Cummins N-14 thermostat reinstallation

This week was shop cleanup and doing whatever was needed to get our International and FLD trucks running again.

Our International has a Cummins N-14 in it and in a previous class we had removed the thermostat housing. Unfortunately the coolant hoses running from the thermostat to the air compressor and to the water pump were so badly rotted that they crumbled into pieces when we took them off. We therefore replaced the hoses with new lines and fittings and hooked everything back up. We also hosed down and scrubbed the shop floor.

Accessability is a problem sometimes.

Thermostat housing and hoses as we reinstalled them.

Cleaning the shop floor.

Some reflection on this week:

For mechanics and technicians of both cars and trucks, accessibility can range from good to an absolute nightmare. In the case of our thermostat housing, replacing the line we broke required removal of both lines and fittings off of the air compressor. Getting to the fitting on the water pump required use of a crow's foot wrench with a ratchet and extension as there was no room to get a normal wrench on it.

Cleanup is also an important aspect of working in a shop. Not only does it look unprofessional to have an unclean shop, it also presents a safety hazard to everyone who walks through it. Oil and coolant spilled all over the floor presents a slipping hazard. Tools or parts left on the floor are a tripping hazard. So take a little extra time and keep your work area clean!

Freightliner FLD N2 injector reinstallation

This week we returned to our Freightliner FLD and began reassembly. We replaced the O-rings on all the injectors we removed (3 per injector) before returning them to their bores. We cleaned out all bolt holes of oil to ensure we would not damage the engine when we torqued the bolts down. Then we reinstalled the rocker arm assemblies and the Jake brakes and torqued them down. We did not finish the full torquing procedure before the end of class, so we marked on our service information what we still had left to do.

Preparing to change O-rings on injectors. There are 3 for each injector.

Jake brakes have been reinstalled and are ready to be to be torqued.

Looking up our specs for torquing the Jake brakes.

Some thoughts on what I learned this week:

Torque, torque, torque. Especially with internal engine components, it is important to torque bolts to the values specified by the manufacturer. Whether on gasoline or diesel engines, failing to do so can lead to problems, premature failures, or damage to engine components. The torquing procedure for the Jake brakes calls for 40 ft-lbs on all bolts starting at the intake side. It then requires you to re-torque them to 100 ft-lbs on all bolts repeating the sequence.

Sometimes the torquing procedure may ask you to torque to a certain value, then back the bolt off a certain amount. You will also encounter procedures that call for torque angle (such as when torquing the head).

Properly torquing the bolts to manufacturer specification is just good practice that can save time and money avoiding possible problems and customer comebacks.

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.

Removal of N2 single-actuated EUI (electronic unit injectors)

This week's project was to remove the fuel injectors off of our FLD Freightliner. These injectors are N2 single-actuated EUIs (electronic unit injectors), which are bulkier than the newer N3 injectors.

In order to get the valve cover off, removal of the air filter housing and the radiator inlet hose off of the top of the valve cover was necessary. Afterwards we removed the valve cover, jake brake assemblies, rocker arm assemblys, and finally the injectors themselves. We removed the front 3 injectors from cylinders 1-3 (which I unfortunately did not remember to take pictures of)

Jake brake and rocker arm assemblies.

Valves and injector on cylinder #1.

Some thoughts on what I learned this week:

Care must be taken when removing the injectors as it is possible to spill fuel in the injector bore onto the piston. This can cause hydrostatic lock (too much non-compressible liquid in the cylinder which has no way to escape as the piston moves to top dead center on the compression stroke) and cause serious damage to vital engine components such as bending the connecting rod.

To prevent this, service literature recommends draining all the fuel from the cylinder head by removing both inlet and outlet lines at their fittings at the rear of the cylinder head and blowing low-pressure compressed air through the inlet fitting until all fuel has been purged from the cylinder head.

-Erik Miehrig