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MG MGA - COWS

In AA language (AAA for those of you in the US) that means Cut Out Won't Start!

This has happened to me on more than one occasion now, and I'm no nearer to figuring out what's causing it, other than knowing that it's electrical.

For the first 35 miles today, driving at 50-70 mph, everything was fine, with the engine running perfectly. Then, there was the slightest hesitation, which came and went. After another 5 miles, the engine was coughing and spluttering constantly and was struggling to rev, until it eventually cut out altogether and wouldn't restart. Having got it back home, some 3 hours later, it finally started again.

Any ideas what might be causing it? My 'shortlist' is faulty coil, condenser or rotor arm, but I'd appreciate any help in narrowing it down.

Many thanks
Robert Sinclair

How do you know its definitely electrical - fuel starvation, intermittent pump failure, carb floats not at proper level?
J H Cole

Coil overheating
Art Pearse

Coil or wires on the coil, capacitor, or maybe the little wire in the distributor? Have you checked the points gap recently?
Peter.
P. Tilbury

IMHO your problem has fuel starvation written all over it.
Probably a partially blocked fuel filter or something else restricting the fuel flow.
There is any easy way to check for this.
The next time you have this problem:-
1 switch off the ignition
2 remove the front float chamber lid to see if it is full of fuel.

If it isnt full then you have fuel supply problems, (the front float chamber runs out of fuel first as it is furthest from the pump). This causes the front two cylinders to begin to mis-fire first and if the fuel flow reduces further, the rear two cylinders then begin to misfire until the engine stops.

Let us know how you get on

Colyn
Colyn Firth

So what have you done to it since it has already broken down on you several times? I can tell you that Colyn's suggestion of looking at the bowls is good. I can also say that 80% of ALL SU problems (I'll include fuel system problems) are electrical. I've never heard of a fuel pump being ressurected after death. I have heard of coils and some other ignition components being temperature sensitive.

When was the last full tuneup and what did it include?
Chuck Schaefer

I have had a lot of trouble with SU fuel pumps on MGA's. They were a new type, intended to deliver more fuel, and from memory branded "HP". I doubt whether the makers thought we would be still using them all of these years later! I have been told that they are difficult or impossible to repair. I have fitted new electronic pumps to several of my cars (not just MGA's), much cheaper than getting SU's repaired (if poss) but they must be very low pressure. The pumps that I have used are called Fuelflo (made in NZ?) but may not be widely available.
Barry Bahnisch

fuelflo are excellent..and ca be bought on ebay at a discount.
Neil Ferguson

double check your point gap. They may be too close, causing shorting as they heat up. Also, check that your condenser hold down screw is tight.
Mike Parker

I am with Art on the coil particularly if it is a newer Lucas Sport Coil. I had two go bad in fairly short order. Very similar symptoms. If it appears to be the coil, consider replacing the high tension wires, especially the coil wire. I believe, but cannot be positive, that my very old wire set contributed to the problem.

Lots of good suggestions so only try one at a time. Too much tinkering in one session and you may not ever pin down the exact cause.


John
jbackman

As a rule of thumb I was always told ,and do subscribe to the view,if it's spluttering/hesitation /lumpiness it's fuel.If it cuts out instantly and with no sign of life trying to re-start it's electrical.

Very irritating,and can be dangerous on the road if it starts playing up whilst on the move.

Good luck.
M Blencowe

Thanks for all the advice.

I'm 99% certain it's not fuel, as the pump is working properly and there was definitely fuel in both float chambers when it last happened, so I can only assume it's one of the electrical components that's overheating - enough to stop it working, but not enough to make it fail altogether.

I've re-checked the points gap and tightened all connections, so now I'm going to replace the coil and HT leads before trying anything else.
Robert Sinclair

Inspect the distributor cap very carefully for any hair line cracking or signs of carbon tracking
J H Cole

Robert, I had very similar problems with my car and went down the same route of checking the ignition system over and over again.
I changed plugs, points, plug leads, condensers, distributor caps, rotor arms, coils ( notice the use of plurals here, I changed all these at least twice over) I even soldered up all the connections to the points to eliminate any bad connections.

All these seemed to fix the problem at first but it soon returned , it turned out to be an almost invisible piece of silicon in an fuel filter that would partially restrict the fuel flow. When the engine stopped, the pump would fill the float chambers fairly quickly and the car would then re start.

So it really is worth looking at the fuel flow, it may save you months of hassle. It took me 6 months of frustration before I found the problem.

Colyn

Colyn
Colyn Firth

I tried to edit the above post but I got distracted by the Olympic ceremony and left it too late to correct it.

To check this you need to switch off the engine immediately it cuts out. This is because when the engine stops, the pump then will fill the float chambers fairly quickly as the engine is not drawing any fuel.

Definitely worth checking

Colyn

Dont know why I signed my last post twice!
Colyn Firth

I had similar symptoms. It was the coil, which had slipped in its mounting strap on the generator, then worn through its casing due to vibration and in a spot where I couldn't easily see. The slow leak of oil caused it to malfunction when warm. Let us know when you solve this!
Tom Heath

I found in my late father-in-Law's garage bits an interesting ignition fault finding document, dating from 1956. Might be worth a read through: http://tinyurl.com/cd79x8w

Steve

(only signed once, but you are not alone Colyn. It sometimes happens to me when I edit my words before posting and the original signature slips out of view at the bottom of writing box)
Steve Gyles

I am really grateful for all the advice given (and for that 1956 fault finding article, Steve!)

I've replaced the coil and all HT leads and everything is now working normally. Admittedly, I haven't taken her for a long drive yet, because of the English summer weather we're having here, but all being well I'll be doing that later this week. Fingers crossed!

Robert
Robert Sinclair

Robert, if the fault comes back, change the rotor arm. Some of the modern black are absolute rubbish, fit a red one.
Lindsay Sampford

Fuel tank not venting?
Richard Atkinson

Robert

Following on from that fault finding article above, I made up a very simple wire continuity checker that I carry around in the car. See picture.

Steve

Steve Gyles

This thread was discussed between 26/07/2012 and 02/08/2012

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