Voltage. One of the design parameters of the L-Jetronic system is that there must be 10 volts on the #10 pin connector at the ECU for the car to start. If there is less than 10 volts, the ECU shuts off. This requires a very good battery because the electrical load during starter cranking can cause the voltage to drop below 10 volts at the #10 pin. Check you battery condition and battery/ground connections first. Once you’ve determined that the battery and battery cabling are in good shape, try the following. From the #10 pin at the ECU connector, trace back into the harness (green/black wire) as far as possible. You will need a couple inches of wire. Cut the wire and tape it off going into the harness. Now, locate the main power relay next to the ECU. It has a large gauge red main power wire going into it. Take the wire from the #10 pin on the ECU and attach it to connector #87 on the main power relay. This provides more voltage to the starting circuit.

Fuel Pump Power. The combi-relay is the most common failure item in the L-Jetronic system. To test, unclip the airflow meter from the air filter housing.

Turn the key to the “on“ position, reach inside the airflow meter, and gently push the flap open. The fuel pump should click on, accompanied by the sound of fuel rushing through the fuel rail. If this does not happen, check the fuel pump fuse. If the fuse is intact, the culprit is most likely the combi-relay. On V6’s, the combi-relay is on the firewall, and the fuel pump fuse is in the fusebox. On Spiders, the fuse and relay are under the package shelf, behind the seats.

Cold Start Valve/Thermo Time Switch. The cold-start valve is supposed to supply a very rich mixture upon initial start up when cold. To test it, remove the cold start injector from the intake manifold, place the nozzle in a container to catch the fuel, and turn the key to the start position. With the temperature of the engine below 95 degrees, it should spray. If not, check for voltage at each of the two terminals on the injector with the starter activated. If one terminal has voltage but the other doesn’t, replace the cold-start injector.

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