November 1, 2002
Peter Mc Ardle -- Asian Specialist
Nissan Cars & Trucks Hard Start/No Start
Virtually all fuel injected Nissans receive a "cranking "input signal to the ECM. This signal, which is a constant 12-volt input, is provided through the "ST" terminal of the ignition switch while the...
Virtually all fuel injected Nissans receive a “cranking “input signal to the ECM. This signal, which is a constant 12-volt input, is provided through the “ST” terminal of the ignition switch while the ignition switch is in the cranking position. This signal is used by the ECM to provide added fuel enrichment and increased ignition output for easier starting. If the ECM does not receive this input, the vehicle will be difficult to start, especially when the engine is cold. A quick check of the basics may reveal that you have good spark and fuel pressure, but weak or no injector pulse as indicated by noid light. Actually, in this case, the injector pulse is there, but it is so narrow that it may appear as weak pulse or not appear at all. In this situation, if you add fuel by spraying the intake with propane or carb cleaner, the vehicle starts and runs normally. Most likely there will be no trouble codes stored, and a check of the sensor inputs to the ECM, such as coolant temperature, crankshaft position, throttle position, air flow, as well as powers and grounds, reveal nothing abnormal. If this is your situation, then check the “cranking” input for proper values. Because this input is present only in the crank mode, some techs overlook this, or may not even be aware that it exists. On earlier models, most built prior to 1990, this input was wired directly to the ECM from the ignition switch and usually does not present a problem. On the later models, this input is usually provided through a fuse (labeled as “starting”) located in the fusebox. In this situation, either the fuse is open due to a shorted input wire to the ECM, or the fuse is missing because it was “borrowed” by someone to replace a blown fuse for the lights or the windshield wipers. The starting problem did not become apparent until the next morning when the engine was cold. If the vehicle exhibits hard starting when cold, and everything seems to be OK, don’t forget to check the cranking input signal. If the signal is missing, first verify whether the vehicle has a dedicated fuse for this circuit to start your diagnostics.