MEP002a - what's not quite right?

[Hectorsosa]

I've got an MEP002a that won't initially stay running if it's been sitting for more than a couple weeks. I thought I had it figured out when I spotted the wires arcing at the ground connection near the NATO plug. Cleaned up, reassembled and no arcing now, but no guaranteed run once the start switch is released.

Yes I know, there's multiple threads here that discuss the safety circuit. What I couldn't find is this - is the overheat sensor normally open or normally closed? I know the oil pressure switch closes on pressure, but I couldn't find details on the overheat. I'm assuming it's a dodgy oil pressure switch, but if I'm gonna dig in to it I want to check both. Thanks

 

[Mr4btTahoe]

You must hold the start switch in the start position until oil pressure builds. The starter has a switch that disengages the starter motor once a certain RPM is reached... but holding the main start switch in the start position bypasses the oil pressure and other safety switches.

Are you doing that?

 

[Hectorsosa]

I am. It used to take maybe 15 seconds for enough pressure to build, now it's taking 60 seconds or more. Not low on oil, and dial gauge shows pressure right away

 

[Guyfang]

Take a wire and hook it up on TB 5-8. run the other wire end to TB5-9. Try and start the set. Will it start and run? If so, the S4 or S5 is bad. As you can see, both switches are openers. To test S5, take off your jumper wire and connect it to S5-1 and S5-2. Start the set. If it starts and runs, S5 is bad. To test S4, the same. simply jump it.

 

[Hectorsosa]

So... overheat normally closed. Thanks

 

[Ray70]

Correct. Oil pressure and temp are in series and hold the Fuel solenoid open when both are closed. If either switch opens, the solenoid releases and shuts down the Injection pump. The temp switch is notorious for failing at any moment.

 

[Chainbreaker]

Last summer I had one of my -002a's shutting down only after unit got hot. That led me to think it was temperature switch which I swapped out with a new one I had on hand & problem still persisted randomly. It then progressed to not allowing unit to run immediately after letting go of start switch. Turns out it was oil pressure switch.

When looking for either the oil pressure switch or temp switch it pays to shop around. They can both be found fairly economically if you use the right part numbers, don't have them in front of me but I used the NSN # (-24P manual) to cross over to OEM #'s that meet spec's. A while ago I found the temp switch online at some lawn mower shop & the oil pressure switch (new style) can usually be found at your local auto parts store & online. It's good to keep a spare set on hand as it's a quick fix when you need them.