Hi All,

Please can anyone help with the following problem?

1988 2 Litre 740 Gl with Boch K Jetronic fuel system & B200E Engine

The problem is that the car is intermittently cutting out, there is no
particular time to it, i can be cruising or accelerating seems to make no
difference. I had to wait around 5 minuites, the car would start normally
and drive fine untill the next time it stopped.

We have got to the point now where the car will only run for 2 or three
minutes before the engine stops. It stops as though the ignition key has
been turned off, it does not cough and splutter it just stops dead.

When the car is in it's non running mode IE just after stopping in the
period that it wont start there is no spark to the plugs but at all times
there is a 12 volt feed to the coil. All the coil resistances are within
specification.

My thoughts are either, Faulty coil, Hall effect switch in the distributor
or the ignition control unit.

Can anyone help with a definitive test procedure to determine which is at
fault?

Many Thanks

Alan

Update 740 Intermittent cut out problem

thanks for the help everyone, problem turned out to be the ignition signal amplifier fitted to the NS inner wing. This was determined only after fitting a new hall effect switch. Such is life!

I had a similar problem. The car cut out after pulling a hill in warm weather, or would not restart after a brief interval of being parked after fully warming up. Tricky, because without the heatsoak the engine ran perfectly, and so the problem disappeared on all but the hottest days and if the car was parked for more than about 45 minutes. After going through all the FI relay jazz, etc. it turned out in the end to be the hall effect sensor on the distributor. In my case I put off accepting this until too late, when the car died once and for all in the blazing summer heat, 100 miles from home, with wife and 3 year old on board. Rental car, tow fees, repair at an unknown (but honest!) mechanic etc. proved that trying to save money by hoping for a cheap relay cleaning or replacement instead of a rebuilt distributor was ultimately counterproductive.

The fuel injection relay is a known source of this type of trouble. You need to remove it, inspect it, and re-solder the larger electrical connections on the printed circuit board. Remove the cover from the relay and use a hand lens to inspect the solder joints. I know that you will find cracked solder joints if the relay has not been re-soldered or recently replaced. Go to the 700/900 FAQ and look under Electrical and Relays.

Hi John,

Thank you very much for your reply.

After a long time testing the car, I know for certain when the car won't restart that their is no spark at the plugs.

Can you explain to me where the fuel injection relay would fit into this. Is it integrated into the ignition system in some way.

Thanks

Alan

Since there is no spark (watch the tach when you try and start it. does it move at all?) that points to either the hall effect sensor on the distributor or the power stage unit. I've got a 89 760 with the same problem, and narrowed it down to the power stage (thanks mcduck) by checking on pin 5 on the harness going to the power stage. Look for a pulsing 5 volts when the motor is turning over. Mine also shows a ground on pin 1, but i'm not sure if that's correct. I need to get a really good look @ the harness to see which wire goes where. Anyone have any good wiring diagrams for the ignition of these parts?

I HAVE THE SAME PROBLEM 2 YEARS AGO, IT MAINLY HAPPENS DURING HIGHWAY DRIVING AT SPEED 120KM, THE THE CAR WOULD SUDDENLY LOST POWER TOTALY AS IF SOMEONE JUST PULL THE KEY. THE SITUATION GRADUALY GOT MORE FREQUENT AND HAVE TO WAIT LONGER TO RESTART. THE PROBLEM IS THE HALL EFFECT SENSOR IN THE DISTRIBUTER .

GOOD LUCK....