Diagnostic Aids
Using "Scan" tester, observe the block learn values at different engine speeds. If a Code 45 exists, the block learn values will be around 115.
- Fuel system will go rich if pressure is too high. The ECM can compensate for some increase. If pressure gets too high, however, a Code 45 may be set.
- Check for fuel contaminated oil.
- If an open occurs on circuit No. 453, HEI induced electrical "noise" may result, causing simulated reference pulses to be picked up by ECM on the reference line of the 4-wire EST harness. The additional pulses result in a higher than actual engine speed signal. The ECM will increase injector pulse width ("on" time) to match fuel requirements of the increased RPM signal. "Scan" tester will show higher than actual RPM, which can help in diagnosing this problem.
- Check charcoal canister for fuel saturation. If full of fuel, check canister control and hoses.
- An output that causes the ECM to sense a lower than normal vacuum can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM to set a fixed value for the sensor. Substitute a different MAP sensor if the rich condition is gone while the sensor is disconnected.
- An intermittent TPS output will cause the system to go rich due to a false indication of engine acceleration.
For intermittent inspection procedures, refer to INTERMITTENTS under TESTS W/O CODES - EFI article.