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MG TD TF 1500 - Fuel pump problems

The car has been hard starting for a while now, but always ended up running fine after a few attempts. But this morning the fuel pump just clicked away insanely for several minutes till I shut it off with nothing started. So I took off the fuel line on the carb and presto, the pump is not pumping fuel.
So electrics fine, pump is working, no fuel coming through. I checked the filter in the pump, it looked nice and clean.
I believe there is a small filter where the gas tank connects to the fuel line? I can check this, but if we assume it is the pump, what has happened? Has it lost its prime or burned through a diaphragm?
This pump was optoelectronically converted, so it's not a points issue.
Geoffrey M Baker

Torn diaphragm?
Jim Merz

Geoffrey - You can pretty well rule out a clogged filter in the tank by the fact that the pump is running. If the filter in the tank were clogged, the pump would stall in a current on condition and get quite hot. Possible causes for the symptom you are experiencing would be an air leak on the inlet side of the pump - check all of the fittings on the fuel line from the tank forward, especially the inlet line to the inlet fitting in the pump and the filter plug in the pump (you might want to check the amount of fuel is in the tank). The other possibility is some debris in one of the valves inside the pump, holding it open so that the pump can't develop a vacuum to draw fuel into it. A split diaphragm is highly unlikely in a pump that has only gone four years after being restored. While it is always possible for that to happen, if it did, you would see fuel leaking from the vent hole at the bottom of the coil housing.

I would suggest that you remove the fuel line from the outlet side of the pump to the rear carb (remove it from the carb) and direct it into a container, then turn the ignition on and see if the pump starts sending fuel through. This is a bit of a long shot, but if the needle valves in the carburetors are stuck closed and the fuel in the lines to the carbs evaporated, it is possible that the pump will keep running the way you describe.

I all else fails, send the pump back to me and I'll check it out for you under warranty. Cheers - Dave
D W DuBois

Well, it is not the diaphragm. That looks brand new. As does most of the interior of the pump! I'm leaning towards an air leak.
There are 7 gallons of fuel in the tank.
There is certainly always the possibility of debris, but like I said, it looks very clean! Dave, the pump sends fuel through, it just takes a long time to do that. What's the best way to check for an air leak on the inlet side?
Geoffrey M Baker

Well, I checked all the fittings between the pump and the tank and used ptfe tape to seal them and that made no difference. Pump is just not pumping, but is trying!
Arggg... tomorrow is another day and perhaps I'll solve the problem then. Now it's time for a beer.
Geoffrey M Baker


If you have a leak on the inlet side of the pump with a 7 gallon head in the tank you would be seeing fuel leakage at the pipe fittings or along the axis of the pipe. Your nose would also confirm there is a leak.

I would be doing what Dave suggested, disconnecting the connection to your carbies. This will confirm if the pump is operational and you do not have blocked or crimped fuel delivery lines.

Be very wary of using PTFE tape on fittings, never apply it to the first thread of a male fitting and if you undo a connection ensure you remove any residual tape from the threads. Capillaries in the pump and carbies are small and the smallest piece of tape will compromise their operation.
G Evans

Thanks G Evans,

absolutely no leaking on the inlet or outlet side.

I am careful never to wrap ptfe around the first thread as you say, for the reasons you mention.

I'll look at it again tomorrow.
Geoffrey M Baker

Geoffery - regardless of how you wrap the ptfe tape around the threads, that will not fix any leaks that may occur at any of the fittings. All the fittings are 1/4 BSP compression fittings. All the sealing is done between the conical end of the pipe and the mating surface on the male fitting on the pump. All the ptfe tape does for you on these fittings is to create a mess in the threads.

Remove the outlet line from the rear carb and direct it into a jar or can and turn the ignition on and see if you are getting any fuel pump into the can. Also check to see if there is a stream of bubbles along with the fuel. If no fuel is being pumped through or if the fuel stream is full of bubbles, send the pump back to me for testing and, if necessary, warranty repair. Please do not open the the pump yourself as that will void the warranty. Cheers - Dave
D W DuBois

Afraid the situation has compromised any warranty unless David is in a charitable mood. The pump has been dismantled to check the condition of the diaphragm.

Hope the problem lies elsewhere.
G Evans

I second not using Teflon tape. Some years ago I had two new steam traps fail in an autoclave. Fragments of the tape I used were found in the ball/spring seat area so David is sure correct about this. If you remove the inlet pipe and seal with your finger or thumb, I think the pump should stop clicking if all is well with it? If not, a valve problem likely- sticky or debris in it. George
George Butz

Teflon tape is for house hold plumbing...never to be used on automobiles...ever. Regards, tom
tm peterson

I removed the inlet pipe and sealed with thumb... it continued clicking... G Evens, SHHHHHHH!!!
:) Just kidding, if this needs to go to Dave I don't expect warranty coverage. Still hoping I can figure out problem...
Geoffrey M Baker

OK, the pump is working.

I'm not 100% certain what the problem was, but here's my theory.

If you hold up a pump and shake it gently, you should be able to hear the sound of the two brass valves; they should float freely.

I opened the inlet again this morning and once again could find nothing wrong. So I reassembled. Before installing, I noticed I couldn't hear the sound of the valves, and when I opened it up again to figure out why, I saw that the circlip that holds the inlet valve in place had just one of its 'arms' out of the groove and it was pressing inside, against the brass valve itself, and keeping it pressed against its mating surface - in effect, not allowing it to open to allow fuel in. The circlip has four points that should all fit inside the groove in which it should seat.

When I popped the circlip back into the groove, I could hear the valves clacking again, so I reassembled and reinstalled and now it pumped just fine... at twice the pressure of yesterday.

So my theory is that the circlip either was not quite properly in place, or vibrated out of place over time, until the circlip's edge began to ride against the valve, first causing intermittent pumping and then shutting the pump down altogether.

Possibly age has reduced the 'spring' in the circlip so that this can happen more easily - I will see about getting a spare.

But today, it works fine. I took the hose off the inner carb and turned the key and the pump quickly started filling my yoghurt container with gasoline.

So one problem solved, onto another...
The car isn't firing, but that's another issue :)
Geoffrey M Baker

Geoffery - "So my theory is that the circlip either was not quite properly in place, or vibrated out of place over time,"
Thanks for the wiggle room, but that had to be my fault - I normally check that the keeper has all four corners in the groove - must have missed one this time around.

"Teflon tape is for house hold plumbing...never to be used on automobiles...ever."
You should see the volumes written about it in the nuclear reactor world. The worst part about ptfe tape is that when it has had the threads of the fitting screwed in, the tape becomes nearly transparent and when it gets wet, it disappears from sight almost completely. At all of the Naval facilities, ptfe tape is completely banned. Cheers - Dave

D W DuBois

Dave, I suspect (as I always do, and should) that I am entirely to blame. I know since you've rebuilt the pump I've opened it a couple of times (remember, my fuel tank is in bad shape and is discharging crud continuously into the fuel stream) to check the filter. I probably took it out to check for crud and put it back in, so I'll take the blame for it.
Anyway, the engine is still not running great, but the fuel pump is definitely back to normal! Instead of excessive clicking before finally settling in, there are just a couple of clicks...
So all is well!
I've removed the ptfe tape and brushed the threads clean.

And so now I know of another problem to look for when diagnosing fuel issues... make sure to check the circlip carefully!

It's always good to learn something new.
Geoffrey M Baker

Dave, do you have a part number for the "keeper" and also for the washers from Moss or elsewhere? They don't appear to list them on their website and I'd like to have a set of spares for future reference...
Geoffrey M Baker


Glad you isolated the problem, simple things are set to try us.

Definitely obtain rebuild kits from here,

Individual components might be available.

Interesting observations concerning PTFE Tape, it was used to replace another produce for aircraft breathing oxygen systems during my RAAF years of service because it is totally inert. I have been using it in the pneumatics and gas industry for the last 30 odd years and providing you adhere to the assembly methods I posted it does not create problems.

There are many specific varieties of PTFE Tape for applications other than domestic plumbing.
G Evans

Geoffrey, You have e-mail (forgive the misspelling of your name in the e-mail). Cheers - Dave
D W DuBois

Burlen Fuel Services in the UK can supply the fuel pump keeper clips. Part number AUA840.
Lew Palmer

This thread was discussed between 25/11/2014 and 27/11/2014

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