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MG MGB Technical - The continuing fuel pump blues

OK, after help on this site from many of you, I broke down and got a rebuilt pump, and it runs on the bench connected to 12 volts. It also runs hanging from the wires under the car. It runs right before I slide it into the clamp. When I do that, it stops cycling. I can slide it in and out and it starts and stops each time. To rule out the wiring, I connected it to an external 12 volt source and it did the same thing, so it is either the pump or some kind of electrical interference. The clamp has not even been tightened when the problem occurs. How in the world can this be? I'm getting tired of looking at the bottom of my B...
Help!!??!!
michael

Forgot to mention that it is a '70 B. Also, pump runs in any orientation on the bench. And, I am using duct around the pump where the clamp attaches.
If anyone needs me I'll be under the right rear wheel well...
michael

Possible that there is a break in a wire that is only open when the wretched device is in its home position. Since you tried external 12v, it would be the ground, unless you had both hot and ground direct to the pump with the ext feed. Describe your hookup exactly, and measure voltages at the pump connections in situ. Depending on that, if there is 12V getting to whatever the FP is grounded to, and that point is NOT in fact grounded, you would have 12V+ on both sides.
FRM
http://www.usachoice.net/gofanu
FR Millmore

I don't know if it makes a difference (and it shouldn't with insulation) but the older MG's (not yours) were set up positive earth & you might have been sold a positive earth pump.
Of course it IS an SU fuel pump and may require an exorcism.
Peter

DO check the ground. The white wire above should check out as +12, and the green wire below should be grounded. The fuel pump ground wire goes back and grounds with the taillights, which means that if your taillights have a bad ground the engine will die. God Bless England. Anyway, try grounding the terminal on the underside of the pump (run an alligator clip from the pump, to a really solid ground such as those metal clip things that hold up the wiring loom) and see if the pump starts working.

Best of luck with it.
Sam

If you connected *both* wires from the external 12v source directly to the pump in order to eliminate your own wiring, which is the only thing that would make sense, then it has to be in the pump. It *could* be loose connections to the terminals inside the pump, but the chances of external and car wiring causing that to make and break under the same movement of the pump is pretty slim, I would have thought. I'd do it with the end cap removed and test for voltages each side of the solenoid and the contacts to try and determine just where the open-circuit (if that is what it is) is occuring. You have proved that when the pump stops pumping it isn't drawing any current, I presume? And how are you getting it to pump continuously? No fuel in the tank? Inlet pipe not connected? Outlet directed into a container?
Paul Hunt

Green car?
R. L Carleen

R. Carleen - Red car, but used to be green. Painted by PO. Where does this fit in?

Paul et al:
Definitely the pump, and I am exchanging now. Thanks everyone for the help.
michael

This thread was discussed between 22/05/2004 and 27/05/2004

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