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MG MGB Technical - ALTERNATOR WOES

ALTERNATER WOES – HELP
I have a problem with my MGB GT V8 conversion, .which results in the car misfiring at acceleration speeds, with the fuse in the alternator circuit eventually blowing on a regular basis, like every 20 minutes, but works OK at night with the lights on. The original alternator caused the ignition light to flicker on start up and on tick-over speeds, so I changed the alternator and bought a new 55 amp model. Everything worked OK for a couple of miles, the ignition light did not flicker at all, and there were no miss fires during hard acceleration. Then it all went wrong again the ignition light came on, and on inspection the in line fuse had blown again. Now all my old symptoms have returned again with the new alternator, the ignition light permanently flickers on start up and tick-over, and the car misfires badly on acceleration, with, the fuse blowing on a regular basis.
Can anybody offer an explanation, or a solution to my woes please. Jack
J N Martin

Is the engine grounding strap installed properly?
Curtis Walker

Jack - which model was your car before the conversion.
Which timing cover are you using and what size pulley on the alternator ? Is their an internal or external voltage regulator ?
Roger
RMW

What line is the fuse on? There shouldn't be a fuse between the battery and alternator or alternator and starter. There should be multiple lines off the alternator supplying power to various locations. We could better help you with more details.
Jeff Schlemmer

As Jeff says, where exactly is this (non-standard) fuse and what rating it it? Blowing implies excess current, and if its rating is 40 or 50 amps or more then that implies a significant short. Such a short could also explain the misfire and the ignition light flickering. Excess *voltage* from the alternator can also cause excess current, and that would tend to be reduced by running with more load i.e. headlights on.

If the flickering and misfire still occurs after the alternator fuse has blown (if indeed it is in the alternator output wire) then that implies a short is the problem (out of the two scenarios above, there could be others) and it is on the battery/solenoid/load side of the fuse.
Paul Hunt 2

Before you condemn the alt make sure your battery is taking a charge. I had the same problem w/my Datsun Roadster and it was caused by a defective battery and my alt was trying to charge it and repeatedly blew the 40 amp inline fuse I installed. New battery solved the problem.

Also check for voltage output of the alt as that can cause similar problems like blowing fuses and relays as well as everything else.

I also like to run a 10 gauge ground wire from the alt body to the car body - never can have enough grounds IMO.
Mike MaGee

This thread was discussed between 14/09/2005 and 16/09/2005

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