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
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