On Wed, 11 Feb 1998 DANMAS@aol.com wrote:
> Bob Torrens wrote:
>
> "I have a '78 MGB that refuses to stop - sometimes! The ignition key is
> removed and one of two things happens. Either the car continues to run or
> within 30 seconds after removing the key, the ignition light and cooling fan
> come on."
>
> To which Bob Allen replied:
>
> "Have your alternator checked. Leaking diode."
>
> And Art Pfenninger replied:
>
> "Bob when you say continues to run, do you mean it runs as if the ignition
> is still on? If so you need a diode spliced into one of the alternator
> wires. What is happening is the alternator is sending power back into the
> run on valve and it continues to run."
>
> Bob and Art,
>
> I'm afraid you have me stumped on this one! For the life of me, I can't
> figure how either of these could be the problem. When you shut off the engine
> in any MGB, the alternator continues to produce 12 volts for as long as it
> takes for the engine to coast down. The only thing that keeps this 12 volts
> from being fed to the ignition system is the alternator warning light.
> Without the isolating function of the warning light, you would never be able
> to get the engine shut off. With the warning light, nothing else should be
> required.
>
> Since the alternator is producing 12 volts in the first instant after the key
> is turned off, it would not matter if the alternator diodes were leaking or
> not - 12 volts is 12 volts, regardless of how it came to be there.
>
> The anti-run on valve is on the opposite side of the warning lamp from the
> alternator, so it would not receive voltage from the alternator anyway.
> Besides, the anti-run on valve only shuts off the fuel, not the ignition.
> Even if it were to stay open, the engine would only *diesel* at worse, and
> would not run smoothly, nor run very long. If it were the anti-run on valve,
> the problem would exist in all of the later MGBs, and would have been there
> from the beginning.
>
> What am I missing? Is there some tricky circuitry on the later MGBs that I am
> overlooking?
>
> Dan Masters,
> Alcoa, TN
>
> '71 TR6---------3000mile/year driver, fully restored
> '71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
> http://www.sky.net/~boballen/mg/Masters/
> '74 MGBGT---3000mile/year driver, original condition, slated for a V8 soon!
> '68 MGBGT---organ donor for the '74
>
I had the problem of my 77 not shutting off when the key was turned.I
asked John Twist what the problem was when he was in Buffalo last summer
and thats the explaination he gave me. I followed his advice and the
problem was fixed. With the help of a list member that supplied the needed
diode I cut the wire and spliced it in and ended my problem for good.Who
knows...
...Art
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