MEP 002 blowing DC breaker

461
5
18
Location
Sandyston, NJ
What does the little electrical box with one wire coming into it and one going out to the fuel pump do? It is mounted just bellow the throttle cable. With it plugged in it blows the breaker as soon as I turn it to prime/run. With it unplugged the fuel pump works and breaker stays set. Also with that plug unplugged and I turn to start it trips the breaker right away. I am not really good at tracing wires and would like any help or ideas to what could cause these problems.

Thanks
 

RichardR

Member
96
3
8
Location
Austin, TX
That little box in the DC power line to the fuel pump is an electrical filter to reduce any radio frequency interference generated by the fuel pump. It is failure prone, as you have found out. The most common failure mode is for a capacitor inside the box to short out and ground the DC power line to the fuel pump. The most common cause is a spike on the DC power caused by, for instance, a loose connection to the battery or manually removing the battery cable while running.

It's practically impossible to repair since the box is soldered shut and all the internal components are embedded in hard potting compound. I don't know if a replacement filter box is available from Facet (the manufacturer) or elsewhere.

The only practical solution is to cut the wires on either side of the box and rejoin the wires, eliminating the box from the circuit. That will at least make the fuel pump work again. I haven't heard that anyone has had problems with whatever radio frequency interference may be unleashed by this solution.

Hope this helps,
Richard

P.S. Another solution, of course, is to replace the entire fuel pump and filter box assembly. They are available from Facet fuel pump distributors for about $200, and sometimes (rarely) less on that auction site.
 
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There are two pumps in series. It only takes one running to get fuel to the Injector Pump (IP). You are probably hearing the second pump running.

You also stated "Also with that plug unplugged and I turn to start it trips the breaker right away..." Are you saying that you can not start the engine? meaning it won't turn over when you go to start because the CB pops? :?:
 

Speddmon

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Cut the wire from the "box" at the fuel pump and remove it. The fuel pump will work fine without it. You already know that is the problem, and that should solve it.
 

RichardR

Member
96
3
8
Location
Austin, TX
The only practical solution is to cut the wires on either side of the box and rejoin the wires, eliminating the box from the circuit..
What I meant to say was, "...cut the wires on BOTH sides of the box and rejoin the wires, eliminating the box from the circuit." In other words, disconnect the box completely from the DC power line to the pump. As others have noted, there are 3 pumps altogether, and it is sometimes hard to tell which are running and which are not.
 
461
5
18
Location
Sandyston, NJ
Wildchild467- CB is referring to the DC circuit breaker on the control panel. The box we are talking about eliminating is mounted below and to the right of the throttle cable. From my understanding it is a noise filter.

Richardr- Thanks I will bypass that box. That solves one problem now just to figure out why it pops the CB in start. It does it even when that box and pump are disconnected.

Speddmon- I got that disconnecting the box will solve one problem. My other problem of popping the CB is when I turn to start with that pump disconnected it pops the breaker immediately.
 

Speddmon

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Speddmon- I got that disconnecting the box will solve one problem. My other problem of popping the CB is when I turn to start with that pump disconnected it pops the breaker immediately.

My bad, I missed that part of your problem. I would suggest disconnecting the starter solenoid and isolating the wires. I looked at the diagrams, and I would be willing to bet that there is something in that area wrong. That is one of the only things in the DC circuitry that comes in only when you are trying to start the machine.

If that is not it, you could have a problem with the bridge board, but that is a less likely scenario.
 

Grega

Member
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St. Paul Nebraska.
Disconnect the start wire on the starter and try to start again. You may have a starter solenoid problem. These tend get moisture inside and corrode.
 
461
5
18
Location
Sandyston, NJ
Ok so I disconnected the start wire from the solenoid. It is still popping the breaker. Now I noticed this just now with the wire connected or disconnected and I turn the master switch half way between prime/run and start I here a relay or solenoid click behind the control panel. Only when I turn the switch all the way does it pop the breaker. Not sure if this info will help but that's all I have for now.
 
461
5
18
Location
Sandyston, NJ
Well I have been making progress. I am at he point now where it will start and then shut off right away. The only way i can get this to happen is either with the temp sensor or the oil sensor disconnected. With that circuit connected it still shorts and pops the breaker. I have also bypassed the noise filter on the pump and that is no longer a problem. The oil sensor is new. Any help as to where I might find this short now will be great.
 

Speddmon

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You may have an issue with the wiring harness or possibly a grounded switch. Start off by metering the high temp switch to ground. Use the meter and check each pin of the connector where it goes INTO the air box to ground. You should have no continuity to ground on those two pins. If they check good, do the same thing with the oil pressure switch. If they check good, very carefully and thoroughly go over the wires to and from each switch and look for insulation rubbed through or a wire burned.
 
461
5
18
Location
Sandyston, NJ
Ok I disconnected the switches (oil and temp) Pinned out to ground. The temp switch does not go to ground but with both leads disconnected on the oil switch and pinning the switch out to ground I get ground on one of the terminals. I bypassed the temp and oil switch by wiring the wires together and I still get a start up and immediate shut down.
 

storeman

Well-known member
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Location
Mathews County, VA
You have done what I suggested in pm. I'm not electrically smart enough beyond that point, other than to suggest that you check to see that you actually have a good ground strap and solid connection from engine to the frame and a good one from control box to frame.
Jerry :grd:
 

Speddmon

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One problem at a time. Replace the oil pressure switch and see if you get the breaker issue figured out.

After you do that, start it again and (you may need a soldier "B" for this). While you are starting it, gently hold up on the fuel shut-off solenoid. It should stay running while you hold up on the solenoid. Keep a close eye on the oil pressure. If it stays running that is good. We'll figure the rest out soon enough. You could have an issue with the solenoid, or the master switch or the K1 relay.
 

couchilla

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atlanta ga
MidnightDuramax did you ever get this one to run? I'm having some similar problems and would like to know if you got it figured out. Thanks
 
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