Welcome to our resource for MG Car Information.



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 - Electonic Fuel Pump Woes

This is my first posting to the site, and hopefully someone out there can help me.

I have a 74 B with an electric fuel pump that began to cut out about a year back. When I turned the key in the ignition (engine hot or cold), the pump would sometimes not come on. If I turned the key to the off position and then back on, the pump would kick in and off we'd go. This got progressively worse, to the point where I would have to turn the key forward and back several times before the pump would kick in.

Towards the end of last year and into this season, the pump began cutting out while I was driving. I would pull over, turn the car off and back on several times until the pump kicked in, and then I'd be off again. The cutting out would happen at any time -idling at a stop light, cuising at 60 mph, or working my way through the gears.

Thinking it was the pump, I bought a new pump last Saturday. I hooked it up and low and behold it is doing the exact same thing as the old pump. I have since checked and rewired the ground (it was connected directly to the ground connection from the battery terminal to the car's frame, so I just put in a new wire), have tried setting the pump in different positions, and have even direct wired it to the battery in an attempt to determine if it was the positive lead that was giving me a problem. This seemed to work until I simulated turning the car off and on by attaching the lead, then un-attaching then re-attaching several times in a row. Once again, the pump would not kick in.

I have also noticed that if I give the pump a shake or a little whack when it quits, it starts up again.

Interestingly enough, my mechanic's B has started to have similar symptoms, and he is completely stumped on this one.

Can anyone tell me what might be happening?
G A Goldrich

Did you check the connections at the pump, in between the pump and the switch, and the ign. switch itself? After 29 yrs, the ign. switch could have grundgy contacts which could cause your problem. I just got through cleaning up such an ign. switch on a 73 MGB of mine and that resolved an intermittent wiper problem. Often, dirty, corroded, loose, broken, or threadbare wiring or connections/connectors are the real cause, rather than something these things supply.

If you can have this problem happen for you, and then crawl under the car and smack the pump with wrench or hammer handle and it springs back to life, it could be you need new contacts inside the fuel pump. If you replace the pump, you might seriously consider replacing it with one of the new ones with solid state switching. This seems to get rid of the dirty contact issue for most folks. Good luck!
Bob Muenchausen

G A,
Is it an electronic SU or a points type? The symptoms you describe are not unusual for an SU that is going bad, I've limped home on occasion with a rubber hammer next to me in the cockpit which I used to wack the pump every 25 miles or so! I am stumped by the new pump doing the same thing though...the only thing I could suggest is possibly the new pump is not up to would not be the first time a "new" item was defective, many rotors, caps & pumps suffer this malaise. Where did you get the pump? Might want to return it and try a new one??
Good Luck!
Robert Dougherty

Even new SU pumps come with a slip of paper saying don't return the pump as faulty before cleaning the contacts if it doesn't work. Monitor the voltage at the pump terminals (both) and if it shows 12v but still only starts with a whack or a shake then the problem is inside the pump, new or not. Hunt's Fifth Law: "Many break-downs occur soon after a car has been worked on; 'new' parts can be faulty when you receive them; 'new' parts will sometimes fail soon after fitting; 'new' parts almost certainly won't last as long as the originals."
Paul Hunt

You might try connecting a light to the wire that feeds the fuel pump (disconnect the fuel pump)
and see whether if it dims, winks, or reacts
intermittently with the key movement.

Check the voltage while you're there.
Daniel Wong

The title of the thread is "Electronic Fuel Pump Woes" -- is this an Su pump with solid state switching, an aftermarket Facet-style pump, or something else? And is the replacement the same time as the one it's replacing?
Rob Edwards


From your posting it seems that an external wiring fault has been ruled out. This leaves an internal fault, and as others have said it's unlikely on two pumps but always possible. Assuming the pump is the standard electric and not one of the solid state aftermarket ones that click constantly I can't help thinking that another explanation could be that the pump is stopping becuase the fuel line is getting blocked somewhere, just as it will normally stop pumping when the float chambers are full?
Steve Postins

A few years ago we had a customer with pum,p woes. Rec'ed it but he came back a week later with it playing up again. Checked everything out - pump worked fine every time. Went for a 1/4 hour drive and it played up again. When I went to undo the lines to remove it I heard a sucking noise - he had fitted a new locking petrol cap - it was un vented. No air in means no petrol out!!
Garth Bagnall

'Cept a 74 North American *should* have a non-vented cap as the tank vents through the charcoal canister.
Paul Hunt

This thread was discussed between 25/06/2003 and 01/07/2003

MG MGB Technical index

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