804a will not crank from master switch

[BDenmark92]

I don't post in forums very often, sorry if the following information is jumbled

I am a heavy equipment mechanic that normally works on large machinery but a customer recommended me to a friend who just bought a couple of military generators, one of which is an
MEP-804a. I am tasked with making sure both units are ready to be shipped to the Bahamas. They need to be reliable and I wont be able to go there to fix any upcoming issues
This generator is powered by an Isuzu with a Zexel injection pump that appears to have a 2 wire fuel solenoid.
Has 46hrs on meter and sealed documentation showing it was in storage for a long time

Initially the generator started and ran just fine. I started and stopped the engine a dozen times as I checked various systems and verified the power output. I let the engine run for about 30 minutes then killed the engine as I inspected his other generator.

When I returned to this unit, It would not crank from the master switch. I have confirmed the following.
- Will crank from dead crank switch
- Dead crank switch is in Normal position
- DC circuit breaker is pressed in and does not trip
- All contacts on master switch work as they should
- Activating the battle short switch has no effect

When the master switch is in the start position, both the start relay and the crank disconnect relay are activated
The glow plug relay is also activated
Fuel solenoid and crank relay do not activate

I have found if I apply 24V to either #3 or #5 in the image below, the fuel solenoid will immediately activate and the engine will crank from the key switch. The engine will continue to run until I remove power.

Questions:
-Does any part of the run circuit need to be satisfied before the start circuit activates?
-What tells the crank disconnect relay to activate?

 

[Zed254]

Have you found the TM section? Several items for 804A here: https://www.steelsoldiers.com/forums/generator-and-electrical-tms.121/

Main TMs here: https://www.steelsoldiers.com/threads/all-the-tms-you-need-to-work-on-the-mep-804a.148936/

 

[155mm]

MEP-804A - intermittent cranking, no starting

Tested the MPU per the manual. when dead cranking, manual says look for 800-900 OHM at wire 147 & 148 I got 701ohm When dead cranking, manual says look for 2--3v at the same spot. I got 2.5v With mine being ground off a little, I'm going to put in a new one, its $20 and Ill know it should...

www.steelsoldiers.com

Read and test thru this thread

 

[BDenmark92]

Thank you everyone, I am now equipped with more knowledge of these generators and will post my findings after I return to the job

 

[mciikurzroot]

A bit of fill in, the crank selector switch you have discovered serves several purpose's foremost in NORMAL its just that, it allows normal cranking starting and operation, in dead crank its ONLY purpose is to simply turn the engine over with absolutely no intention that the engine actually start, no fuel or any other 'running' function/s should be expected.
You made mention of checking the fuel solenoid, its really a bit more complex that what you are possibly more used to seeing as a function of the fuel solenoid, in this application this engine operates in a SYNCHRONUS mode, that means this engine and near every diesel gen set is synchronus for this discussion, operating at a fixed speed under all operating circumstances, plus or minus a few RPM at 1800 rpm .. The significance of this is that at that speed the set makes a common FREQUENCY common within the US, inside the control cabinet you will also fine a selector switch allowing 50/60 selection..60 is what you want i think ? My "think" is the Bahamas might be 50hz im not sure. So i have drifted off the purpose of the solenoid, in this application it meters near exact fuel to the injection pump to maintain the 1500/1800 desired speed and/or required torque. So when operating normally the voltage you will see being applied can be 5vdc up to maybe 12 or so vdc, BUT not a constant 24vdc. The varying voltages you will measure will be a reflection of the demand the set see's and is satisfying by applying more or less actual fuel to the IP
If you try to measure these solenoid voltages with a DVM its not very likely to capture the actual voltage, with an analog meter the meter needle will typically just be drifting.. These voltages are insignificant, you just care the set is operating normally for your purposes..

Best and good luck. mac/mc

 

[BDenmark92]

A bit of fill in, the crank selector switch you have discovered serves several purpose's foremost in NORMAL its just that, it allows normal cranking starting and operation, in dead crank its ONLY purpose is to simply turn the engine over with absolutely no intention that the engine actually start, no fuel or any other 'running' function/s should be expected.
You made mention of checking the fuel solenoid, its really a bit more complex that what you are possibly more used to seeing as a function of the fuel solenoid, in this application this engine operates in a SYNCHRONUS mode, that means this engine and near every diesel gen set is synchronus for this discussion, operating at a fixed speed under all operating circumstances, plus or minus a few RPM at 1800 rpm .. The significance of this is that at that speed the set makes a common FREQUENCY common within the US, inside the control cabinet you will also fine a selector switch allowing 50/60 selection..60 is what you want i think ? My "think" is the Bahamas might be 50hz im not sure. So i have drifted off the purpose of the solenoid, in this application it meters near exact fuel to the injection pump to maintain the 1500/1800 desired speed and/or required torque. So when operating normally the voltage you will see being applied can be 5vdc up to maybe 12 or so vdc, BUT not a constant 24vdc. The varying voltages you will measure will be a reflection of the demand the set see's and is satisfying by applying more or less actual fuel to the IP
If you try to measure these solenoid voltages with a DVM its not very likely to capture the actual voltage, with an analog meter the meter needle will typically just be drifting.. These voltages are insignificant, you just care the set is operating normally for your purposes..

Best and good luck. mac/mc

I appreciate you clarifying that. I knew that wasn't the typical fuel solenoid I am accustomed to.

 

[BDenmark92]

Finally returned to the generator and found the issue. K21 relay that provides "Governor control power" to terminal #3 on A5 pictured above was bad. Swapped the relay and everything functions perfectly.