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MG MGB Technical - Car Stalling - Mostly when hot

fuel pumpbr>Is there any obvious reason why when my mgb gt gets hot the car cuts out and will not start again. Here is the sequence of events

1. Car starts fine
2. Car runs okay
3. Car gets hot
4. Kenlowe fan kicks in
5. Between 30 seconds and 4 minutes later the car splutters and dies
6. If the fan kicks in immediately as the ignition is turned the car will not start. Otherwise the car will start fine.

Since this has happened I have started the car and let it get hot (just on drive way). The fan has kicked in and it
A Watts

The first thing when an engine cuts out suddenly is *always* to immediately look at the tach (electronic tach i.e. 64 or later (*always* give the year of your car, it saves a lot of questions and eliminates a lot of possibilities)) before doing anything else.

If the engine is still being spun by the momentum of the car, but the tach has dropped to zero, then there is a break in the ignition circuit through the switch, coil, points and distributor earth wire. If additionally the ignition warning light has come on, then you have lost the 12v ignition supply through the ignition switch.

If the tach is still registering, then the problem is HT or fuel. If, when the car eventually restarts, you notice that the fuel pump (assuming an original SU type) chattering away for a couple of seconds then the problem was fuel, and probably the fuel pump or its connections.

If it doesn't restart immediately afterwards, and you have a timing light to hand, then clipping it onto the coil lead and each plug lead in turn will tell you if it is coil (no flashes on any lead), rotor (flashes on coil lead but no plug leads), or distributor cap (flashes on some plug leads but not all but this usually gives very rough running and not total failure). The other cause of no flashing on the coil lead can be a faulty condenser, there are defective ones around these days (and rotors) and they can fail when hot but 'repair' when cooled down.

Much better to do a proper diagnosis than replace parts willy-nilly.

Paul Hunt 2010

This thread was discussed on 04/06/2010

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