How to Troubleshoot a Detroit Diesel Injector

by Jeff Woodward
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Fuel injectors are a primary component of all diesel engines. Fuel is drawn from the fuel tank and pushed by the fuel pump to the fuel injectors. The injectors then spray the diesel fuel into the cylinders, allowing the cylinders to fire. Prior to the late 1980s, fuel injectors were mechanical in nature. After the advent of the electronically controlled engine, fuel injectors became more advanced, relying on the engine's computer to tell them when to fire.

Basic Injector Troubleshooting

Step 1

Remove the bolts holding the valve cover to the engine block using a ratchet wrench and socket. Set the valve cover off to the side.

Step 2

Remove the exhaust manifold from the engine by removing the six hex-head bolts located at the front, middle and rear of the manifold. The exhaust manifold is located on the passenger side of the motor.

Start the engine. Watch the six manifold holes for smoke. A small amount of white smoke will be normal. If a manifold hole is not producing smoke, this may be an indicator that the injector on that cylinder is not firing.

Troubleshooting Injectors with a Prolink

Step 1

Start the engine and let it run until it reaches normal operating temperature.

Step 2

Plug the Pro-Link diagnostic reader into the Deutsch receptacle located under the drivers side dashboard. All make and model trucks are equipped with Deutsch receptacles since electronic engines were introduced.

Select "Cylinder Cutoff Test" from the list of options on the Pro-Link. Let the engine settle to 1000 rpm and perform cylinder cut-offs. The Pro-Link will indicate if an cylinder is not firing, indicative of a faulty injector.

Troubleshooting Injectors Using DDDL

Step 1

Start the engine and let it reach normal operating temperature.

Step 2

Plug a laptop computer into the Deutsch receptacle located under the drivers side dashboard. Run the Detroit Diesel Software DDDL7.0 program.

Step 3

Check for fault codes as listed on the diagnostic chart of the DDDL7.0 Detroit Diesel software, and repair or remove active and inactive codes first before proceeding to troubleshoot the injectors.

Perform dual and triple cylinder cut-off tests by turning off the cylinders using the Detroit Diesel DDDL7.0 software. Check the data acquired by reviewing the charts and information gathered from the cylinder cut-off tests by the Detroit Diesel software and comparing them to historic engine data as gathered from the software. A cylinder that failed to fire or was low in power is indicative of a failed injector.

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