No power to MEP-802A main fuel pump

[gen508]

I had the engine running for a solid hour, generating power. The next day, no power to the main fuel pump when I turn the master switch to prime. I confirmed there is no power going to the pump when the switch is on run/prime. I also checked the diode CR1 as another member suggested, but it appears to be fine. Does anyone have any suggestions or experience with this problem?

 

[jamawieb]

I'm sure you already checked the emergency shutoff is not pushed in and also make sure the dc breaker is not thrown.

 

[gen508]

The emergency stop was not pushed and the DC breaker is OK. It fired right up the day it came from GL. It was frustrating that it stopped working one day later. As a quick fix, I suppose I could hot wire the fuel pump while I troubleshoot.

 

[jamawieb]

Have you tried switching the battle short switch on to bypass any safety switch. Also make sure your low fuel warning light is not on. If there is not enough diesel in the tank, the warning light will be on and the fuel pumps will not work (even with the battle short on). I had one that had a bad fuel gauge that showed full but I couldn't figure out why the light was on and the pumps would not work. I finally decided to put diesel in and everything worked perfect and the fuel gauge finally started working after a while.

 

[gen508]

I checked the low fuel shutoff functionality, it lit up and shut down the engine when the system worked. I'll give the battle short a try and top off the tank. It is odd that the engine cranks with the main switch, but will not prime. I think the next steps will be to check the master switch for continuity in the prime position, then start tracing the power lines to the fuel pump.

 

[DieselAddict]

Have you gone through the panel and tugged on all the wiring connections? It could be as simple as a loose terminal or a broken wire under a crimp connector. Those kind of problems are ones that are most likely and should be worked through first (in my opinion). I always look for mechanical connection problems on equipment that moves and shakes before moving on to other things. It should take less than 5 minutes to do.

Edit - It doesn't hurt to go in with a screwdriver and make sure all the electrical terminals are snug. Disconnect all power sources first.

If that isn't the problem, download this manual - http://greenmountaingenerators.com/wp-content/uploads/2012/10/MEP-802A-TM9-6115-641-24.pdf

Print page 107 (diagnostic port pin-out). Look at the wiring diagram (pg 279) and use the labeled test points (triangles with letters in them) to trace the voltage through the power circuit to the fuel pump (E2 on the drawing). The test point labels correspond to the pins on the diagnostics port. With the main switch in the RUN (not AUX RUN) position see if you have DC power between pins "K" and "D".

Once you do that you should start understanding the documentation and be able to look at the drawings to trace the circuit to find the problem.

 

[gen508]

Thanks DieselAddict, the diagnostics and schematics information was very useful. There are only 2 millivolts between D and K in the diagnostics port. I will go through all the connections with a fine tooth comb. Would the fact the circuit was not completely open at 0V make you suspect it is a diode?

 

[DieselAddict]

It could. Its worth a check. Since they are easy to get to I would say to go ahead and check them first.

The thing I would do next is to look at the schematic and follow the circuit back to the next test point. Check again and see if you have the expected voltage. When you find the first test point with the expected voltage you know the problem is between that point and the previous test point back. That will help narrow the search a lot.

 

[DieselAddict]

I should have mentioned this first.. Don't forget to test the diagnostic plug itself. Make sure you have good voltages across pins representing circuits you know work (like main B+ and GROUND). You want to make sure the ground and main power points in the plug are good since those are references for other test points.

 

[gen508]

I have a good 24V in most of the diagnostic ports except the circuit interrupter coil (V), which looks closely related to the fuel pump in the electrical schematic. Do you know where exactly the CR5 diode is located?

 

[DieselAddict]

All the diodes should be behind the instrument panel in the control box. I'll have go out and look at one to see if one is labeled CR5.

 

[DieselAddict]

I doubt CR5 is the problem. Its there to contain the inductive kickback from the fuel solenoid (L5). If it was shorted it would pop a fuse when the switch was thrown. If its open it will cause arcing on relay contacts along that same circuit during shutdown..

That being said, CR5 could be bad and you are now seeing the secondary damage from the arcing of relay contacts. My money at this point is that you have a bad relay.

 

[DieselAddict]

Make sure you have voltage on terminal 3 of the main switch. That is where the power that runs the pump originates. If you have power there then the most likely cause is the contacts of K12.

 

[DieselAddict]

Troubleshooting for the relay is on page 104 of TM9-6115-641-24.

 

[DieselAddict]

Also verified that CR5 is between terminals 10 and 11 of TB4.

 

[gen508]

All the relays tested good. There is power at terminal 3 of the master switch when I checked it through the diagnostic port. I checked diode cr3 and the AC circuit interrupter switch, both good. What doesn't appear good it the time meter. I could not get 24V to the time meter. Given where that meter is in relation to the fuel pump, could that be the problem? Would shorting the terminals of the time meter effectively bypass it?

 

[DieselAddict]

I think we are back to a broken wire or loose terminal somewhere.

Shorting across the timer won't help. It will just short out that circuit. Not exactly a problem since there is no power there.

 

[gen508]

Problem solved. In case this helps anyone else, there was a metal shunt / clip that connects posts 1 and 2 of Terminal Block 5 that came out while I was trouble shooting the coolant gauge. I had already pried the top cover off and spent a fair amount of time troubleshooting before I found the wayward clip. Thanks for the assistance. This is my first MEP and so far it has been an enjoyable success.

 

[DieselAddict]

Excellent. Glad to see you figured it out.

Mechanical connections... They will get ya!