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MG MGB Technical - 79 B/not starting with assorted other ills

I have a '79 B. I drove the car on Thursday evening and parked it because the ignition light glowed throughout my half hour drive. I checked the alternator belt and found it somewhat loose and adjusted it.

When I attempted to start the car to see if the problem was solved, it would not start. The new (less than 2 month's old)electronic SU fuel pump does not click. I checked that there is power at the White lead to the fuel pump and my tester glows very brightly. The battery cranks the engine and seems to have a full charge.

On my last long trip in September, the fuel gauge did not function properly. Upon first starting the car, the fuel gauge did not show any fuel reading. After a short time, the gauge showed a half tank of gas or less, even immediately after a fill up. The gauge showed no reading during my Thursday night drive.

I'm stumped. Is it possible that all of these problems are related? If not, is it possible that my electronic fuel pump is defective? All of my dash lights function, as does the tach. The only electrical line touched during the process of adjusting the alternator belt was the water temperature gauge connection on the block.

Any help in diagnosing these problems would be greatly appreciated.

Charles Tregidgo

I forgot to mention that I also checked the inertia switch under the dash. It is fully depressed from what I can tell.

Charles Tregidgo

Hi Charlie.

Is the temp gauge reading normally ?, if not you may have a problem with the instrument voltage regulator or related wiring.

If the temp gauge is OK :

I believe the fuel level sender and the fuel pump share the part of the loom that goes to the rear of the car, check for damage or corrosion OR there may be a bad earth in this area. Do all of the rear lights work correctly ?.

The fact that the engine cranks normally suggests that the engine earth strap, battery earth strap and +12V cable are ok, but take a look anyway.

HTH.. Don

If you checked for power at the terminal on the fuel pump try checking the fuel pump ground circuit. You could have two problems or as Don said it may be in the loom that feeds the rear of the car.

Clifton Gordon

Check underneath the car to make sure the
separate ground wire is attached to the SU
pump. The electronic pump can certainly go bad.
Not sure if anything can be done with the
electronic version other than replace the

The fuel gauge sounds like a separate problem.
Usually the float has a leak causing the
empty or near-empty readings.

"usually the floak leaks..." Sorry, I'm
referring to the fuel gauge sender unit, not the
gauge itself. To check, ground temporarily
the connector to the sender unit at the
gas tank, and see if the gauge needle starts
rising fowards full. If so, problem is clearly
with the sender.

Charles - try the pump with the ignition on by disconnecting the fuel line by the carb(s) - you should get a reasonable flow.

The guage can often be the fuze (second up from bottom) - clean the connectors with emery cloth or the connector on the side of the tank - more elbow grease - or as Ronald suggests - the unit itself - unlikely


Thanks to all for your comments. I'll work on the car later in the week and let you know the results.


Charles Tregidgo

A faulty ignition relay will cause the fuel gauge not register when turning on the ignition, and failure to start, although it will crank just fine. If the wipers, heater fan, stop lights, reversing lights also don't work then it is almost certainly the relay or associated wiring. The fuel pump should deliver at least 1 pt per minute at the carbs with minimal bubbles. Once it has pressurised the system it will not click again until some fuel has ben used, unless the ignition is left off for some minutes. Even then it may only click once and cn easily be missed.
Paul Hunt 2

This thread was discussed between 30/10/2005 and 03/11/2005

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