MEP-804 not running

[MAdams]

I just bought this unit and it ran but made no voltage. I adjusted the mag pickup and moved the high/low voltage board to the low position. Now the engine will only stay running if the main switch is held in the start position. It runs great but once I let off switch the engine shuts off. The mag pickup has 750 ohms and I have adjusted AC voltage when using the dead crank switch to 2.7vac. I also bought a new mag pickup just in case but I have the same results.

The only other work I have done is move the board to the low voltage spot.

Any ideas?

 

[Guyfang]

Start the engine, Hold the start switch up to keep it running. Flip the emergency run switch up, to the emergency run position. What happens? Do you get any idiot lights (fault indicator lights)? Will the main AC light off?

 

[MAdams]

Ok I ran the unit today for about 5 min while holding the main switch in the start position. No idiot light with or with out the battle stich on. I tried closing and opening the contactor several times but only have about 25vac. Adjusting the freq knob does raise and lower the rpm slightly.

When measuring ohms on the freq pot knob with a dvom the ohms value jumps all over the place on the dvom. Any idea of the range of that pot?

 

[kloppk]

The Freq pot should be 5,000 ohms

 

[Guyfang]

Yesterday, I should have told you to let the start switch go after turning the emergency switch on. Not to hold the start switch up the whole time. The idiot light will not come on until the start switch is released. When you hold the start switch in the start position, it by passes all your engine safeties. If the problem is an engine safty problem, the engine should continue to run and an idiot light should come on. If the engine dies, then we need to look someplace else for the problem.

If you only have 25 volts AC, it sounds like to me you need to check the Quad circuit, and or check the volt regulator. Holding the start switch, (S-1) in the start position, sends excitation voltage, (24VDC) to your main AC to light it off. If the Main AC will not light off, you need to check your stator winding also. Do you have all the TM's for the MEP-804? TM 9-6115-643-24, page 2-64, Paragraph 2-33 give you the information needed to test the AC volt adjust rheostat. Lots of good info in the books!

 

[MAdams]

I do have the TM's and page 2-64 and on look like a good place to start. Both freq and volt pots are in spec. I still think the mag pickup is the problem but finding an exact replacement is difficult.

 

[Guyfang]

If you have 750 ohms on the mag pickup, then its good. Go to page 4-3, paragraph 4.2 and do the checks for the Governor testing. But I think you need to start simple. Why doesn't the set run by itself? Correct that problem and you will be able to look at the set without holding up the S-1. Did the set run with the S-7 turned on, and the S-1 released?

 

[tcruwithme]

Following. I recently bought an MEP-004A that has the same symptoms. I spent a couple hours reading the TMs today, and it looks like I need to replace a few relays.

 

[Guyfang]

Explain the symptoms. Everything it does, or not do.

 

[Guyfang]

Hey, MAdams, whats going on with you?

 

[MAdams]

Frustrated. I can only work on it during the weekend but I am out of ideas. I ordered a new Woodward governor and I am going to install it this weekend. My old HS auto shop teacher always said "Be a mechanic and not a parts changer" because so many guys would just guess at what was wrong instead of properly diagnosing the issue. I am now a parts changer. How much are plane tickets to CA from Germany? lol

 

[Guyfang]

Explain the symptoms. Everything it does, or not do. You may not need to go that route. Give me something to work with.

 

[MAdams]

Still the same thing. the engine will only stay running if the main switch is held in the start position. It runs great but once I let off switch the engine shuts off. The mag pickup has 750 ohms and I have adjusted AC voltage when using the dead crank switch to 2.7vac. This is with the battle short in both position.

 

[Guyfang]

All diesel engines have a fuel cut off solenoid. It cuts fuel off the fuel to the injector pump, to stop the engine. You need to see if the voltage is present at the solenoid during start, and if it drops off when you let the start switch go. If the voltage drops off, then you need to see why. You need to look at the schematic and see what path the voltage takes, and then find out what component is cutting off the voltage. Also keep in mind, the S-1 could be bad. Also try this. Start the set. Hold the start switch up. Press the fault indicator reset in, and hold it. Let go of S-1. Does it stop? Do you have any idiot lights?

 

[robertsears1]

Guyfang is right about newer diesels having a fuel shutoff that is electric. We have three tractors from '72-'77 that all have a knob you pull and hold to shut down. My Ford 555C backhoe has an electric shutoff and it got to where it would be hard to start or just shutdown while working. I thought I diagnosed the problem to the fuel injector pump and took it to a place for a test (or so I understood prior to any maintenance). Got a call a few days later that it was ready. I show up and he says it tested fine but that will be $600 since he rebuilt it anyway without my sayso. Not happy!

Sure enough, put it on and same thing. Then I started to think again and noticed the the ignition switch had gotten wiggly. Took it apart and found a disk of bakelite material in the back was not staying in position so I crimped the back of the switch and it worked like a champ except I swear it ran better before the IP was rebuilt. The switch was letting the fuel solenoid close since it needed juice to stay open.

I agree with Guyfang that a diesel in regards to just running is simple, if it starts but quits, it sounds like the fuel is getting cut off somehow.

Robert

 

[MAdams]

Update. Thanks to Guyfang helping out a different SS member on his generator, I found that when S1 is in the run position, terminal 3 isn't getting voltage. I jumped 24v to the terminal 3 wire coming off S1 and the engine started and ran in its own. Terminal 3 does get 24v while I the start position, hence why it runs if I hold S1 in start. I'll order a new switch and then address the no voltage issue. Guyfand, thank you for all the help.