Cat 3116 Troubleshooting No Power

The problem with this 3116 Cat Diesel Engine was no power. The funny thing was it felt like someone stuck a banana in the tailpipe. There was no engine miss or hesitation what so ever. I checked for excessive back-pressure and that was normal.

One thing that seemed curious was the rpms in neutral went to the maximum without any problem but as soon as you put a load on the engine the rpms stayed at around 1200 rpm with no torque at all.

The Cat 3116 Governor controls the fuel rack which in turn decides how much fuel to allow to the injectors according to engine load and speed. The operator controls the throttle and the load is read off of the turbo boost pressure. The boost line goes directly to the governor air fuel ratio control. The more boost, the governor moves the rack for more fuel.

I tested the air/fuel ratio diaphragm with a regulator on the bus and it was leaking into the housing meaning the diaphragm had failed. Once I replaced the diaphragm it was a no-brainer to retest the new assembly and check for leaks. The new diaphragm was holding nicely.

NOTE: Don't test diaphragm over 20 psi

Here is a picture of the old diaphragm with a split in it. I remember the red flag that popped into my head when I called the Cat dealer for this part and they had 3 diaphragms on the shelf. Perhaps a recurring problem?

The 3 allen head screws are removed to pull the cover off to replace the diaphragm. This is an easy procedure once the governor is removed from the engine.

The governor linkage must be unhooked from the fuel rack before removing. Here you can see the pin which slides into the linkage and secured with a C clip.

The governor does not have to be timed and is fastened to the engine with 3 m8 bolts. Not much to it once all the fuel lines and piping is removed. This was a case of a smooth No Power situation. There was no white or black smoke, the engine did not miss or do anything really obvious. Testing the diaphragm with the air regulator is just another way for a diesel mechanic to troubleshoot a Cat 3116 Diesel Engine.