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MG MGB Technical - fuel pump will not pump fuel

I have a problem that I hope somebody has a simple answer too. I have changed my old su fuel pump to a new contact less electric pump. It clicks away lovely when the ignition is on but doesn't pump fuel. If I take the pipe off from the tank and dip it in a container it pulls the fuel through, but as soon as I connect it to the tank it still clicks away but does not pull fuel through. I have taken the pick up from the tank out an as long as it is not actually fitted inside the tank works really well. I have blown the lines through, changed all the pipes an this is really starting to get me down, so any help would be appreciated

Thank you Rich
RJ Neale

Hi Rich,

Two things come to mind, the first is obvious, like you do have fuel in the tank.
Second you may have an air leak on the suction side.

Herb
Herb Adler

Rich - Are you sure that connection to the tank is sound? A slight tilt of the fuel line is all it takes to produce an air leak. If you have a good connection to the tank, then the pickup tube in the tank is the culprit. Cheers - Dave
David DuBois

Rich you say that you have taken the pick up tube out of the tank. How did you do this, I thought it was welded/brazed to the side of the tank. This tube must be the problem but you say you have blown it through and it's clear. There must be some debris or rust in the tank that is blocking the bottom of the tube, or if you have been able to remove this pick up tube it may be pointed upwards and pulling air. You could drain the tank and remove the bottom plug and try and flush it out.

Andy
Andy Preston

Andy, the later cars had the pick up pipe running through the fuel gauge mounting - that's how he has managed to take it out the tank. Also later tanks, and all replacement tanks, do not have a drain plug.

Rich, you must have an air leak between pump and tank, OR the pump can't pull the fuel up against the slug of air in the pipe. Is your pump under the car or in the boot? These pumps are not good at pulling fuel uphill and need to be nearly level with the bottom of the tank.

When I first fitted a Moprod pump it wouldn't pull fuel out of the tank, but I found that once the pump had some fuel in it, it was OK. You have run fuel through the pump so I am puzzled as to why it won't work in situ.
Mike Howlett

Just to revive an old thread. One of our members, cannot remember who, wrote about two fuel pumps, that could be energised independantly from the dash, so that if one pump failed 'on route', the other could take over till you got home again. I think this an excellent idea. Course it does not help if the pump is not picking up fuel! And the system incorporated a fuel petcock or in line ball valve so that you could change pumps without draining the tank ( you are correct all later tanks do not have a drain plug!) Still once all sorted, and whilst you are about it might be good to install now? Mike
J.M. Doust

Andy

You are not the only one who is puzzled, I actually managed to get the pump to work for about 3 seconds before it stopped again, its a Hella pump made on Germany and fits in the boot floor exactly as the original SU did using the same brackets and grommet. It will suck fuel from a can and if I put the pipes the wrong way round it blows bubbles into the can just will not work under any kind of pressure. I have run the fuel pipe from the tank to the inlet side as straight as I can and primed the pump it just will not suck. I have tried putting my tongue ( disgusting I know ) over the inlet when its running and can only feel very slight suction I am wondering if its the pump. I have spent 3 days on this now and the house, garden and garage stink of petrol. I need to get this sorted before the wife kills me. Can you recommend a pump that will do the job or do you have any other suggestions about what's up with mine


Rich
RJ Neale

Here might be a test; set the pump up at its normal level but run a fuel tube straight into the tank from the filler spout, now try the pump. If it manages this test then, the problem has to be at the pick-up end in the tank. Mike
J.M. Doust

Mike's test can be done easier by just dropping a flexible line from the pump to a can of fuel close to the pump.

Mike, the article you saw regarding a permanently installed backup pump could well have been the one on my website at: http://homepages.donobi.net/sufuelpumps/ Regarding the ball valve to shut off flow from the tank, while that could serve as an anti theft device, an easier way to stop fuel loss while changing a pump is to loosen (or remove) the fuel line at the fitting on then end of the tank. This breaks the vacuum in the line and prevents fuel from being siphoned out of the tank. I put the ball valve in place before I realized that there was an easier way to prevent fuel loss while changing a pump. Cheers - Dave
David DuBois

David you've just destroyed my supply of ball valves business! You are quite right! But I still like the ball valve, it looks so professional, it like says, I know what I am doing!'. Cheers Mike
J.M. Doust

Mike - Start marketing them as an anti-theft device (you can probably even double the price on the vales if you do - except to people who read these postings). Cheers - Dave
David DuBois

Rich says he took the pipe off the tank, which isn't the same as taking the sender and pick-up pipe out of the tank. He needs to tell us exactly which he has, cars with the pump electrical end in the boot used both types according to year. If it is the former case, and air blows through the tank pipe (it *should* make bubbling noises if there is fuel in the tank and no hole in the pickup pipe), then I suspect the pickup pipe inside the tank is perforated above the current level of fuel. Game over (for the tank).
PaulH Solihull

Hi Paul I have a 1975 first of the rubber bumper model but unusual as most the parts are a mix of the 2 models interior dash board etc are chrome bumper as is all the brakes etc. I think they were just using up the old bits and the fuel pipe and sender are in one unit held in place with an o ring and rubber gasket ( both have been replaced ) There is no perforation in the pick up pipe in fact it looks brand new as does the tank itself it is almost as if the pump breaks down when under any pressure I think I am going to bin it and look at a straight electric pump it appears to be the flavour of the month on the net. Thank you all very much for your help and advice but I think I have met my match with this one. One final thing can anyone recommend an electric pump that they have used and actually works

Rich
RJ Neale

Rich you can't go wrong with the original type SU fuel pump. I have them on all my cas. They work forever and can easily be repaired with advice from Dave DuBois. BTW check out his website; there isn't anything he doesn't know about SU pumps.

Andy
60 A Coupe
67 B
74 GT
Andy Preston

The combined sender and pick-up pipe wasn't used until August 1976. An original SU is best, but the Hella looks to be a copy mechanically, although the electrics end is different. If the Hella sucks from an external container, but not from the tank connection, then it's difficult to escape the conclusion that it is the tank connection that is at fault, not the pump. Why did you replace the pump in the first place?
PaulH Solihull

Paul told you the thing was a mix and match, The tank etc was fitted when I brought the car around 18 months ago as a non runner project, the original SU was fitted to the car but was totally shot, the outside had corroded through but as this was the least of the problems I left it alone, I got the engine working by simple gravity feed directly into the filter and carbs and she ran perfectly to move her around the drive and garage. anyway I have now replaced sills, wings, brakes,suspension you name it its all new and I am waiting to get it painted, I thought it would be a nice idea to drive it to the paint shop or at least to the Mot station and my problems began, I thought that by buying the Hella pump I would get away from points failure but perhaps I will take Andy's advice and get a SU pump. Wouldn't trust this pump now even if it suddenly started working.

Rich
RJ Neale

This thread was discussed between 24/09/2011 and 28/09/2011

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