Komatsu PC600-8 No Boost Pressure

Engine in the machine is the Komatsu SA6D140. It has a common rail fuel system. No DPF or pollution stuff and no waste gate on the turbo. Fuel cooled ECM mounted on the side of the engine. No electrical codes and only old mechanical codes. Fuel filters have been replaces and all connections checked for screens.

Power is good for awhile after first start. Complaint was that machine would lose power and drag the motor down to stopping at times. Issue is sporadic. We checked and adjusted the hydraulic pumps output so as to make the machine operate and prove the hydraulic pumps weren't causing the problem. Checked turbo boost and when running right, it is at about 220 KPA which is about 32 PSI. When not running right boost was 77 KPA which is about 12 PSI. Checked it without air cleaners and same result. Pulled intake side and rotor seemed to turn OK. Fins in impeller were a little chewed on the input edges but there were no marks on the circumference of the housing. We couldn't shut the pipe crew down so put it back together, ordered a turbo charger and are just waiting for a time when we can have the machine for a day or two.

My question is can anyone think of anything else we should check? They know I have little experience with this engine and its software.

John,

Easy check I like to do is key on, engine off, observe all the engine pressure and temp sensor values with the software to confirm they are reading accurate or realistic base values.

A sensor may be erroneous, but still in range, so no code.

Next, try spraying soapy water on the cooler and all the air connections. Maybe double-check for a boost leak?

Atmospheric pressure sensor reading wrong can cause low power, I would also be curious about the fuel pressure even if filters are good, I have seen things in the tank that I wouldn't expect randomly plugging the inlet.

John C. said:

...Checked turbo boost and when running right, it is at about 220 KPA which is about 32 PSI. When not running right boost was 77 KPA which is about 12 PSI...

Click to expand...

This value of turbocharger is good at 220 kPa.
and of course, the turbo pressure will drop as the engine speed decreases. It only got 77kPA because the engine speed was already reduced a lot.

Supply hoses from the fuel tank were replaced with new hoses. Fittings and fuel supply pump were replaced. Tank level was run low enough to see the bottom of the tank. No trash. Fuel supply problems were ruled out.

Checks on the senders were run and nothing seemed to be wrong. I did not record or note them as it didn't occur to me while in the heat of battle. I have noted the suggestions here of the sensors and will check if the issue shows again. Thanks for that info.

Turbo boost when the engine was running properly was the 220 KPA when under load. When the problem showed up the boost would not go over 77 KPA loaded or not. All that made sense at the time was a problem in the turbo charger. A new one was installed last Thursday. Boost went back up to 220 KPA and the power problem went away. The mechanic who installed the new turbo said there was no damage seen in the old one. He turned the impeller on the new one and it felt nearly the same as the old one. He pre-lubed the new one and it spun a lot easier.

The old turbo appeared to be original with the machine. Machine hours were about 7,800. In my experience with Komatsu engine, the turbo chargers were good for around 5K to 7K hours. I figured it was a better chance of a problem with this unit given operating time. The big question was the usual symptoms of lots of black smoke or noise and vibration were not present. All we can figure is that the loss of boost was sensed by the ECU and fuel was cut back to prevent black smoke similar to what the old aneroid valves used to do in pre Tier engines.

Unfortunately, we had to take an educated stab in the dark that this component was bad. I still have that slight bit of doubt in my mind about the way we went about finding the problem. Has anyone else found a turbo showing no damage or symptoms of failure that would not spin up in normal operation?