1978 MGB Motor won't stop with key removed

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1978 MGB Motor won't stop with key removed

Postby gfleblanc » Wed Mar 29, 2006 4:21 pm

I just replaced my fuel pump with an inexpensive electronic pump. I've been told about a wierd electrical design problem with 1978 thru 1980 MGBs which allow this under the right circumstances. I can actually remove the ignition key and the car runs until it burns the fuel in the lines since the fuel pump does stop). It'll go 20 to 30 seconds!! I believe it has to do with the grounding of the pump and a path whereby the current gets back to the ignition system.

Please, if you are aware of a fix to this let me know.

Thanks.

George
gfleblanc
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Problem Solved

Postby gfleblanc » Thu Mar 30, 2006 11:12 am

I found the solution on one of the MG tech topics sites. I had installed a new alternator and the output was increased over the original. This coupled with the installation of the new fuel pump allowed stray current to find a path back to the ignition system after I removed the key. The solution was to add a 3 amp diode to the brown/yellow wire to prevent this from happening. I didn't realize how common this was in the later model MGBs.

Cost was $1.59 from RadioShack (took 5 minutes to install)!! Diode P/N IN5404.
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