MEP804A Overspeed Trip

[vwgilmer]

My son and I are working on an MEP804A with the Isuzu diesel. When we got the unit a few weeks back, it would not start. Starter would spin the motor but not fire. After several hours of troubleshooting, we found that the fuel suction hose had tiny hairline cracks and was letting air in. Long story short, it took forever to get all the air out of the system. Then we found that there was water everywhere in the fuel system. I drained around 5 gallon of water. We filled the tank with new fresh fuel and went back to starting it. The unit finally started. Then after the engine stopped "shuttering" and wanted to run smooth, the thing would start and immediately rev wide open then get an overspeed warning light come on the control panel. This happens every time within 2 seconds of starting. I found a manual on here for this unit that was a -24 level that had some good troubleshooting info. My son adjusted on the governor control as stated in the manual for a while but no luck. He finally got to speak with a sargeant in a unit that actually works on generators. He told my son he would need a -34 level manual. I have not been able to find a manual ending in -34. My son is in the Va National Guard. His MOS is Heavy Equipment mechanic and I am a civilian mechanic. We are really beating our heads trying to figure this one out. Is that manual available on here? Any help you can give will be greatly appreciated.

 

[Guyfang]

Your son needs to talk to someone who knows generators. There is no -34. The -24 is it. Try taking the electric Actuator off and seeing if the linkage is hooked up right.

 

[kloppk]

Is the mag pickup (MPU) adjusted properly and providing 2-3 volts AC across GC terminals 16 & 17 when dead cranking the engine?

According to the info below the DC voltage across GC terminals 9 & 10 may give a clue. This is the voltage sent to the actuator to control engine RPM.
When initially cranking the engine the voltage there should be 16 - 17 volts DC. This is setting the actuator to a nominal starting position.
Once the engine has started the voltage there should drop to 7-8 volts for no load running. This is setting the actuator to a nominal no load position.
20 - 21 volts indicates the GC is not receiving the MPU signal and the GC is compensating by going to max output.

 

[vwgilmer]

Your son needs to talk to someone who knows generators. There is no -34. The -24 is it. Try taking the electric Actuator off and seeing if the linkage is hooked up right.

My son said he had never heard of a -34 manual as well. He is going to try to talk with one of the actual generator mechanics. We will take the actuator off and check everything. We know that the actuator is working but you are right the linkage could have a problem. Thank you so much for your reply.

 

[vwgilmer]

Is the mag pickup (MPU) adjusted properly and providing 2-3 volts AC across GC terminals 16 & 17 when dead cranking the engine?

According to the info below the DC voltage across GC terminals 9 & 10 may give a clue. This is the voltage sent to the actuator to control engine RPM.
When initially cranking the engine the voltage there should be 16 - 17 volts DC. This is setting the actuator to a nominal starting position.
Once the engine has started the voltage there should drop to 7-8 volts for no load running. This is setting the actuator to a nominal no load position.
20 - 21 volts indicates the GC is not receiving the MPU signal and the GC is compensating by going to max output.

View attachment 941169

We will check this voltage. Thank you for the reply.

 

[Guyfang]

Often, someone can not get the set to start. They think that the Actuator is the problem. So it gets removed. Then incorrectly installed. Has anyone ever seen this set run right?

More often its the MPU, as Kurt highlighted in his message.