MEP-831a Troubleshooting

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DieselAddict

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I picked up the generator from GL at Fort Bragg today. Physically it looks to be in great shape. All the parts were there.

I put a splash of fuel in it and filled the crankcase with oil. It has great compression. The battery was totally flat. I decided to do a "manual" start so I put some fuel in the supply line and gave it a few yanks. It took some effort but it did fire up and run for a few seconds. It wouldn't stay running because there was no DC power on the control panel so once the fuel in the line was gone that was it. I was relieved there didn't seem to be an engine problem.

Let the troubleshooting begin. I parked it next to the MEP-003a so I could jump 24v to the battery leads. A quick look at the schematic and I started measuring voltages. On the inside of the control panel I checked TP30 (TB3-1) and had 15v. It should have been full battery voltage. I checked the AUX DC input connector on the side and had the correct battery voltage so that let me know the power from the input cables was making it OK. I unplugged the bulkhead connector (J7) and checked pin 17 of and had good BATT on the female side. I cut all the wire ties off the harness in the control panel so I could get a better look at everything on that side. A bit of wiggling the wires on the back of J7 flickered the voltage on TP30 so it looks like the bulkhead connector needs some work. I'm going to pull it out tomorrow and give it a good look. None of the pins are burned. I suspect its not fully seating.

Just to get things going I decided to jumper B+ across the connector. I put a jumper in place from the B+ lead to TP-30 and connected the jumper cables from the MEP-003a to the BATT cables on the 831. I clicked the main switch to RUN and we had control power. The fuel pump started up. Once the fuel system was fully primed I did a manual start and it fired right up and ran. It didn't run well but it did run. The speed control was TOTALLY out of whack with severe hunting but I was relieved it was running. I locked out the speed control and let the engine run against the mechanical governor for a bit to make sure it was sound and it ran perfectly.

Electrically it makes good power voltage and freq wise but I did have some intermittent cutouts of the AC from the inverter. It looks like the AC feedback from the inverter to the speed controller is also flaky. I could wiggle the wires on the back of J7 and see the voltage cutout relay go nuts. All of that should be resolved tomorrow when I pull J7 out and fix it. After I have the connection problems fixed I'll go through the procedures to set the speed controller up.

Someone at the maintenance depot tried to fix it but I think they gave up pretty quickly. Almost nothing inside was disturbed. It looks like they were concentrating on the mechanical speed control which was certainly acting up but it was due to the poor connections in J7.

So to summarize the unit is in great shape. It looks like its malfunction it is going to be straight forward to correct. I'll grab some images tomorrow while I work through the fix.

I paid more for it that I budgeted but if it really has under 100hrs on it I should be good to go for a very long time.
 

DieselAddict

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It looks like that one on ebay is the one that goes around the engine. I would need to replace the one in the control panel (if I can't fix the connector).
 

Dewie38

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What you have to lookout for is the engine may not have only 100 hours on it.
Some of these sets were reset at Letter Kenney and are not what they seem.
If you get into trouble let me know I have several of these units and parts.
I've been working on these sets for almost 20 years, great sets.
I'm the guy who troubleshoots these for the government.
 

DieselAddict

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Positive ID of the problem, the B+ lead in J7 is bad on the back of the bulkhead plug. Now to source a replacement and extract a bunch of pins.
 

Dewie38

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If you're pretty sure it's the B+ in J7, then that would be pin #17
You only have to extract that one pin, need Amp extraction tool #305183 and replace pin with Amp #66098-9.
Should be able to get at Newark electronics but you will also need crimping tool for that pin.
But could just try to squeeze the barrel of the pin with a pair of pliers to make better contact with the wire inside the pin.
 

DieselAddict

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The wire was broken off the back of the pin so I have to replace it for sure. I ordered the extraction tool and the connector. A bit of arcing happened and did some damage to the connector. I don't think I'll be able to get that pin out so it looks like I'll be taking the other 36 out and moving them to a new connector.

That is correct that its pin 17 in J7.

I am going to see if I can find someone around with the crimper. I don't want to pay $400 for a tool I won't use.

The pins I ordered was the #66361-4. That looked to be the right size for the wire. Do you think they will work?
 

Dewie38

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I checked Amp's website and I cant come up with that number.
Where did you order it from?
The connector is Amp #206151-1 cross reference which pins go into that connector.
 

DieselAddict

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Thanks for checking on that. Here are the components I ordered. The pins were the ones that were flagged to go with the connector.

Bulkhead connector - AMP 206151-1
http://www.digikey.com/product-sear...rcular-connectors-housings/1442557?k=A1307-ND

Pins - AMP 66361-4
http://www.digikey.com/product-detail/en/66361-4/A1650-ND/241439

On a happy note I checked all the other connections in the plug and found no other problems. I have the unit running the house now as I type this. I even tested if it could start my well pump and it started it without any issue.

A couple other items of note, the voltage adjustment pot had been replaced and wired backwards. I'll have to correct that. The fuel gauge is stuck on "E". It does move from full left deflection up to "E" when the engine starts but that's it. I'm going to check and see if its the sending unit or the gauge.
 

DieselAddict

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You only have to extract that one pin, need Amp extraction tool #305183 and replace pin with Amp #66098-9.
I found all the part numbers in a catalog and it looks like it I will be fine with either part number for the pins. The ones I ordered went down to 14 gauge wire where the number you have goes down to 16 gauge. The rest of the specs are the same.
 

Dewie38

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Yes sometime the wire gages overlap and that's the only difference in the pins.
Sounds like you have a bad fuel sender.
Have run my house with mine, you have to watch what you put on but it does it.
Very clean power I have never seen a cleaner sine wave on a genset.
 

DieselAddict

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Very nice. I have several friends asking me if I decided to keep it or not. :)

The connector parts will be here on Saturday. I'll get that switched out next week.

Dewie, If the fuel sender turns out to be bad what are your thoughts on where to get one?
 

DieselAddict

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The photos on the auction are helpful. Looks like its a pretty simple sensor. I may pull the old one out and see if its a simple fix.
 

Dewie38

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Not easy to remove from the tank because the float is offset.
The resistor is not sealed it's exposed in the tank and sometime the resistor gets messed up.
If you remove it place an ohm meter across the center terminal and the mounting flange and you should get 0 ohms down (tank empty) and 31 ohms up (tank full).
 

Dewie38

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If I were you I would just remove the sender and get a new one.
Mess with the old one later, It sounds to me with the J7 connector you have bigger fish to fry. I believe if you short out the sender wire to ground it should read empty.
 
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