MEP-804A Engine starts but stops when MASTER SWITCH is released from START position

[BadRobot]

I have MEP-804A for over a year now. It started and ran fine. I tried to start it today.
1. There are no fault indicator. All lights are lit when press the test button and go off when release the button,
2. When the master switch is in prime/auxiliary fuel, I can hear the fuel pump.
3. When the master switch is in prime/run, I cannot hear the fuel pump. I used to hear it before.
4. When the master switch is in start position, the engine run but it stop when release the master switch from start position. I hold the master switch in start position until 25 psi.

The fuel is almost full tank. The fuel pump seems to functioning.

What's seem to be the problem?

Any advises / suggestions are greatly appreciated.
​

 

[DieselAddict]

In addition to going through the troubleshooting section of the TM I would for sure say to check the low oil pressure switch.

 

[robertsears1]

The 804a has a mechanical main fuel pump—should be no sound in prime & run position. I would also suggest holding the start position longer, perhaps until the oil pressure levels off, it will not hurt anything. I have a 003a and I have to hold it around 15” after oil pressure comes up or it starts to shut down as I release the switch. I know what to listen for and catch it every time now.

Make sure to do the quad modification if yours has not been done.

Robert

 

[BadRobot]

Thank you everyone for your suggestions.

I think I know what's wrong. The oil presuure guage indicates high pressure (it points all the way to the high side). I think I will replace the oil pressure sending unit, first. Then the oil pressure guage.

Now the hunting for parts begin. I am not sure that it uses the same oil pressure sending unit as MEP-803A but I will confirm with part number in TM.

 

[Guyfang]

The oil press sending unit has no function other then to make the meter move. The LOP, Low Oil Pressure Switch is what tells the gen set to not run after you let the S1 return to the run position. In turn, the idiot light should come on. To test the LOP, start the set, hold the S1 up, flip the battle short switch up, and let the S1 go. Still running? Then the LOP is suspect.

How owe many hours on the set?

 

[robertsears1]

Here is a picture of my MEP 804a running. It took about 8” to get to that pressure on startup. The reason the batteries are charging so hard is because I left the battery depletion devices (panel lights) on last week. I was dismayed when I went to start it and the batteries acted flat. After jumping it and looking around, I noticed that switch in a non-standard position.

I wanted to let things charge and put a little load on the generator, so I plugged in a FDECU-5 and nothing. Then I plugged in another one that was giving me trouble recently and it is working like a charm! It is very rare that this 804a will run the FDECU without showing a short, usually I have to use the 804b. Maybe my DeOxit is working on this unit also.

 

[BadRobot]

The oil press sending unit has no function other then to make the meter move. The LOP, Low Oil Pressure Switch is what tells the gen set to not run after you let the S1 return to the run position. In turn, the idiot light should come on. To test the LOP, start the set, hold the S1 up, flip the battle short switch up, and let the S1 go. Still running? Then the LOP is suspect.

How owe many hours on the set?

I will test it out when I get home today.

The GenSet has 7 hrs. I got it when it had 2.1 hr.

​

 

[Light in the Dark]

Here is a picture of my MEP 804a running. It took about 8” to get to that pressure on startup. The reason the batteries are charging so hard is because I left the battery depletion devices (panel lights) on last week. I was dismayed when I went to start it and the batteries acted flat. After jumping it and looking around, I noticed that switch in a non-standard position.

I wanted to let things charge and put a little load on the generator, so I plugged in a FDECU-5 and nothing. Then I plugged in another one that was giving me trouble recently and it is working like a charm! It is very rare that this 804a will run the FDECU without showing a short, usually I have to use the 804b. Maybe my DeOxit is working on this unit also.

This is why I always set the dead crank to off, as a matter of habit. To me, its a lot like shutting off the 20lb propane tank in your grille... only takes once to have the device not work when you need it to over something silly.

 

[robertsears1]

Good point, thanks.

Robert

 

[BadRobot]

The oil press sending unit has no function other then to make the meter move. The LOP, Low Oil Pressure Switch is what tells the gen set to not run after you let the S1 return to the run position. In turn, the idiot light should come on. To test the LOP, start the set, hold the S1 up, flip the battle short switch up, and let the S1 go. Still running? Then the LOP is suspect.

How owe many hours on the set?

This is the steps I took.
1. Turned the master switch to prime / run.
2. Turned the master switch to start. The engine started and ran.
3. Turned the master switch to run and let the master switch returned to prime / run position.
4. The engine continued to run.

What is the conclusion? Is the LOP dead? Can it be cleaned as in TM?

Note: oil pressure guage was moved at all. It may be struck but I will change the oil pressure guage and oil sending unit anyway.

Another steps I took.
1. Turned the battle short switch up.
2. Turned the master switch to prime / run.
3. Turned the master switch to start. The engine did not start.

 

[Guyfang]

This is the steps I took.
1. Turned the master switch to prime / run.
2. Turned the master switch to start. The engine started and ran.
3. Turned the master switch to run and let the master switch returned to prime / run position.
4. The engine continued to run.

What is the conclusion? Is the LOP dead? Can it be cleaned as in TM?

Note: oil pressure guage was moved at all. It may be struck but I will change the oil pressure guage and oil sending unit anyway.

Another steps I took.
1. Turned the battle short switch up.
2. Turned the master switch to prime / run.
3. Turned the master switch to start. The engine did not start.

Go back to post #5. Read how I told you to use the Battle short switch. Compare my instructions to what you wrote above. See the difference?

Read in the -24 manual how to check and test the Gage. And get a seperate pressure Gage, to hook up independently to confirm that your sending unit is bad. Don't throw parts at it, troubleshoot it.

 

[BadRobot]

This is your instruction, "To test the LOP, start the set, hold the S1 up, flip the battle short switch up, and let the S1 go. Still running? Then the LOP is suspect.". The engine still continue to run after flip the battle short switch.

I will try to clean the LOP based on TM first before I replace it. TM 9-6115-643-24, page 2-146.[SUB][SUP]
[/SUP][/SUB]​

 

[Guyfang]

And you wrote:
1. Turned Battle Short up.
2. Turned the Master Switch to Prime/Run.
3. Turned the Master Switch to start. The engine did not start.

Thats different then what I wrote. The engine can not start unless the Battle Short is turned on AFTER the set is running, and the S1 is held in the Start position. Think about it. When you place the S1 in the start position, the engine turns over, and starts. It starts because the S1 also bypasses all the safety's, like low oil pressure, for instance. So once it's running, with the S1 still in the run position, Then apply the Battle short switch, and let S1 go. The set is designed to NOT start with the Battle Short in the on position. Only when the set is running, can you engage the Battle Short, to keep it running.