Cummins ISB 6.7 no-start

This week we worked on a Cummins ISB 6.7L engine. This is a demonstration engine on loan to us from Cummins in our school's shop and not mounted in-vehicle. The complaint is cranking but no-start.

Our first test was checking open circuit battery voltage, which measured 1.2V. As this engine had not been run in a while, we also made other checks such as making sure that it had sufficient fuel. After charging the battery we had the same starting issues.

The engine fault lamp was illuminated so our next step was to pull the fault codes. Unfortunately, our scan tool encountered technical issues so we were not able to hook it up. Instead, we referred to service information and pulled the codes by flipping the diagnostic switch and flashing the codes. Service information indicated this would either be a dash-mounted switch or in some cases pedal-operated.

On our engine, the codes are flashed first by the amber warning lamp illuminating, followed by the red stop lamp flashing. Consecutive flashes are counted, followed by a pause, and the next set of consecutive flashes are counted. This is done until the amber warning lamp illuminates again, at which point you have read the code. The same code is then repeated, before moving on to the next code. We counted the codes in this manner until the first code recorded was repeated, then we looked up fault codes in the service information.

According to service information and the fault codes we had pulled, we had several electrical circuits, including the accelerator pedal position sensor, and fuel pump pressurizing assembly (which is pulse width modulated fuel pump actuator controlled by the ECM). We also had a code for the electronic fuel injection control valve circuit.

We tested for voltage making it to the fuel pump actuator (see video below). Key-on voltage was 6.8V, which dropped to around 3.5V when hooked to the actuator connector. There was also .7V on the connector with the key off, there should be 0. We jumped the actuator and put a full 12V to it and we could still not start the engine. We also tested the accelerator pedal position sensor circuit and found it to be working as intended.

We will continue working on this problem and find the root cause of our no-start condition.

Some thoughts on what I learned this week:

Once again we are rooted in the service information, wiring diagrams, and electrical diagnostic procedures that are a standard part of servicing modern vehicles. This will only increase in the future. Whether it's a gasoline or a diesel engine, everything from the fuel pump to the injectors is electronically controlled. While we will always have wrenches and flashlights in our toolbox, some of the most important tools at our disposal are a laptop/scan tool, service information including electrical wiring diagrams, and a good functioning DVOM.