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MG MGB Technical - It's got me puzzled again!

I have a strange problem with my GT so I was wondering if any of you guys had any ideas.

I upgraded my electrical system from the original dynamo spec four years ago, and use a Lucas 16ACR alternator. The problem I have is the power of the electrical system under load. I have a Kenlowe electric fan fitted and have replaced the original fuel pump to a Facet competition pump.

I have noticed recently that when the fan cuts in my fuel pump stops working, and when the fan cuts out the fuel pump starts working again. However, this does not happen all of the time, sometimes the fuel pump does not start working when the fan cuts out. When the fan is on I've given the pump a gentle (ish) tap and it starts working again. The pump is only a year old and the live and earth connections seem ok. When I start the car from cold ther pumps works, and until the fan enters the equation it works fine. Also, when the fan and pump are both on my wipers work very slowly.

I was wondering if this would be due to my alternator. This would make sense with the wipers slowing when the fan is on as the alternator may not be able to produce adequate power, but what about the pump cutting out when the fan cuts in? Could the voltage drop of the fan cutting in cause a lack of power to the pump?

This one's got me a bit puzzled!
Paul Grundy

Get out your schematic and trace the system wires until you find a common juncture...You'll most likely find a corroded terminal that's causing high resistance.
R. L Carleen

Check the voltage at various points in the circuit, particularly at the pump, fan, white and green sides of the fusebox and alternator with the engine running at a fast idle and the fan both off and on. It could be a bad connection just in the pump feed, and the normal voltage drop when the fans come in is causing the voltage at the pump to drop below its operating value. The pump is not fused, coming straight off the ignition switch. The wipers are fused, again off the ignition switch. The fan *should* be coming off a thick brown via its own in-line fuse, via a relay if you don't want it running when the ignition is off. Did you uprate the wiring from the alternator when you did the conversion? If not you are probably losing some voltage in that and the whole system voltage is dropping when the fan is on. Nevertheless I still wouldn't expect that to be enough to stop the pump, but I have no experience of that type.
Paul Hunt

Might want to check the ground on the fuel pump also!
jtm maguire

This thread was discussed between 15/07/2003 and 17/07/2003

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