May 1, 2002
Vince Walsh-Top Gun Technician
Nissan – Distributorless Ignition No Start/Misfire Diagnosis
Quite a few Nissans have distributorless ignition systems. This article will deal with 1987-89 Pulsars, and the 1990-94 300ZX. These systems are fairly similar. They both use a coil for each cylinder....
Quite a few Nissans have distributorless ignition systems. This article will deal with 1987-89 Pulsars, and the 1990-94 300ZX. These systems are fairly similar. They both use a coil for each cylinder. They also use a power transistor to trigger each coil’s primary circuit. These transistors are controlled by the ECM. Whether it is misfire or a no-start, the approach is the same. First, verify basic engine mechanical operation. If engine compression is OK, and any vacuum leaks have been ruled out, we must then isolate which cylinder(s) are not working. By unplugging each coil’s electrical three wire connector, one at a time, with the engine running, we will be able to isolate the dead cylinder(s). Do not leave this connector off too long or you really overload the catalytic converter with raw fuel which could cause a fire. Once the dead cylinder is isolated, the next step is to check that cylinder’s injector pulse with a noid light. Removal of the dead cylinder’s spark plug will usually reveal that the injector is working by being wet with fuel. If that is the case, then we must figure out why we do not have spark. Returning to the three-wire connector (refer to diagram), you should see that battery voltage should be present on the center wire with the key on. The second wire will be a constant ground (maximum voltage present should be no more than .050 volts). The third wire is the ignition coil ‘s primary circuit control. A quick check for a bad coil is to swap the suspect coil with a coil from a known good cylinder to see if the misfire moves with the suspect coil. If the misfire moves, you have found the problem. If the misfire stays, then continue reading. The next test will check to see if the ECM is controlling that coil’s primary circuit. The best way to do this is to use an oscilloscope or a multimeter that has the capability to measure frequency. At the power transistor (also known as the module or ignitor) there are two connectors. One end goes to the coils and the other end is to the ECM. At the ECM side of the harness of the power transistor, determine the primary wire of the coil that is not working. Using an oscilloscope, or a multimeter set for the frequency function, carefully back-probe this wire. With the engine cranking, you should see normal primary pattern on a scope; with a multimeter you should have between 1 and 2 hertz. If the signal is present, check your wire connections. If they are good, then replace the power transistor. You can verify your findings by using this next step. At the coil side of the harness, swap the wire in the connector from the suspect coil with the wire from a known good coil and restart the engine. If the misfire follows the wire from the misfiring cylinder, then replace the power transistor. Without getting into wire colours, a quick reference to the connector will indicate what measurements to make at each terminal. Resistance specs for the coils are: Primary .7 to 1.0 ohms; Secondary 8000 to 12,400 ohms.