MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Fuel or electric problem?

Would this be a fuel issue or an electric issue:

Started fine this morning. Engine ran perfectly for about half a minute, then died.
Tried to start - no way. Just cranked and cranked.

I disconnected a fuel line and turned on the ignition - fuel pumped like a firehose.

The fuel pump is ticking very fast - faster than usual.

Any ideas?

Bernie
Bernie Lowe

If the pump was running fast when you had the fuel line disconnected from the carburetors, that is normal. If it is running on when connected to the carburetors, then either you have a bad valve in the pump (unlikely as sit is pumping fuel when disconnected) or it is sucking air on the inlet side of the pump (a hole in the pickup tube in the tank, above the fuel level in the tank; a loose connection at the tank or the pump; a hole in the fuel line from the tank to the pump; or the gasket under the large domed cover on the right side of the pump that is held in place by a single 2BA hex head screw.

When you are cranking the engine, see if the tach is indicating any revs at all. If not, something on the primary side of the ignition is open. Cheers - Dave
David DuBois

Bernie

My rule of thumb is to quickly pull a plug and smell. If it's wet then probably not fuel. If the plug is dry then it is fuel.

Stick the plug in the lead and rest against the head and see if you get a spark when cranking.

Either way you will know in a minute system has failed.
A J Ogilvie

How did it die? Slowly and with increasing spluttering? Or suddenly like it was just switched off? The former is more likely to be fuel, the latter ignition. If you can always glance at the tach when the engine cuts out and see what it is doing while the engine is still spinning under its own momentum or the cars forward movement. If the tach has dropped to zero it's ignition supply (in which case the ignition warning light will be on as well) or LT circuit. If it's still registering then it is HT or fuel, or possibly an open-circuit condenser.

If the pump is pumping when when the pipe is disconnected from the carb then the pump is almost certainly OK, a carb or carbs with the float valves open is exactly the same.

Rapid clicking with the pipe connected in that case is more likely to be a float valve stuck open and overflowing, which if you have the charcoal canister takes some time before any appears on the ground. Could be flooding in that case. Also if the overflow/vent is blocked the floats won't be able to rise, nor will it overflow, the pump will pump straight into the cylinders.

I've never seen the tach registering when cranking, maybe the system voltage is too low for the electronics. The first test for a non-starter should be to clip on a timing light and watch for flashes while you crank, but again the car's own battery may not deliver enough voltage for the electronics (BT, DT), so you would have to use one of the older in-line neon lights, or power the timing light from another source. Flashes should be regular and consistent, four times faster on the coil lead than any one plug lead of course. Good flashes on the coil lead but not on the plug leads indicates bad rotor or cap. None on the coil lead is coil or ignition LT, and to diagnose that you need a voltmeter, but could also be condenser which is best checked by temporarily hooking another one up between the distributor wire and earth.
PaulH Solihull

This thread was discussed between 18/10/2010 and 19/10/2010

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.