How Do Toyota Fuel Injectors Work?

Introduction

Toyota fuel injectors are an electro-mechanical device that meters, atomizes and directs fuel into the intake manifold. Toyotas use 40 to 50 pounds constant fuel pressure. When they are working well, they should hold a pressure of at least 25 pounds for five minutes with the engine off. They use an internal resistance in the windings to keep the injectors cool when in operation.

Injectors have power continuously with the key on. The computer uses the signal from the crank and cam sensor, mass air flow sensor, coolant temperature sensor, intake air temperature, map sensor, throttle position sensor and the oxygen sensors to formulate the necessary on-time for the injectors in real time. The computer has injector driver circuits that operate the injectors by grounding their circuit for a specific period of time, which is its planned engine management for the specific environment and situation at the very moment. It makes changes many times a second to maintain a 14.5:1 mixture air and fuel, respectively.

The longer the computer grounds the injectors, the longer they are open and the more fuel is delivered. All fuel injectors on all cars, with the exception of diesels, work exactly the same. When an engine is started the computer (ECM) uses the crank sensor to tell it where top dead center is for the ignition. The ECM uses the cam sensor to adjust the sequential fuel injection, the coolant temperature sensor to see if the engine is hot or cold, the throttle position sensor to see how much the accelerator is being depressed and the mass air flow sensor to determine the amount of air moving into the manifold. The air moving into the manifold changes with temperature and altitude. The ECM also the intake temperature sensor to determine the temp of incoming air and finally the oxygen sensor to determine if the mixture is correct. From all this information, it will adjust the injector on time to deal with the demand.

To check an injector to see if it is performing within parameters, check it with the engine running and listen to it with a long thin screwdriver to your ear or use a mechanic's stethoscope. It should have a regular sound with no drop offs or hesitations. The next test is to remove the electrical connector on one fuel injector at a time and watch the drop in RPM. They should all have a uniform drop in RPM. If one is suspect shut the engine off and disconnect the electrical connector on the suspect injector. Use an ohmmeter and check across the terminals of the injector. Acceptable limits are from 13 to 15 ohms. If not in the limits, replace the injector.