MEP 802A Aux Fuel Pump

[Guyfang]

There is strength in numbers! Add to that, having a smart book is always better then not having a smart book.

 

[Coley]

Howdy,
Nevermind. Going back and forth reading to many TM's
Here it is.

Set float switch stem 1/16 inch from bottom of fuel tank . Tighten switch plate adjusting nut. Connect electrical connector and remove tag. Install front housing panel, paragraph 2-18.4. Connect negative battery cable and close access door

Sorry, been away from computer. Thats the only guidance I have seen on that.

CF

 

[Coley]

So I am guessing that my issue is connected to my main fuel tank gauge not working. Will work that angle.

CF

 

[jamawieb]

Did anyone find an solution to this problem? I'm having a similar issue. I'm losing voltage after the float module, I can unplug the pump and I get 24 volts but as soon as I hook the pump up, it drops to 7 volts. So I changed the pump with a brand new one and still have the issue. Then I changed the module and float with a brand new one, still nothing. I can jump the terminals 1&2 on the J15 connector before the float module and the pump will start working. So it tells me that the issue is with the float module but I put a brand new one and it doesn't work

 

[Guyfang]

Has this set ever worked right? Or is a new one you are working on?

When you unplug J15, and mesure across pins 1 and 2, do you get any voltage?

 

[jamawieb]

Just obtained unit, so new to me. Apparently while in service with the military they had the same issue because they hard wired into the main pump. So while the main pump was on so was the aux pump. I changed the float module with 2 other modules which I know work and still the same effect. I can read 24volts at the aux pump plug with the pump disconnected. As soon as I connect the pump, it drops to 7 volts. I tried a brand new pump because I thought the pump was bad but same result, it dropped to 7volts again. I can jump the plug (J15) before the float module at terminals 1&2 and the pump will start working. I also changed out the float switch and still the same result.

 

[justacitizen]

just guessing. could there be a broken conductor inside one of the wires but the insulation is undamaged???

 

[Guyfang]

Now when I have good voltage, (24 volts) and I hook up a load, and the voltage breaks down, I would start looking for a ground problem. The problem with measuring voltage is that a loose connection, or pushed out pin, will pass voltage, but not amperage. So as soon as you hook up a load, (fuel pump) the voltage drops off.

Is the wire harnes hacked into, anyplace? Or hillbilly repaired? If I was going to hillbilly repair it, I would "fix" it at S1. As a matter of fact, if you have a bad connection on S1, that would do the trick. Check out if S1 is hooked up right. That where the voltage comes from on both fuel pumps, just two different pins.

 

[jamawieb]

Nothing is hacked and I checked all the connections in the schematic for the aux pump to make sure they are tight. The one weird thing is, that I can jump Pin 1&2 on J15 connector before the float module and the pump will start working. If I jump Pin 1&2 after the module, nothing. Ive tried 2 different modules (1 brand new and one from a working unit) with the same results.

 

[Guyfang]

Have you tried doing the same thing on a working unit?

 

[zarathustra]

The liquid level sensor (sort of a "Z" shaped piece with TWO rubber floats on it located near the front of the tank with four tiny wires coming out of it.) will shut the unit down when there is no fuel. That half of its job seems to be working. The liquid level sensor also has a second float on it that turns the aux pump on and off. When you said you checked the float I assume that you were checking the liquid level sensor, and not the float that connects to the fuel gauge. The fuel gauge float has no effect or connection to the aux pump. It doesn't do anything other than control the gauge.

It is possible that the liquid level sensor second float is not working properly. One way to check... if the 24 vdc is getting to the right spot you could measure the voltage at the liquid level sensor connector. That connector would be the first one y'all will run across when you trace the wires from the LLS. If you have 24 vdc you could short the two pins that would simulate "empty tank, turn aux pump on" to see if the pump comes on. I don't remember which pins on the liquid level connector are for the "turn pump on", but you can read them off the schematic. There are only four pins on that connector. That detail is not on the overall schematic, but on one of the detail wiring drawings. That detail drawing is in the back of the manual, but is in very tiny print. Y'all will have to enlarge it to read it on the screen. There are around seven or so of those wiring drawings... If you study it a little you'll find which drawing it is on. If I remember correctly it is one of the latter drawings.

The other thing that can go wrong with the liquid level sensor is that the second float is binding up a little and is not free to move.

As a last resort, you could remove the liquid level sensor and move the float down to simulate empty tank and see if the pump comes on. In the end that might be the easiest thing to do.

 

[jamawieb]

I have several NOS floats so I tried that first to make sure it was not the float. The floats job is to complete the circuit for the aux fuel pump; when the float for the aux fuel system is at the top it cuts the circuit to cutoff the pump. When the float falls, it makes continuity and starts the pump again. I believe the problem is with the float module because I can jump the connector (to make continuity) before the float module and the pump will start. If I jump the connector after the module nothing happens. I purchased a float module from Evil Dr. porkchop that he is parting out to see if it fixes it. I took one from one unit that I thought was working and now it doesn't work on either unit and I have a brand new one that is apparently defective also.

 

[Guyfang]

something fishy here. Let me know what happens when you get the new module. Try it in the known good set first!! I will then ask a friend if he has ever heard of such a thing. There my be some kind of problem in the set, causing the module to go bad. So try it in a known good first.

 

[jamawieb]

I had another unit like this years ago and I could never figure it out so I sold the generator to someone who was not interested in the aux fuel pump working.

 

[zarathustra]

If I understand you correctly you suspect the actual liquid level sensor?? If so, it is highly unlikely that several LLS are bad. So, if you suspect the LLS, I'd try to make sure that the float isn't binding somehow. Also. for the 2a (which I think is what you have) it is a definite "Z or J" shape, whilst the 3a is more like a sideways "N" shape. The floats are mounted a little differently on the 2a vs the 3a. Whilst the two LLS function the same, and kinda look alike, I don't think they are interchangeable.

If by module you mean the unit on the lower side of the unit, then I'd still suspect something weird rather than the unit itself. 3 bad modules in a row seems awfully unlikely. I've seen pins in plugs that have lost their retainer and the pin itself is shoved backwards. To make matters worse I've seen pins like that that still appear to stick out enough to make contact. I've seen wires broken internally that otherwise look just fine. Or perhaps just enough corrosion on either the male or female side of a plug as to not make contact (doesn't take too much).

Could be that some hammerhead miswired a pin somewhere...

This is the kind of problem in which you will learn more than you ever wanted to know about that circuitry.

 

[zarathustra]

OH, by the way, when you figure it out please post your solution.

 

[jamawieb]

If I understand you correctly you suspect the actual liquid level sensor?? If so, it is highly unlikely that several LLS are bad. So, if you suspect the LLS, I'd try to make sure that the float isn't binding somehow. Also. for the 2a (which I think is what you have) it is a definite "Z or J" shape, whilst the 3a is more like a sideways "N" shape. The floats are mounted a little differently on the 2a vs the 3a. Whilst the two LLS function the same, and kinda look alike, I don't think they are interchangeable.

If by module you mean the unit on the lower side of the unit, then I'd still suspect something weird rather than the unit itself. 3 bad modules in a row seems awfully unlikely. I've seen pins in plugs that have lost their retainer and the pin itself is shoved backwards. To make matters worse I've seen pins like that that still appear to stick out enough to make contact. I've seen wires broken internally that otherwise look just fine. Or perhaps just enough corrosion on either the male or female side of a plug as to not make contact (doesn't take too much).

Could be that some hammerhead miswired a pin somewhere...

This is the kind of problem in which you will learn more than you ever wanted to know about that circuitry.

Yes, I suspect the float switch module which is the box mounted to the right side. The power from S1 pin 5 comes into J15 pin 2 plug right before the module and then goes to P12 pin 2 which is the plug on the float itself. If you jump J15 Pin2 and Pin1 (before the module) it will activate the pump. But if you jump J12 Pin2 and Pin1 nothing. When you jump Pin 1&2 on J12 it should activate the pump but it doesn't, my voltage drops to 7.
This weekend I'm going to put the float switch module on and see what I get. I'll put it on the known good unit first to make sure it works, then put it on the defective unit. I'll let everyone know what I find.

 

[jamawieb]

Ok guys, so I put on the float switch module that I received from Evil Dr. porkchop and it fixed my problem. So the one on the unit was bad, then I put another from what I thought was a good unit which was bad and finally a brand new that was bad. When I have time, I'm going to check the resistors and board in the float switch module to see what failed in all 3.

 

[Guyfang]

Just because it's "new", dosnt mean it's good. That the worst thing that can happen to you. Get a new part that's bad. Drive you over the edge, it can. Good job!

 

[jgilman]

I have an 803 A and am trying to get the aux pump to run. The pump is getting 21 volts at the two pin connector which plugs into the aux pump. I bought a new float switch which has the low fuel cut off and aux pump float. I have texted externally (with the float switch module standing vertically) with an ohm meter. The low fuel float works, it does, (it shuts the generator down with a low fuel indication) and that the high low aux pump float works, it does., the generator stay running. I have also replaced the fuel pump (with a new one) and powered it externally with 24 volts, it runs fine. It seems the problem is that aux pump is not getting 24 volts, rather, only 21 volts. I suspect there is loose or corroded connection in the control panel. I have pulled all the relays, and tightened and checked all the connecting screws they seem to be ok. The fuel gauge works fine. I bought the generator used a couple of years ago all ok, except the aux pump won't run. Having read the earlier posts I am going to read the pin out voltages suggested before my post. I suppose it could be a bad relay, but which relay is it that controls the aux pump? I have read the tech manual read the schematics as best I can and its not clear which relay is involved. It could also be the rotary, 'stacked' which which control the prime, and aux prime. Maybe its a bad switch. BUT, i will go through the prior posts and see what the pin outs read. Another thing which I change the aux pump position from low to high the voltage to the aux pump changes slightly, from 21.5 volts to 20 volts when its not calling for the pump to run. Thanks !