, is zero volts, the HEI module operates in the bypass mode with 10° of spark advance at all times regardless of the spark advance signal from the ECM. If voltage reading on HEI bypass circuit is five volts, the HEI module accepts the spark timing signal provided by the ECM. To check voltage of circuit 462, disconnect four wire distributor electrical connector and measure voltage at harness connector pin C. If voltage reading is greater than four volts, replace the HEI module.
5. If voltage reading at circuit 462 is less than one volt, replace the ECM.
6. If ignition timing advances, check operation of EGR and air management systems. Refer to ``Performance Diagnosis'' under ``EGR Diagnosis'' and ``Air Management Diagnosis.'' Also, check air cleaner for restrictions and repair as necessary.
7. Check for vacuum leaks and binding of the throttle valve cable, throttle return spring and TPS, and correct as necessary. Enter diagnostic series .9.0 and ensure all parameters are within normal operating ranges.