Working on an SW9. The fuel pump was intermittently slowing and shutting off. I had another motor that I installed for the time being, but here are the questions.

Who rebuilds 74vdc motors?

What should the fuel pressure be on a SW9? With the old motor it would run 12-15psi (when it worked). With the new motor (same pump) it runs at 40psi. Both the operators manual and my engine maintenance manual are not clear on this. One says 5psi minimum and the other just talks about the various pressures of the bypass valves. With the new motor, and higher pressure, I now have a small amount of fuel "percolating" through the bypass sight glass where it never did before. Filters are clean.

Thanks in advance
E

In my infinite wisdom, I'd say it sounds like you got it working right. To be sure, or for a recommendation or rebuild of your old motor (maybe an exchange), you should try McHugh Locomotive & Equipment (215) 949 0430 www.mchughlocomotive.com Best of luck to you.

Any good electric motor shop should be able to rebuild that fuel pump motor. I have one here in Indiana that has done some for me. Mine did not need a total rebuild. One was too bad to rebuild. Diesel fuel had leaked in to the motor and destroyed the armature.

Before sending it to someone for a unit exchange, unless you have dealt with them before, I would have a local shop look at it. You could even pull it apart and see what the insides look like.

EMD fuel pumps typically come in three or seven gallon per minute capacity. On Conrail we got rid of all the three gallon pumps because they would inadvertently be installed on 16 or 20 cylinder road units which resulted in fuel starvation. It was not unusual for the higher capacity pumps to bypass fuel on 8 or 12 cylinder units at idle.

When the AC pumps came along they were capable of much higher output pressures which frequently resulted in the bypass or primary sight glasses rupturing. The cure was to remove the 60 psi relief valve and put a short 1/4” nipple in its place to act as a standpipe.

One thing to keep in mind if you have fuel bypassing and poor performance that you can’t pin down is to look and see if your fuel pre-heater is leaking and water is emulsifying the fuel and clogging the injector internal filters. If you pull one and it’s loaded with brown goo then you know the deal.

And one more once in a million deal is I once had a unit where the fuel pump was actually rotating backwards creating enough pressure to rupture the primary glass. We flashed the aux gen and after the fireworks everything returned to normal.

EBL

IIRC the fuel pump motors are brushed motors. Usually when they get intermittent and slow, the brushes are worn. Near the tail there should be a pair of screwed in caps, the brushes (carbon blocks with a braided wire) will be under there.

I think I found a local shop to check the motor. I had already checked and cleaned the brushes. The comutator looks questionable. The one brush is adjustable (like old non regulated generators) and I would like to find some info on how to properly adjust them.

See attached EMD MI specs. The A-731 is the Fuel Pump motor. I have the entire MI, but it's too big to upload without splitting it into separate smaller PDFs. There is not real procedure outlined for brush adjustment. Hopefully this helps.

- Walker