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MG MGB Technical - Died in traffic

Today while driving my 1977 MGB it simply stopped. The motor died. So I pulled off the road and opened the bonnet, wiggled wires around on the coil, plugs, alternator, fuses, and anything else I could find. It started up and ran for another few miles before it died again. Same routine...wiggle wires, start up, drive a few miles, dies. This happened about six times as the sky was darkening (the Prince?) and a thunderstorm approached. After several wiggle sessions I think the culprit may be the cluster of wires connected to the alternator. I will check the connection soon, but wanted to get your collective opinion on other typical causes for this behavior.
I look forward to your thoughts.
Randy Olson
1977 MGB
1969 Jaguar E-Type
2000 Subaru Impreza (the least reliable)
randy olson

Randy, Overheating coil perhaps. While your wiggling the wires etc the coil cools down and then heats up again after a few miles. Hope you sort it. Chris.

Do you still have a points setup? If so try replacing the condensor, it's not uncommon for these to fail when warm, as they cool down the car will fire again. Only a few Pence (Cents) to replace so it's worth a try.

Mike BGT

Could also be the ignition relay.
rick ingram

Randy. Not the cluster of wires off the alternator in most cases. The battery is used to start the engine. This demonstrates, with a fully charged battery, between 12.0 and 12.5 volts in most cases. When the engine starts, the alternator takes over, running the various systems through that set of wires that you have been jiggling. If they were not connected properly, you would find that your battery was running the various systems.

When an engine is running on the battery, you will find some common symptoms. Exactly which you will see will depend on the length of the trip(s) and how fast the battery is being drained. One classic symptom is that the starter cranks slowly, sometimes not at all. (That is why the first step in dealing with a "starter" problem is to recharge the battery and test again.) On longer trips, the turn signals begin to not flash--not sufficient current available to trigger the flasher. Headlights become very dim, the windshield wipers are very slow, and the horn does not sound. Insecure wires (i.e. the plug in) to the alternator and a loose fan belt can cause these symptoms, as can a bad alternator.

Rick's comment about a bad ignition relay is something to look at. The ignition relay powers the "white wire" circuit, and its fused follow on, the green wire circuit. If the relay goes bad, it will cut power to the low tension ignition circuit and the engine will die.

Take the car out for a drive and see what happens. Do not take it anywhere where it would be dangerous to pull off the side of the road. Hope the engine dies. When it does, watch the tach, briefly. If the tach drops, immediately, to zero, you have a low tension ignition circuit fault. If the tach winds down with the engine, the ignition circuit is working and you have a fuel system related problem. Both can give the indications you describe.

Take a test drive and report your results. Also, let us know what distributor you are running and what is inside it. Letting us know what fuel pump you are running, what type of fuel filter you are running, and what carb is on the car would be of assistance in diagnosing the problem.

Les Bengtson

Did it stop dead, or splutter a bit.
I'm thinking fuel pump.

If you look at the rev counter, if it is still reading, whilst the engine is dieing, then it is not a fault with the wiring or points, but could be the coil, or HT components.

My favourite is an intermittent fuel pump.
Martin Layton

Have you tried wiggling the wires while it's running, to see if it stops?
Dave O'Neill 2

All good comments so far, and I have some things to check. However, I will have to do that a little later as I have 7 relatives here for my son's wedding using wedding cars sevenoaks tomorrow and things are a bit hectic.
Things I know: I added twin SU carbs and they run well, there is a Crane electronic ignition in place of the original dizzy, and the fuel pump is the electronic type. The ignition relay was replaced a few years back, and it should be OK.
I don't think it's a fuel problem. When the engine stops it does it sputtering.
Restarting, it seems like the battery is not really putting out a lot of power, but the car starts so easily that it wouldn't take much. The battery was new last year, so I can check the charge later today (maybe before the Rehearsal Dinner?).
Anyway, I'm impressed but not surprised at the responses so far. I'll check more later, but it's off to play a little tennis which was scheduled before the latest Dark Shadow passed over the B.
Cheers from sunny Ithaca,
randy olson

Could be all sorts of things. The first thing you need to do is what Martin said (and what I always say) and that is when the engine dies before you do *anything* i.e. while the forward momentum of the car is still spinning the engine, look at the tach and the fuel gauge.

If the tach is still registering you have ignition voltage, which makes the problem HT or fuel.

If the tach has suddenly dropped to zero and the ignition warning light is off, you have lost voltage from the ignition relay (77 on) or the path through the coil circuit is open-circuit.

If the warning light is on, on all models, the voltage from the ignition switch has failed.

HT is pretty easy to check - immediately it happens clip a timing light onto the coil lead and each plug lead and watch for regular and consistent flashes while cranking. If the coil lead is good but the plug leads aren't then the cap or rotor is probably breaking down. Check the heater valve, if this is leaking onto the cap it can cause it. If no flashing on either coil or plug leads it is either the coil, trigger e.g. points or electronic module, or connections. If the plug leads flash OK while on 1 and 4 just check the timing is about right.

Otherwise it is fuel. If it is the fuel pump when you turn on the ignition again, or when the pump suddenly starts working again, it will chatter much more than normal while it refills the float bowl(s).

Another fuel cause is the vent from the tank through the charcoal cannister blocked, if removing the fuel filler cap results in a rush of air into the tank that is it.

Other emissions paraphenalia problems can also cause it, by sucking the fuel out of the carb jet(s). You can eliminate that (if it still happens) by removing the hose from the float chamber vent pipe.

Paul Hunt 2

The test drive this morning was lucky...the car died! After driving about 6 miles I finally got it to stop. It caused the tach to stop immediately, I think. The first that I noticed the engine wasn't running was when I signaled to make a left turn and there was no indicator light flashing on the dash. i tried starting it a few times and it wanted to start but died immediately. Since I was on the road (no cars other than mine) I opened the bonnet and went straight for the ignition relay. I wiggled the wires around and the car started up. I drove home and sanded and lubed all the contacts on the relay. The car started right up again.
Now I'll do some more driving and see what happens. More reporting on the tests after the wedding in two hours.
randy olson

Actually, I drove the B about 15 miles just now and there wasn't a problem. It purred like normal. So hopefully the cloud has passed and it's back to the open road!
Thanks to all,
randy olson

check the points! I had the same problem on a rebuilt engine today , after much head scratching I found the wires that go on the 'floating spring' type points where earthing out, pulling the wire from the dizzy solved the problem for a short while, a bit of tape solved it permanently, I hope
S S Tew

If the tach dropped and you had no indicators either then it was definitely 12v from the ignition relay that was missing. You need to remove the relay and clean its spades, and make sure the spade connectors are a firmish fit onto the spades, pinching them slightly with a pair of pliers as required.

Whilst wiggling connectors may get you home, it certainly isn't a proper repair and will almost certainly occur again soon. From things like this Lucas gets it unwarranted bad reputation.
Paul Hunt 2

Check the connections on the starter where the battery cable attaches. The brown wires may still have slide-on connectors, and as the wires age and harden the connections may get loose and fall off occasionally. I have replaced them with eyelet connectors that fit to the post with the battery cable and bolted them all together. It may be one of the other suggestions, but I suggest checking this. Good luck! Matt
M. H. Dabney

This thread was discussed between 03/08/2007 and 09/08/2007

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