MEP-004A --need help with no-start & fault light issues

This is a running unit that hasn't been started in about 8 months. Hooked up hot batteries, primed fuel system & then went to light-off & got no starter action, only fuel pump running. Starter is known good but I will be doing a "hammer-encouragement action" on the solenoid in a short while. Another problem is that the oil fault light doesn't work when start-run-stop switch is is in run position. Swapped out the oil switch with a known-good one & light does not come on like it should prior to start-up. I'm more comfortable with the starter diagnosis than the fault light issue. Thanks.

Edit--just verified no voltage to starter solenoid connection & also checked start/run/stop switch. Start/run/stop switch terminals all checked out properly.

Now looking into the special relay assembly to locate the start relay & will check if voltage is getting to the relay. I see three relays arranged vertically on the engine side of the box & now trying to ID each one.

Does anyone know if the relays inside the control cubicle are interchangeable with the relays inside the special relay assembly box? If they were I could do swap-outs for testing purposes.

Edit #2: The K3 (crank relay) is further inboard inside the circuit board that holds K5 (field flash), K8 (fuel level) & K7 (not found on FO-3 DC Schematic but found on FO-4 [AC Schematic] for parallel lights voltage sensor relay). I found one terminal has 24v when the start/run/stop switch is set to run position, but when the S/R/S is set to start, I found no 24v "signal" on either of the smaller wire connections. I also checked diode CR3 and found it had no voltage on either side with S/R/S switch in start position. Using an ohmmeter (with DC breaker pulled) the diode showed continuity with the leads connected one way and when the leads were reversed, no continuity was observed.

So at this point I know that something is preventing 24v to trigger the K3 relay to send current to the starter solenoid but I haven't figured out what that could be. I did connect a jumper across the 2 larger terminals on the K3 relay (one has 24v whenever the S/R/S switch is in the run position) and the relay will then send current to the starter solenoid & the starter will engage & spin the engine. My current theory is that since the K3 relay is not getting the 24v "signal" from the S/R/S switch & that it functions when jumpered, it appears to be good. I just haven't sorted out the schematic well enough to see where the problem might be. If any of you are have any ideas I would be glad to listen!

Thanks

If you have a small power supply you could probably bench test the relays they usually have a mini schematic on the side of the relay with pin out.

if the batteries are reversed, it will not crank. just sayin'

m-35tom said:

if the batteries are reversed, it will not crank. just sayin'

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Very true and the pump will still pump. Also is there a safety curcuit that would keep k3 from getting power?

Fuel pump runs? Check the battle short switch...

R Racing said:

Very true and the pump will still pump. Also is there a safety curcuit that would keep k3 from getting power?

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most units have a diode so it won't crank. that way it will never start and turn on the dc circuits that would be damaged.

Batteries are installed correctly. Thanks.

Edit--looked at wiring schematics & I see that a cable in the speed switch wiring harness seems to "feed" the voltage to the CR3 diode & K3 relay. I'll check the wiring in that harness & clean pins & sockets on the connector assemble & check reset button in a few minutes...

Update with good news! Cleaned pins & sockets on speed switch connector assembly, re-installed & also pushed reset button (couldn't really tell if the button felt any different after the reset). Unit bumped over when using S/R/S switch in start position. Now have to reassemble open boxes & verify everything is tight before actual start-up...then onto the oil light issue--hoping the oil pressure switch is the problem there.

if there is an issue with the oil fault light it likely will not crank. light must be on first.

Actually, I've cranked & run this one several times with the oil fault light not working. (Oil pressure is good when running.) The oil bulb works in test mode but does not light up when the S/R/S switch is in run position.

Yesterday I mistakenly changed out the oil gauge sender thinking it was the low oil pressure switch. Will make the correct swap-out this afternoon. Hoping that may be the problem. Thanks.

Update with solution. Something was bad on the fault indicator board. Relay checked out good but one of the resistors is bad but I didn't go any deeper for now. Swapped out the fault assembly with a known-good replacement and low oil light now functions properly. Never did swap out the oil switch so existing part was not the problem.

Sorry to drag up an old thread but found this to be super helpful and wanted to add my experience to hopefully help others in the future with similar issues. 1800 Diesel thank you for doing a lot of the tracking down on the starting circuit I found the TM to be pretty much useless in helping me with this issue. Pretty much I had the same exact problem you did with my 005a. It started out as I would have to hit the start switch several times and then it would go. I figured it was the solenoid on the starter just did not get around to dealing with it. Then went out to try and start it and noticed at all. Starter turned out to be fine like you and K3 relay was good like you and CR3 relay was good like you. Well turned out to be a failed microswitch inside the speed switch that was preventing mine from cranking. I documented my tear down and repair in the following thread for anyone interested. https://www.steelsoldiers.com/showt...ir-(mechanical-version)&p=2174010#post2174010

Thanks again for a great initial post and follow up, it is what led me to investigate the speed switch I was stumped.

Lee

leedawg said:

Sorry to drag up an old thread but found this to be super helpful and wanted to add my experience to hopefully help others in the future with similar issues. 1800 Diesel thank you for doing a lot of the tracking down on the starting circuit I found the TM to be pretty much useless in helping me with this issue. Pretty much I had the same exact problem you did with my 005a. It started out as I would have to hit the start switch several times and then it would go. I figured it was the solenoid on the starter just did not get around to dealing with it. Then went out to try and start it and noticed at all. Starter turned out to be fine like you and K3 relay was good like you and CR3 relay was good like you. Well turned out to be a failed microswitch inside the speed switch that was preventing mine from cranking. I documented my tear down and repair in the following thread for anyone interested. https://www.steelsoldiers.com/showt...ir-(mechanical-version)&p=2174010#post2174010

Thanks again for a great initial post and follow up, it is what led me to investigate the speed switch I was stumped.

Lee

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A quick way to check the Speed Switch, (S9 switch) when this is suspect, is to disconnect the C-Plug, and insert a paper clip in pins A&B of the plug. That's the S9-1 contacts. The S9-1 function is to cut out the starter when the engine hits the proper RPM. It ALSO keeps you from restarting the gen set when you have had an Overspeed shutdown. When ever I have a start problem with a 004, 005 or MEP-006, that's the first thing I check, because it's easy.

The mechanical switch is rare today. It went out of production long ago. I liked it because it was adjustable, AND repairable. You have to be careful when you order S9's, because not all of them fit every set. But they look about the same.