Fuel pump problems

[IanW]

What a frustrating evening. SWMBO took the Stag to work today. Early evening, I get the plaintive phone call - thinks she's run out of fuel. I set off on a gallant mission with fuel can in hand, but to no avail.

SU fuel pump is ticking away merrily and isn't stopping. I disconnect the pipe by the fuel filter in the engine compartment and find only little splashes of fuel coming out. These stop eventually and the pump is just pumping little gouts of air. If I obstruct this pipe the [pump pressurises and cuts out (as it should) so presumably no leaks present between pump and engine compartment. Disconnect the banjos. Tank side is wet with fuel, but delivery side has very little in it. No obvious leaks in the plastic pipe from the tank to the pump. No blockages. Take out and check the metal pipe in the tank itself - all appears OK. And yes, there is fuel in the tank.

Call for recovery and two hours later we're home. Fit spare (old) fuel pump, but that's expired during storage and doesn't respond to "subtle" prodding with a small hammer.

So.......anybody any ideas? Do I need a new pump? Is it feasible that the diaphragm has failed in the pump (if there is one)? Is it worthwhile taking the thing apart?

I'm stumped. Ian

[martin]

Hi Ian, you say it's an SU pump, then it does have a diaphragm, they can fail over quite a long period till suddenly they can't put out the needed volume. From this distance, that would be my best guess, I've come across it on other folks cars a few times. LD do a well priced replacement. Martin.

[redstag]

Mine failed in France last year. It just kept ticking and no fuel.
When I stripped it recently one of the little one way valves had split. I replaced it and it seems ok now so it's gone into the boot as a spare for this years trip to France.

Pete

[IanW]

Thanks Martin. I've found a parts diagram for the pump (AUF300) and will have a delve in the morning. Do you think it's worthwhile trying to fix it or am I better off getting new?

Ian

[IanW]

Pete,

Just found reference to the valve question on the MG website - these pumps were fitted to later MG models as well - which appears to give the same symptoms as the diaphragm failure. I'll see what I find when I take it apart tomorrow.

[V Mad]

Dont try to fix it, bin it!

[GDPR]

I had a lump of debris from the tank stick in the pump inlet valve and give exactly these symptoms...... worth unscrewing the valves and checking.....

[martin]

I kinda go along with Russ, just to add, when/if you re-assemble, do so using PTFE tape, they can be a bugger to seal again. If you find a failed valve or diaphragm, bin it, you've still got the old points and other bits that can go. Good luck, Martin.

[IanW]

Thanks for the ideas everyone. The plot thickens (...and that's got nothing to do with someone surreptitiously dumping topsoil on my allotment).

Everything inside the pump looked OK (Should do - it's only four years old) so I pulled the fuel line off the tank and put it into a can of petrol. Lo and behold, fuel pumps fine.

I wonder if it's a break in the metal pipe that dips into the tank - perhaps concealed behind the nut that attaches it, so I've removed that and try to pressure test it (OK, I block one end and blow down it!). No leaks apparent.

The fuel gauge is showing a quarter full and the fuel light isn't on. The fuel light is working - I had to take the tank out to remove the metal dip pipe and tried it out by tipping the fuel to one end of the tank.

Any ideas where to go from here? I might put more fuel into the tank and see if there is some issue with the reach of the dip tube, but don't understand why that should happen suddenly.

[martin]

Don't forget that in service, the pump has to lift the petrol and move it the length of the car, it may still have enough grunt to work as you describe, but not under operating conditions. Martin.

[jakesmig]

Did you try blowing back down the feed pipe to the tank?
John.

[martin]

Did you try blowing back down the feed pipe to the tank?
John.

OOOOOH - - - - - don't like blow back !

[IanW]

Yes I did. I could become my own best friend at this rate - just need a more flexible back.

[stag157.7]

Thanks for the ideas everyone. The plot thickens (...and that's got nothing to do with someone surreptitiously dumping topsoil on my allotment).

Everything inside the pump looked OK (Should do - it's only four years old) so I pulled the fuel line off the tank and put it into a can of petrol. Lo and behold, fuel pumps fine.

I wonder if it's a break in the metal pipe that dips into the tank - perhaps concealed behind the nut that attaches it, so I've removed that and try to pressure test it (OK, I block one end and blow down it!). No leaks apparent.

The fuel gauge is showing a quarter full and the fuel light isn't on. The fuel light is working - I had to take the tank out to remove the metal dip pipe and tried it out by tipping the fuel to one end of the tank.

Any ideas where to go from here? I might put more fuel into the tank and see if there is some issue with the reach of the dip tube, but don't understand why that should happen suddenly.

there have been problems where the fuel pick up pipe is not long eneough to reach the bottom of the tank
i know two members that cant let thier car get below 1/4 tank
might be something to do with the aftermarket fuel tanks

you can tell these because they have no fuel return pipe blanked offf at the top of the tank

stick some more petrol in


alan

[flying farmer]

I once had a similar problem on my V8 engined Toledo with a Facet pump. Somehow the arse end of a wasp had got into the fuel tank and occaisionally blocked the pipe. Pretty unlikey to happen to anyone else though!
I have heard of the pipe going into the tank being too short and needing three or four gallons to reach it, the guy rebuilding the 4X4 stag engined estate had this problem recently, but the only way this would happen on a regularly used car would be if the fuel gauge started over reading due to voltage regulator problems, but I think the low fuel light would come on regardless
Neil