Intermittent power loss 1975 rb roadster

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Paul Scott
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Re: Intermittent power loss 1975 rb roadster

Post by Paul Scott » Tue Sep 11, 2018 8:33 am

I think its sorted now :-)

Done some fast runs this morning up & down a short piece of Dual carriageway. No cutting out!!

Thanks for your assistance.

I will get her out on a longer run after my holiday.

Paul
1975 MGB Roadster
Webguru for MGB Register

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Charles Farran
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Re: Intermittent power loss 1975 rb roadster

Post by Charles Farran » Tue Sep 11, 2018 12:38 pm

Hi Paul,
That's good news. Enjoy your holiday.
Cheers
Charles
1980 Roadster

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Paul Scott
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Re: Intermittent power loss 1975 rb roadster

Post by Paul Scott » Sat Sep 29, 2018 4:39 pm

Quick update....
Took her out for a 45 mile run today. No cutting out!!

So I think she's fixed :0)

Thanks again for your assistance !!

Regards
Paul
1975 MGB Roadster
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Paul Scott
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Re: Intermittent power loss 1975 rb roadster

Post by Paul Scott » Mon Apr 08, 2019 8:34 am

:0(
Hi,
It has come back.
So we did the MGB Register run yeseterday.
45 miles to starting point no issues. 40 miles into run stop for a lunch break. NO issues
Probably another 30 mins into run.
Tacho drops to zero & engine dies, ony for a few seconds.
This happened on a few occasions. Then it died for longer periods but came back to life. Moving cables under the dash made no difference.

Any Ideas?
Whilst the engine was dead I still had wipers & indicators. I tried the wipers and inicators action to see if they went dead too as they appear to have the same live feed as the ignition at the fuse box.

I guess if it died completley it would be relatively easy to fault find.

Regards
Paul
1975 MGB Roadster
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Vic Butler
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Re: Intermittent power loss 1975 rb roadster

Post by Vic Butler » Mon Apr 08, 2019 10:18 am

This is a "two pipe problem" to quote Sherlock Holmes.
As the tacho dies it's definitely on the LT side. Are any of the wires inside the distributor shorting out intermittently? You seem to have covered everything.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

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Paul Scott
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Re: Intermittent power loss 1975 rb roadster

Post by Paul Scott » Mon Apr 08, 2019 10:29 am

Good Question Vic !!

Could the condenser do this?

I need to pull the cap. But I have as you know already replaced the wire inside. It's so annoying, stopped would be an easier find & fix..

Looking at my previous notes , it does not look like I have changed the condenser since the issue started. I know I bought points - condenser - cap from dizzy DR. I have a green lead coming out of my dizzy which could be a lucas one I popped in early last year when.

Best get my large magnifier out!!

Regards
Paul
1975 MGB Roadster
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Paul Scott
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Re: Intermittent power loss 1975 rb roadster

Post by Paul Scott » Mon Apr 08, 2019 2:09 pm

Further to my issue..

No missfire.

Tacho dies - engine dies. No pop or bang and NO ignition light comes on. The overdrive stays locked in too..

Paul :0(
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Charles Farran
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Re: Intermittent power loss 1975 rb roadster

Post by Charles Farran » Mon Apr 08, 2019 3:09 pm

The Alternator light should come on if there is a difference of voltage between the two sides of the bulb which to work must mean there is a complete circuit made. You say that the light doesn't come on when the engine has died. I would check the YN connection on the "hot side" of the fuse box & also the YN connection from the same tab on the fuse box to the ignition relay. You might have a dodgy relay!
When the car is stationary / with the ignition off , try turning the key to the ignition on position before cranking. Can you hear the fuel pump ticking? The feed to the fuel pump shares the same double connector under the bonnet with the overdrive supply and the YN to the alternator light.
If you can't hear anything this may narrow down where the problem might be.
Cheers,Charles
1980 Roadster

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Re: Intermittent power loss 1975 rb roadster

Post by Charles Farran » Mon Apr 08, 2019 3:11 pm

Sorry, in my previous post all my references to YN should be WN !!!!!!!!!!!
Cheers,Charles
1980 Roadster

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Re: Intermittent power loss 1975 rb roadster

Post by Paul Scott » Mon Apr 08, 2019 4:11 pm

Hi Charles,
I might have added some confusion to my quest.

I have been advised it could be a fuel pump issue. So I am going to hopefully whip the cover off and take a look at the points. I cannot quite work out why no fuel would cut the tacho but I'm game & will have a look.

I have after some issues early last year replaced all of the connector blocks under the bonnet and in the boot due to tach & indicators cutting out. Cleaned and used dialectric grease when refitting.

Popped in a seperate ballast resistor, new fusebox and bypassed the loom ballast resistor. Thought I had fixed the original issue. But maybe not quite :-(

I only mentioned the ign light as an after thought. The light works as it should and guessing because the alternator is still being driven it stays off. Also because power is still being supplied the od stays locked in. I did turn the key off and the gearbox sound changed. Did not make sense at the time, but after thought was the od solenoid was being released as I turnned off he ignition

Regards
Paul
1975 MGB Roadster
Webguru for MGB Register

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