mep8o2a low oil pressure shut down

[builmord]

the more I think I know about this gen the more I find out I don't. hope this makes sense to someone. reading a thread recently that talked about starting sequence to get oil pressure up before releasing the start position made me take a second look at the wiring to the oil pressure switch. there was only 1 wire attached and that was to the nc connection. found another wire that had been cut which I believe went to the c connection. this leaves the control circuit in the open position. testing the fault indicators shows all lights operable and system clear of faults. 1..how can this be with a controll circuit cut. 2. will I hurt anything if I connect the cut wire that went to the common of the pressure switch

 

[technoid]

the more I think I know about this gen the more I find out I don't. hope this makes sense to someone. reading a thread recently that talked about starting sequence to get oil pressure up before releasing the start position made me take a second look at the wiring to the oil pressure switch. there was only 1 wire attached and that was to the nc connection. found another wire that had been cut which I believe went to the c connection. this leaves the control circuit in the open position. testing the fault indicators shows all lights operable and system clear of faults. 1..how can this be with a controll circuit cut. 2. will I hurt anything if I connect the cut wire that went to the common of the pressure switch

Holding the start switch till OP comes up prevents the engine fault to trigger if the OP switch is closed. Check the cut wires of where they suppose to go by the TM drawing. Keeping the start held by passes the circuit that would fire K12 the engine fault relay. If your OP wires are in the wrong place your engine will remain in fault. I would study the TM drawing closely. Follow the numbered wires to the right terminal. That is the best way to know where wires go. You might have a bad OP switch and that is why the wire was cut. Some one was testing the switch

 

[Guyfang]

Try looking at the door of your gen set. There is the schematics on it. locate OP, the LOP, Low Oil Pressure switch. Notice that it has two wires connected to it. Wire #143C is connected to C and wire #126A connected to NO. The TM's are your friend.

 

[builmord]

Holding the start switch till OP comes up prevents the engine fault to trigger if the OP switch is closed. Check the cut wires of where they suppose to go by the TM drawing. Keeping the start held by passes the circuit that would fire K12 the engine fault relay. If your OP wires are in the wrong place your engine will remain in fault. I would study the TM drawing closely. Follow the numbered wires to the right terminal. That is the best way to know where wires go. You might have a bad OP switch and that is why the wire was cut. Some one was testing the switch
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[Guyfang]

You assume wrong. Why do you think that you have to hold the start switch up in the first place, other then to engage the starter? When S1 is held up, all engine saftys are bypassed. That meant for the oil pressure switch, that the oil pressure comes up. Then when the oil pressure is high enough to CLOSE the switch, you can safely let S1 go. The circuit is made. If you have a low oil situation, the circuit OPENS, telling the fault indicator to suhut down the engine and turn on the low oil pressure light. Just like described in post #2. Hook the wires up IAW the instructions and see what happens.

 

[builmord]

I did not hold the switch in the crank position, it was in the run position the same one that activates the fuel pumps. I will check again but I did not see any wire identification that was useful. what I can't understand is why the system shows no faults with the pressure switch disconnected form the circuit. unit runs fine but the low oil safeguard is not in play, not good. could someone have jumped out this circuit

 

[Guyfang]

I will check again but I did not see any wire identification that was useful. what I can't understand is why the system shows no faults with the pressure switch disconnected form the circuit. unit runs fine but the low oil safeguard is not in play, not good. could someone have jumped out this circuit

All wires are marked with wire numbers. find the right numbe, hook it to the right place.

Also, I made a mistake. Wire #126A is connected to NC!!

Its midnight here. My only excuse.

 

[builmord]

thanks, I will try again tomorrow to trace the wires. I still feel that given an open circuit as far as the oil pressure switch why doesn't a fault show up.

 

[DieselIron]

thanks, I will try again tomorrow to trace the wires. I still feel that given an open circuit as far as the oil pressure switch why doesn't a fault show up.

The LOP circuit allows the motor to run when it is open or disconnected. That's why it connects to N.C. and not the N.O. contact.
When the oil pressure comes up above 15 lbs. or so, the LOP switch opens. To test the fault circuit connect (short) the two wires going to the LOP and it should shut down the motor and signal low oil pressure.
I just had this problem on a newly acquired MEP-803A that had the wires cut to the LOP switch. Turned out to be a bad K20 relay that was not energizing.

 

[Guyfang]

The LOP circuit allows the motor to run when it is open or disconnected. That's why it connects to N.C. and not the N.O. contact.
When the oil pressure comes up above 15 lbs. or so, the LOP switch opens. To test the fault circuit connect (short) the two wires going to the LOP and it should shut down the motor and signal low oil pressure.
I just had this problem on a newly acquired MEP-803A that had the wires cut to the LOP switch. Turned out to be a bad K20 relay that was not energizing.

Correct. You can also jump from K16-8 to K20-8.

 

[builmord]

thank you. I will work as you directed.. just a question. can I do a check with out starting the engine and just putting the starting switch to the run /prime position and then shorting the 2 wires to see if the oil fault lite comes on and relay k20 energizes

 

[DieselIron]

thank you. I will work as you directed.. just a question. can I do a check with out starting the engine and just putting the starting switch to the run /prime position and then shorting the 2 wires to see if the oil fault lite comes on and relay k20 energizes

No, there is a lot going on in that circuit and with no oil pressure, the LOP switch is effectively shorted as it using the N.C. connection. You need the motor running. As long as your motor is making oil pressure as indicated on the OP indicator, you are not going to harm anything by running then testing the wires at the LOP switch. If you like you can unplug the wire to the N.C. post and reattach to the N.O. post temporarily to test LOP fault.

 

[builmord]

I traced wires from oil switch to terminal board p7 , #4 and 5 then to relay k16 #8 and k20 #8. shorting the wires does nothing, unit still runs and no faults are displayed. I wish I had a one line diagram to follow . it would help me understand how the system works

 

[DieselIron]

I traced wires from oil switch to terminal board p7 , #4 and 5 then to relay k16 #8 and k20 #8. shorting the wires does nothing, unit still runs and no faults are displayed. I wish I had a one line diagram to follow . it would help me understand how the system works

Check that K20 (Oil pressure fault relay) is engaging when starting up. You can view the internal relay arm moving when it starts up.
The MEP803 I worked on last did not engage. Had corroded contacts preventing K20 from energizing. If K20 is not engaged, it will not see the LOP fault.

 

[technoid]

You assume wrong. Why do you think that you have to hold the start switch up in the first place, other then to engage the starter? When S1 is held up, all engine saftys are bypassed. That meant for the oil pressure switch, that the oil pressure comes up. Then when the oil pressure is high enough to CLOSE the switch, you can safely let S1 go. The circuit is made. If you have a low oil situation, the circuit OPENS, telling the fault indicator to suhut down the engine and turn on the low oil pressure light. Just like described in post #2. Hook the wires up IAW the instructions and see what happens.

You did not read my whole post. Yes I know it bypasses all the safety when held. That's why we hold it so oil pressure is up before letting go. I worked on large commercial gensets that used timers on the oil fail shutdown where there is no one to hold a start switch.

 

[builmord]

Thanks, all. and yes there is no movement of the contact s in k20 when the unit starts and is running. can't today but when weather clears I will remove k20 and test it

 

[Guyfang]

Test K20 by the -24 TM. A quick way to test it is to see what other relay moves on start up, and swap them.

Check that K20 (Oil pressure fault relay) is engaging when starting up. You can view the internal relay arm moving when it starts up.
The MEP803 I worked on last did not engage. Had corroded contacts preventing K20 from energizing. If K20 is not engaged, it will not see the LOP fault.

View attachment 786793

 

[Guyfang]

Thanks, all. and yes there is no movement of the contact s in k20 when the unit starts and is running. can't today but when weather clears I will remove k20 and test it

Keep in mind, K20 may be working right. Before pulling the relay out, connect your multimeter to K2-A and B. set the meter for VDC. Start the set. Do you get 24 VDC? If not, then the problem is someplace else.

 

[Guyfang]

Testing the K20 relay. When not energized: Pins 7 & 4, 8 & 5 and 9 & 6 should be open. Pins 7 & 1, 8 & 2 and 9 & 3 should be closed. When the relay is energized: Pins 7 & 4, 8 & 5 and 9 & 6 should be closed. Pins 7 & 1, 8 & 2 and 9 & 3 should be open.

 

[Guyfang]

2-90.1. Testing the LOP.

a. Shut down generator set.

b. Open left side engine access door.

c. Tag and disconnect low oil pressure switch (1, FIGURE 2-25) electrical leads.

d Set multimeter for ohms and connect across switch connector pins C and NO. Multimeter shall indicate

open circuit.

e. Connect multimeter across switch connector pins C and NC. Multimeter shall indicate continuity.

f. Start generator set. Place BATTLE SHORT switch in ON position before releasing MASTER SWITCH

from START position.

g. Connect multimeter across switch connector pins C and NO. Multimeter shall indicate continuity

h. Shut down generator set. Return BATTLE SHORT switch to OFF position.

i.

j. Connect electrical leads remove tags and close left side engine access door.