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MG MGB Technical - engine dies

Dear all
I'd welcome any ideas as to the cause of this problem.

A couple of days ago I had travelled about ten miles, car had been fine and out of the blue the engine faltered briefly and then died. The car restared on the choke but wouldn't run - it seemed to die when I pressed the throttle.

The car had not long been back from the garage having repairs to the rear end - I had had a shunt (waiting at a pedestrian crossing a guy ran into the back of me). These repairs involved removing the petrol tank. I had used the car a few times since getting it back but I suspected dirty fuel. There was a lot of rust sediment in the fuel bowls and bits could be seen in the fuel filter. The next day I cleaned it up and the car restarted and seemed to idle ok. 100 yards down the road it died again. Same symptoms. Got it back to my garage. Left it a couple of hours. Switched ignition on - fuel pump ticked for 30 seconds or so. Engine started and idled ok for 10 minutes. Reversed up and down drive and seemed ok. Did however notice that the vacuum pipe at the distributor was disconnected. Could this be the cause of is it more likely contaminated fuel?

Have not dared venture out yet until I feel I have got to the bottom of the problem. Had enough getting stuck at the side of the road.

The car is a standard 66 BGT, positive earth, points etc

Thanks for any ideas
Richard Atkinson

Has the filler cap been replaced? MGB"s need a vented cap . Does the pump tick when engine is stalled? If it runs all the time it could be that the pipe between tank and pump has cracked. If it does not tick, disconnect pipe from carbs and check for fuel flow, if still no ticks try removing inlet pipe at pump and check for fuel, (pipe may be blocked possibly in the tank). If all checks out O.K. try cleaning thepump points. It definately is not the vacuum pipe on the distributor. Jim
jim soutar

Richard - See the article, Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my web site at: for tips on troubleshooting the fuel system. Jim's suggestion of the filler cap and/or cracks in the inlet line from the tank to the pump are good places to start. Cheers - Dave
David DuBois

Jim, David - thanks for the suggestions. The first time it happened I checked the filler cap and no inrush of air. I'll run through the checks in your article David and check for splits as you suggest. What puzzles me is why it ran fine in the garage and when I got out onto the road last night it died on me? Is there anyway is which it could be load related? Having said that it wouldn't idle once the problem had occurred.

Thanks again
Richard Atkinson

Could be that the rear end collision disturbed a lot of muck in the tank and this is causing a blockage which is bourne out by the rust and sediment in the float chambers.

Could be time for a new tank, which would be probably no dearer then removing and cleaning the old one which may be well passed it's sell by date, also good time to replace fuel lines and filters if not done recently.

Kevin Jackson

Just in case it is something totally unrelated to the crash / fuel; replace the rotor arm as a precaution. they have a habit of developing hair line cracks which open up as the engine gets to temp - assuming you have a rotor arm of course!

Better still, get a luminition.
N Poulton

How about trying a cheap plastic fuel filter - that'll rule out dirt in the fuel as a problem. If you've dirt in the bowls then the current filter is not working.

I started the car this morning and and it idled in the garage for a few minutes before the fault then occurred. The engine stuttered and then stalled. I re-started it once or twice and it stalled. I switched the ignition off for a few minutes and then back on - no clicking from the pump. I removed the fuel line at the rear carb and no fuel coming out. The pump body was warm. It didn't respond to a tap or two. I checked I had a power supply to the pump before disconnecting the in and out fuel lines to the pump. Switching on the ignition - the pump did not click so I suspect a faulty pump. Having said that just tried switching on the ignition after a few hours and the pump clicked. So it seems it is failing once the pump warms up. I'll remove it from the car and see if there is anything obvious before replacing it.

Great advice guys - many thanks. Richard
Richard Atkinson

Check the valves in the pump. They most likly are full of crud from your tank. You may have to remove and clean and possibly seal the tank itself.
conrad sanders

I partially stripped the pump last night. Very little crud in the inlet chamber or in the metal filter on the inlet side. The points looked worn but not too bad. I have ordered a replacement set from Burlen and I'll see what difference they make.
Richard Atkinson

Richard - "The pump body was warm." That says you have a clog on the inlet side of the pump, probably in the line from the tank to the pump or in the pickup tube in the tank. Another indication of a clog in the line from the tank, is if you didn't have fuel running off your elbow as you disconnected the line from the tank from the pump. (While you are troubleshooting the problem, don't leave power on to the pump for more than 2 minutes at a time unless the pump is running. If the power is left on for longer than that while the pump is stalled it can damage the pump). As someone suggested earlier, the rear end hit probably stirred up some crud in the tank that is causing the clog. You may want to remove the fuel gage sending unit and look in the tank to see if the filter screen at the end of the pickup tube is covered with something. Next, remove the fuel line connection at the tank and see if you can blow through the line and back into the tank - this will tell you where the clog is (or possibly clear it). Cheers - Dave
David DuBois

Thanks Dave. I did get fuel running down my arm and quickly rushed to cover the fuel filler to stop air getting in. My guess is the pump was warm because it was working before it stopped. Having said that I agree that the possibility of crude being stirred up in the tank is one that has to be ruled out so I welcome your suggestions about checking the filter for the sender and blowing through the fuel line.
Richard Atkinson


Had a rear fender bender, if I read correctly, and now appears to starve for fuel after getting out of the body shop. Suggest you check the black ground wire in the trunk usually found under the lience plate screw or boot latch hook. May not have been reinstalled, wire broke or not a good ground path. May have been mentioned above and I overlooked. I added a seperate ground wire right from my fuel pump body to mount to body bolt as added ground path. Not crazy about original set up and has got me a couple times while getting car ready for body shop and stripping car of lights and such.


Fred Wright

"I did get fuel running down my arm and quickly rushed to cover the fuel filler to stop air getting in"

An easy way to avoid the bathe in fuel is to remove (or just loosen) the fuel line fitting at the tank. the only fuel that will run out then is what is in the line.

The fact that you got fuel running out of the line indicates that there is no clog in that particular line. The fuel pump (if it is a SU) should not run warm from normal running. It will heat up if it is stalled in a current on condition (points stuck closed or a clog on the inlet side of the pump. In this condition, the pump will get very hot in a relatively short period of time (I have a temperature monitor that I put on the pumps that are running on my test stand. I have it set to shut the power off if the coil housing gets above about 140F). The only other time that the pump heats up is if it is running wide open (no fuel being pumped or fuel pumping out of the end of the line on the outlet side with no float bowl to shut it off). This will result in a pump that gets warm to the touch, but not hot. If that is the condition that you have (pump running constantly), look for an air leak on the inlet side of the pump - like perhaps, a crack in the weld holding the fitting on the side of the tank. Cheers - Dave
David DuBois

Update and further problems

Replaced the points in the pump (with new from Burlen). Refitted pump to car. With ignition on the pump ticked merrily away (no fuel lines connected). I then connected the fuel lines. Turned ignition on, red charge light on dash on, fuel pump ticked quickly before slowing and finally stopping. I could see fuel enter the clear filter just before carbs.

Then I went to start the car, turning the ignition key and nothing at all happened. No turn of the starter motor, nothing. I switched off, siwtched back on - charge warning light on, went to start, nothing again. Now the charge warning light will not illuminate. I have no lights, side or dipped. I have 12V at the solenoid and at the three brown wires at the top fuse(of two).

Two additional things to mention. I had a headlamp blow the day I tested the car (the day it broke down - but I did have sidelights and the other headlamp was working). Also, as I was disconnecting the battery at the earth (car is + earth) - before disconnecting the fuel lines to test the fuel pump - my spanner caught the terminal of the next cell momentarily and I had a couple of sparks.

Any advice very welcome.

I cannot understand why I have no lights if I have live brown at the fuse (unless my light switch has failed) and why I no longer have a charge warning light. Unless both switches (light and ignition) are now stuffed?

Richard Atkinson

Solved the (electrical or perhaps dim owner) problem. The earth connection to the battery post was not a good one - good enough to give me 12V but not enough to start the car. Cleaned the post and clamp and made a good tight connection and the engine started and runs, all lights working. I'll leave it until tomorrow to test drive the car - just in case the pump packs in or something else breaks... It is very cold in London this evening!

Richard Atkinson

I found out that if a poor connection is supected on the battery just feel the terminal. If either is warm or hot then there is a bad connection.

When I was a student I once waited 5 hours for the AA to arrive as my B had died and ten seconds later after he had found a hot terminal I was back on the road!!

D M Tetlow

FWIW1: Symptom of a bad battery connection, or at the solenoid, is that the ignition light glows but goes out when you turn the key to crank. Similar to a flat battery expect that with a bad connection it may not immediately come back on again when you release the key from the crank position.

FWIW2: In your 31st Jan post if the engine has just been running the pump is unlikely to click when turning the ignition back on, even if the pump is working as it should. Several minutes later, or hours if the engine was still cold when tuened off, it may only click once or twice. However if it chatters away like mad when turning the ignition on after some time then that does indicate the pump had failed and the carbs had emptied so stopping the engine.

FWIW3: If the engine dies when you are driving along immediately look at the rev counter before doing anything else. If the tach has dropped to zero while the momentum of the car is still spinning the engine then it is an ignition LT problem. If the ignition warning light is glowing as well it is the supply from the ignition switch or relay that has failed. If the tach is still registering then the LT is OK, so could be HT or fuel. If you carry a timing light you can check the HT by clipping the light to the coil lead and each plug lead in turn, and watching the flashes as you crank. If you get them regularly and consistently, it is probably fuel.
Paul Hunt

For the archives - replaced points and the pump seems to be working ok - seems to tick much faster when the ignition is switched on in the morning now!
Richard Atkinson

This thread was discussed between 30/01/2009 and 16/02/2009

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