MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - fuel pump int elec connections

now that the weather has improved I am back at getting my 1972 B back on the road.I am repairing the fuel pump and my spare which have both quit working( whats new)anyway the condenser/capacitor is connected differently on both pumps ? my car is neg ground. Which terminals should the capacitor be connected to?
B R pasmore

Originally a capacitor, on later pumps it was a diode. I believe the norm was to have the capacitor connected across the points so that it 'absorbs' much of the electrical energy that causes the spark and in that way suppresses it, just as in a distributor. In other fields it has been more usual to connect a diode across the component that generates the high EMF that causes the spark, i.e. the coil or winding, so that may explain the difference if you have both types. Polarity doesn't change this, although unlike a capacitor a diode *is* polarity concious and so must be connected the right way round, i.e opposing the normal current flow in the circuit. Connected the wrong way round the diode will probably be destroyed, and until it is the excessive current will be frying the wiring.
Paul Hunt 2

Some capacitors, namely electrolytic, are polarity sensitive, and explode if connected the wrong way. When I say explode, one the size of whats on the fuel pump would just pop but they get damn hot before they do that. I dont know if the capacitor on the fuel pumps are electrolytic, but its worth just being careful. If it is polarity sensitive it will be labelled with a + and -.
Ross Kelly

Capacitors used on the SU fuel pumps are not electrolytic although some of them look like they are. The capacitor is normally connected across the points. Later pumps used a diode/resistor assembly , which is attached across the coil as Paul stated. Either capacitor or diode/resistor will work to suppress arcing when connected either way. Cheers - Dave
David DuBois

This thread was discussed between 27/04/2008 and 30/04/2008

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.