Low Power with No engine codes is a tough problem to have because of the lack of information which generally comes from reading an engine code. A lot of times a code will point you in the right direction and give you a general idea what area of the engine to look at.
In this case we just started to inspect the emission side of the engine beginning with the intake system and compressor side of the turbocharger. The compressor wheel had a slight layer of soot build up but nothing severe. We used combustion cleaning spray to clean up the wheel and it really did the trick but the fumes were hard to take. (Doors open and fans on)
Another area was the boost and temperature sensors on the driver’s side below the intake throttle and EGR valves. Both were fairly clean so the EGR which is surrounded constantly by hot exhaust gases was the next best choice. The EGR funnels cooled exhaust gases into the intake which helps reduce harmful emissions called NOx (oxides of nitrogen).
It does not take much to remove the EGR because of the easy access but this one was tight. Using a bar we had to loosen the flange side to side and pry it out of the housing. Once removed we saw that the valve was stuck open. This was definitely causing the lack of power bypassing exhaust directly to the intake.
We could have used the valve after cleaning it up. The main problem was the EGR throttle shaft hooked to the electric motor was sticking and it had to be loosened up. I didn’t want to take any chances so I bought a new EGR from the dealer. Surprisingly it was not that expensive….since there was no core charge we kept the old EGR for a spare in case we need one in a pinch.
Once replaced the horsepower was back. It was strange that there were no engine codes especially if the EGR was stuck in one position. The on board computer works with percentages when opening and closing the valves on the EGR so one would think that if the program that runs the engine noticed a wrong percentile it would flip a code. Regardless of that the problem got repaired and everybody is happy.
This is another experience that we can register in our brains for the next time. If a Maxxforce DT diesel engine in our fleet experiences low power with no codes we will be pursuing the same areas we looked at for this fix. As a matter of fact there is another bus in our fleet with similar problems. Experience has paid off once again.