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Engine kept running with the key out ?

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RRman

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We just got a 1977 MUSRARD YELLOW MGB /bcforum/images/%%GRAEMLIN_URL%%/grin.gif !!! Stripped and ordered new interior(black). We finally got the engine running last night(electric ignition)!!! Something blew....but the engine kept running. Even with the key out!! We had to disconnect the battery before the whole thing blew. Ever had this happen??? Today my wife starts covering the seats.
RR Man
 
Pull the steering column cowl & check the ignition switch wiring.
 
I've seen something similar happen with a VW engine and a not-quite-right wiring job to the alternator.
 
Since it's a 77 I would guess the anti-run-on valve isn't working.
 
I ***think*** that there is a diode pack that may possibly be defective, allowing the flow of current to bypass the ignition switch. I seem to remember Twist talking about this phenomenon several years ago. Located on the passenger side of the firewall under the dash if memory serves correctly. And I saw Dennis Trowbridge make this repair to an MGB about 15 years ago....I wish I could remember exactly what was done.....

But then....I've been wrong before.

/bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
Rick, can you elaborate a bit on this? How is the current reaching the coil by bypassing the ignition switch if there's a problem with the alternator? Like Tony, I'd be inclined to look at the ignition switch itself.

RRman, when you say the engine kept running, was it running smoothly... or knocking and banging with the key turned off... filling your garage with the smell of half-burned fuel?
 
dklawson said:
Rick, can you elaborate a bit on this? How is the current reaching the coil by bypassing the ignition switch if there's a problem with the alternator? Like Tony, I'd be inclined to look at the ignition switch itself.
Click to expand...

As I said...I ***wish*** I could remember the specifics. I know that it was an easy fix....

I'm in Grand Rapids at the moment, and if I can corner Twist, I'll ask him exactly what the repair was on this incident.
 
Same problem with mine from time to time. Giggling the ignition switch with the key in it sometimes does the trick and the run-on valve has in the past been an issue to.

So do like Tony said & check the ignition switch and then go clean-up the contacts on the anti-run-on valve too.

Otherwose you'll just have to keep popping the clutch until you figure it out. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
Another question,
with the key off, if you connect the battery do all of the accessories come on (dash lights, radio, fuel pump, fan) or is it just the ignition?

I had a similar problem but it turned out the PO had swapped some wires after getting the car back from the paint shop. In short the headlight circuit was connected to the ignition circuit so when the lights were on so was the ignition(bypassing the key).

Rob
 
Thanks, Dave!

Take the "," out of the above link...

https://www.mgb-stuff.org.uk/

and you'll hit the site perfectly...

this is all ringing a bell....I know that there is something that was done beneath the dash to rectify (no pun intended) this problem... I WILL figure this one out!

/bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
rick_ingram said:
I ***think*** that there is a diode pack that may possibly be defective,
Click to expand...

That's the problem I had with the VW engine when I did an alternator conversion on it. There was no defect, things just weren't set up properly. As I recall I put a diode in series with the field pole and that solved the problem.
 
OK!!!!!!!!!!!!

Here's the skinny.....I was REALLY close, but do not win a ceegar!

RR Man...I'll bet the Zenith Stromburg carb is still on the car, right?

There are two diodes under the dash on the passenger side footwell. Dennis sacrificed one of these diodes and wired it into the yellow/brown wire of the alternator loom with the arrow of the alternator pointing towards the alternator.

This interrupts the flow of smoke from the alternator into the ignition circuit, thus eliminating the run-on.

Proper fix is a change of the anti run-on valve...as it works by pressurizing the ZS after the ignition switch is turned off, stopping the flow of gas into the combustion chamber.

There *may* be something lost in this translation....but is basically verbatum from Twist.

HTH.....
 
Thanks, Dave...see my disclaimer statement "There *may* be something lost..." ....

/bcforum/images/%%GRAEMLIN_URL%%/smile.gif

At least I now know that I didn't dream this fix!

/bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
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