MEP-802A cranks but immediately fails with a low oil pressure fault

[pclausen]

Hi guys,

I have a 802A that will crank no problem using the dead crank switch, but when I crank it from the main switch, after like 1 revolution or so, it immediately fails with a low oil pressure warning.

Things I have tried so far:

• Removed the oil pressure sending unit and verified that oil is pumped out during cranking
• I get continuity across the oil pressure switch when not cranking
• Low oil pressure relay (K20) ohms out ok on all 3 contacts and energizes during crank

Should the oil pressure switch be open or closed when pressure is present? I'm trying to decide if I should leave it open or short it together to see if one of those conditions allows the engine to crank from the main switch.

Thanks

 

[pclausen]

Never mind. I got it to run by opening up the pressure switch circuit. So open circuit = pressure and I verified that with my meter.

Doesn't make any power and none of the gauges are working except for the battery charging one. Still, getting the engine to at least fire and run is a good 1st step!

 

[pclausen]

I removed the control box to check the wiring and I'm already seeing a couple of issues that I need to address. The L1 and L3 wires are frayed against the chassis much like I have discovered on the other 3 units I have torn down already. Unlike those 3, the engine on this one turned over real easy by hand and fired right up once I bypassed the oil pressure switch.

As stated above, all the gauges are completely dead when the set is running except for the temp gauge which pegs in the negative direction. I wonder if someone got some wires reversed or something. I also noticed the one of the wires to the fuel solenoid was replaced and not run neatly in the harness like the old one, but just kinda slapped on and is about 2 feet too long. So I'll clean that up as well. At least I have plenty of spare units from which to rob parts as needed to help troubleshoot this unit.

Even with the top covers off, it sure is much quieter than my 003! It also starts within a few seconds. The 003 on the other hand is much simpler to work on.

 

[R Racing]

Did you try to excite the field ? Not sure how its done on the mep802a but on the mep002a you just turn the starter switch while running.

 

[zarathustra]

I've had a similar problem -- I found that the plug in switch S14 (crank disconnect switch) was installed backwards. There were a couple of vendors for that switch. One made it "murphy proof" so that it could only plug in the correct way, and the other vendor made his so that it could be installed 180 degrees out. If you remove the switch and look at the pins... if all the pins are in place you have the "murphy proof" switch. If it only has a few pins on it then it is the one that can be installed 180 out.

With the one I had a problem with I'd crank the engine with the master switch and get an oil pressure fault light. 'Found that the circuitry is rather convoluted to get from S14 to the oil pressure fault indicator, but it will track back if you want to take the time.

The gauges not working problem should be fairly easy to fix. With the exception of the DC Alternator gauge, all the "health gauges" get their power from the same place.

Not generating ANY electricity could mean something much more serious. Even with the voltage regulator disconnected it should generate enough electricity to deflect the Hz meter to 60. In my experience I've found that no electricity at all meant stator problems.

z

 

[pclausen]

Thanks for the advice! I'll check out these recommendations next time I have some time to work on it. When I checked it over before attempting to start it for the first time, I noticed that little 4 conductor harness plug under the control box was disconnected. That's probably a bad sign...

 

[zarathustra]

The four conductor plug/jack carries the 2 Quad wires and the 2 exciter wires.

Regarding S14 -- that has a relay socket, and the socket looks just like all the others. So, if someone has plugged a relay into that socket, that could be the source of your "oil pressure" problems.

What is supposed to be in there is a component that LOOKS like a relay, but instead has a circuit board inside with ~20 or so components on it. It would be very easy for someone to put a relay in its place since at first glance it looks like it is a relay..
z

 

[pclausen]

I wish it was just someone putting a relay in S14! However, the components all appear to be in the correct positions as seen here.


http://www.cstone.net/~dk/MEP802-11-14-02.JPG

Overall, the inside of the control box is pretty clean.


http://www.cstone.net/~dk/MEP802-11-14-03.JPG

Here's the front panel. As stated before, when running, the coolant temp goes all the way down and no other gauges move at all except for the charging indicator, which goes deep in the green.


http://www.cstone.net/~dk/MEP802-11-14-04.JPG

Here's the frayed wire under the control box (red arrow) and also the extra long fuel solenoid wire someone added (attached at yellow arrow).


http://www.cstone.net/~dk/MEP802-11-14-01.JPG