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MG MGB Technical - Fuel Pump (SU) points

Greetings,

I have a 79 B, it's been running great, except lately no fuel is getting to the fuel filter at all. dry. The car has been parked for 2 months.
Also, the FUEL GAUGE does not register despite having 4 gallons of gas. Battery is now fully charged, and still no gas...ZS carb has been working fine.
Help! I hear these pumps usually do not need to be replaced, so any help is appreciated, so I could relay to mechanic.
Diana Ruth

Hi Diana,

I had a similar problem on my 1970 BGT, on closer inspection there was a kink at the end of the plastic fuel filter which was probably stopping fuel getting through. I guess your mechanic will have noticed something like that though!!

You should be able to hear the fuel pump ticking if its working, just before you turn the engine over at ignition. I'm pretty new to these cars but apparently the fuel pump is particularly temperamental, although I had heard that the one fitted to the american models is a little sturdier,

Good luck!

Tim
Tim J

What explains the Fuel Gauge not registering? I DID notice when I was running around on the highway that the gauge was 'not registering' and was all the way on Empty-- I ran the car all afternoon, and even stopped to fill up gas-- but even after that the Gauge just didn't seem to 'register' upon inserting/ turning the key. After being parked for 2 months, the car now does not start, gauge still not registering. I had charged the battery since it was dead to begin with.
Any tips on cleaning the points of these pumps ?
Diana Ruth

Hi Diana.

The classic temporary cure for sticking fuel pump points is the application of a Newtonian Pulse.

This is not difficult, simply give the body of the pump a sharp blow with a big spanner (imperial size, of course).
This is often enough to get a pump with sticky points going again.

HTH... Don
Don

A "big (imperial size) hammer is not necessary to get the pump started if iti is the points sticking, a screwdriver handle will do the trick nicely. The idea is to jar the points loose, not to beat the pump into a bloody pulp (I received a pump where the latter was done - all to no avail because it was an all electronic pump with noo points. Diana, I have sent you a fuel delivery troubleshooting guide via e-mail that may be of some help in diagnosing your problem. Cheers - Dave
David DuBois

Hi David.

I agree that a big hammer would be inappropriate, which is why I suggested a spanner.
Something like a 3/4 in af is about right in my experience.

Don
Don

also have your mechanic check Paul Hunt's site for fuel gauge diagnostic path..

http://www.mgb-stuff.org.uk
-Spanners
-Gauges
J.T. Bamford

Don - Sorry, I misread spanner for hammer. The pump that I received had been a victim of the large hammer, I even took pictures of the alloy body with all the hammer marks on it. Cheers - Dave
David DuBois

Hi again.

No prob.

The 'approved' tool for use on Morris Minor SU pumps is the starting handle.....

Don
Don

Hello Diana,

When my fuel gauge didn't register it was due to the wire connected to the tank sender unit being broken (corroded). Easy to spot and fix with a new spade connector. Hope its this simple!
Bumpkin

MGB fuel senders use a plastic float which is prone to leaking. Once it starts to leak it no longer floats and therefore always registers empty.
Bill Boorse

No visible fuel in the filter is not neccesarily a problem if the engine runs. A non-functioning pump is almost certainly nothing to do with a non-registering fuel gauge and others have dealt with how to deal with the pump. A 'sunk' float should always cause the gauge to register a very small rise when the ignition is switched on. If the gauge doesn't register at all it is probably a break in the circuit. With the ignitoon on connect a known good ground to the green/black wire on the tank just long enough to see if the gauge starts to move. If it does so the problem lies with the sender or the tank ground, if not then further forward towards the gauge.

If it rises then touch the green/black connector to a clean bit of the sender body, if it rises then the sender is open-circuit and must be changed. If not touch it to a clean bit of tank, if it rises then there is corrosion between the sender and the tank body. If still no rise the ground path betwene the tank and the car body is broken, there was no ground wire on late cars.
Paul Hunt

This thread was discussed between 11/10/2004 and 15/10/2004

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