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MG TD TF 1500 - Fuel pump probelms!

After a pleasant drive on the weekend I started my TF to put it back in the garage only to discover that the fuel pump wouldn't stop ticking when I switched the ignition on. My first thought was a broken diaphragm and I was horrified as I'd just filled the tank!

I left the car for a while longer to figure out what to do next only to discovered that it started OK after it had cooled down some. Leaving the car stand for a while seemed to cure the problem.

Has anyone out there experienced this before?

ps has anyone tried using brake pipe clamps on the rubber hose from the fuel pipe to the pump to avoid having to drain the tank to take the pump off? Is this a reliable way of removing the pump without having to drain the tank?

A R Jones

vapor lock?
not sure what brake pipe clamps are..but to just clamp off a rubber hose would a vise-grip pliers work? regards, tom
tom peterson

"the fuel pump wouldn't stop ticking" ?
"Fast ticking" would be a sign that the pump has run dry. Don't let it do that will burn out.

Do you have a fuel filter in line "before" the pump?
If you do move it to "after" the pump.
If the filter gets clogged/dirty...and pump runs dry for extended period of time it will be toast.
The pumps are fairly robust and will pass small bits with no problems.

I use a clamp to shut my fuel off to work on pump and/or change my filter.
My filter is just beyond the pump at rear wheel well on my TF. Earlier TF.s had pump on the firewall. (like the TD)
David Sheward

It could also be the filter inside the tank that is plugged up,,

Thanks for the quick response. I have an in-line filter under the bonnet/hood before the carbs but if memory serves me correctly, I think there may also be a 'rough/medium rough' wire gauze 'thimble shaped' filter in the pump inlet and also one in the tank outlet.

However, a clogged filter doesn't explain why (to me anyway)the pump works again after cooling down.

Looks like I may have to drain the tank after all to check them out.

This is the sort of clamp I had in mind. Don't know if it'll stop a tank full of fuel from depositing itself on the drive!


A R Jones

AJ - First off A filter between the tank and the pump can cause a SU fuel pump to overheat if the filter becomes clogged, but it will do so because the pump stalls in a current on condition. A clogged inlet to pump will not cause the pump to continue to run without stopping.

Second a SU fuel pump that is running non stop will over heat if left running for a long period of time ( 30 minutes or more). I have to think that Dave S. is thinking of modern day fuel pumps for fuel injected cars where the pump is submerged in the fuel tank.

Now on to your problem - A SU fuel pump only runs continuously for a very few reasons - 1) no fuel in the tank, 2) an air leak on the inlet side of the pump - such as a hole in the fuel line or a loose connection to the inlet fitting of the pump, 3) a split or other hole in the diaphragm, 4) a check valve that is not closing due to debris in the pump, 5) a loose fitting on the outlet of the pump, 6) a loose fitting at the carburetors and 7) a needle valve in the carburetor float bowl that is not closing. Items 3, 5, 6 and 7 would be pretty obvious as fuel would be dribbling onto the ground or pumping in a fair stream onto the ground. Item 2 should produce a wet spot on the line from the tank to the pump.

You say that the problem went away after letting the car sit for a period of time - has the problem reoccurred since then? If it hasn't, then I would suspect some debris under one of the check valves. Try removing the fuel line from the carburetors and directing into a container (preferably a quart jar or larger), turn the ignition on and let the pump run a quart of more of fuel through it to flush out any debris from the pump. You might want check the filter you have between the pump and the carburetors to see if it is collecting any debris. It is has, you are dealing with a tank that has rust or other debris in in (or possibly the fuel line from the tank to the pump). Cheers - Dave

PS. - AJ, unfortunately, there is no magic way of stopping the fuel from running out of the tank when your fuel pump is removed, unless you have a piece of flexible line between the ridged line and the pump (unless you can be very fast with a golf 'T').
Daved DuBois

I have disconnected the fuel line fitting at the pump many times with virtually no spillage of fuel. I always have put a few rags around and loosened the fitting very slowly just in case.
If there is no pressure in the tank and the fitting elevation is above the tank then gravity will prevent gas from spilling.

If you need to open the fitting at the bottom of the tank, then you must drain it.

Or did I miss something in this conversation?

Mort Resnicoff (50 TD-Mobius)

Just this weekend my dad and I installed a 5/16" compression shutoff valve ahead of the pump. We found it on the internet for about $20 delivered, although there were some of a more modern design that could be had for about $15. We had the pump out and sent it off to Dave DuBois who did a terrific job of reconditioning. We are also going to put in a backup pump and in-line filter. We figured that having the valve in place makes working on the fuel system a lot easier, as you're finding now. (And it makes a good theft deterrent device, right DS?)
Safety? Fast?
Scott Ashworth - '54 TF

S. R. Ashworth

Mort - it's a TF with the pump down by the rear wheel arch, I suspect.

Tom Lange
t lange

Thank you Tom.
Mort Resnicoff (50 TD-Mobius)

"We are also going to put in a backup pump and in-line filter."

Scott - make sure that you put the filter on the outlet side of the SU pump and thanks for the good words. Cheers - Dave
Daved DuBois

I am going to put the extra pump and in-line filter into a box with rubber fuel injector lines coming out of both ends that will plumb directly into the outflow fittings of the existing pump. That way, if I need to (or if I am on a trip and someone needs a pump), I will be able to remove the unit and just re-connect the fittings. The point is not to change the geometry of the metal lines so that it can be easily reconnected. That's also a reason to have that shutoff valve in place.
Safety? Fast?
Scott Ashworth - '54 TF
S. R. Ashworth

"I have to think that Dave S. is thinking of modern day fuel pumps for fuel injected cars where the pump is submerged in the fuel tank."

I actually run one of the "new square style" solid state pumps installed in rear wheel well on the TF.
"Ticks" just like the old ones, but if it gets "starved" for gas it will tick very rapidly and then "shut-down" untill it has time to cool.
Learned that a few years ago when the "in-tank" filter became clogged.

When "Grace" was here last summer she had some leaks that would do the same thing.(We replaced the entire fuel line and JB Welded a leak in the was "sucking air")) That one was running dual pumps, but John was burnning them up at an allarming rate. We went to swap a spare in that he had but discovered it had the wrong fittings (at 3am!)and ended up putting one like this on the car.
I run the same on my TR7 so we liberated it for the cause. Pretty sure he said the other Lucas failed but that one was still running when the journey ended in Ames Iowa.

David Sheward

Boy, this sure sounds like vapor-lock to me....
If all else is mechanically clear, then vapor lock, as previously mentioned may be the problem....
Easiest way to overcome it, is give it full choke, get it restarted, and "feather" the gas pedal, and the choke, until it clears up....There is no real cure, on these "T"
cars, unless you build a heat shield, similar to the ones
that are on "B" series cars.
Edward Wesson 52TD

Dave S. - "I actually run one of the "new square style" solid state pumps installed in rear wheel well on the TF."

That is a completely different pump from the SU, that is why I am very careful to specify "SU fuel pump" when talking about the fuel systems. The little square, run all the time, make a lot of noise Facet pumps use a bypass valve in the shuttle to set the output pressure. This bypass valve also causes them to continue running when is a blockage on either the inlet or outlet side of the pump. A SU pump will stall when there is a blockage on either the inlet or outlet side of the pump. It is not a problem if the blockage on the outlet side of the pump (the needle valve produces a blockage when ever the float bowl is full), since a blockage on the outlet side of the pump causes the pump to stall in a current off condition. On the other hand, a blockage on the inlet side of the pump causes the pump to stall in a current on condition. If power is left on to the SU pump in this situation, the pump will overheat in a very short period of time. This overheating, if allowed to continue for a period of time, will burn out the internal swamping resistor, which will cause other problems further downstream. See the article, SU Fuel Pumps, Facts and Myths in the SU Fuel Pump Articles section of my Homepage at: Cheers - Dave D.
Daved DuBois

Not sure how you became "Daved" ...but it works! LOL
Had experance with the old SU ...but not for a long time. (Austin in like 1972)
From what you say ...quite different reactions between the 2 different types.
So maybe the question for AJ would be "what pump" he has?

"There is no real cure, on these "T"
cars, unless you build a heat shield, similar to the ones"
I would have to dissagree with that.
My TF had serious vapor lock problems 13 years ago.
Lots of good advice on this BBS that I followed and I have not had a problem since. (heat shield is one thing I never did). There were a number of things I did do ...but did most at the same time so really hard to pin-point a definative "cure".
IMHO: My top guestaments for my cure would be:
Jet-Hot treatment of exhaust manifold.
Replaced rubber fuel lines with stainless braided.
Correct spacers on intake manifold.
Rebuilt Carbs.
Proper timing set @ elevated RPM's.
Of those I really feel the treated exhaust was the best move. I base this on the fact that my fathers TF had vapor lock problems in 1955 when new when operated at low speed for extended periods.
Dad hated parades, but always was talked into it.
His cure was to pack the carbs with burlap sacks filled with dry ice every July 4th.

David Sheward

"Not sure how you became "Daved""
I'm not either, but things in my registration keep changing periodically.

"From what you say ...quite different reactions between the 2 different types."
Yes, they are completely different animals. and you are right, we need to find out what type of pump AJ has - I thought I saw somewhere that it is a SU but going back through the postings there is nothing that says so.

Edward - Dave S. is correct, a heat shield is only one thing that helps prevent vapor lock in the T series engines and then only slightly. A heat shield will only help if the car is moving. In the T series cars (and also the MGAs) the biggest problem occurs when the car is hot and the engine is shut off. What we are experiencing is heat soak - where the heat from the engine and exhaust manifold soaks into the carburetors and the fuel in the channel between the float bowls and the carburetor jet vaporizes and the pressure of the vapor bubble causes the float to shut off fuel flow through the needle valve. Pulling the mixture knob out, which lowers the jets in the carburetors will disrupt the equilibrium and break up the bubble to get fuel flowing again. Leaving the bonnet propped open when parked on a hot day will eliminate the problem, as will removing the side panels of the bonnet (in the 50s in southern California it was common to see T series MG running around with the side panels removed completely.

For an in depth discussion of this vapor lock/heat soak problem, go to the MGA BBS of this site and look in the archives.

Now I am going to see about changing my name vack to David :-) Cheers - Dave
Daved DuBois

Thanks for all the help guys. It's a standard SU pump for a TF.

1 Hot treatment of exhaust manifold. -Not attempted this seems a bit drastic.
2 Replaced rubber fuel lines with stainless braided.-Done
3 Correct spacers on intake manifold.-Done
4 Rebuilt Carbs.-Done
5 Proper timing set @ elevated RPM's. Hmmmmm, I need to check this AGAIN!

I've not used the car much (weather) since rebuilding about a year ago so I'd be surprised if it had an air leak or a blocked filter from sitting in the garage. Right now I'm thinking vapour lock but I'm not sure how this would keep the pump ticking away trying to pump more fuel if the pump is already full of fuel. I had no performance problems or fuel leaks driving the car on the day which you might expect if the pump was struggling to deliver fuel or the diaphragm was broken so I don't think I need to worry about the pump burning out. I have however been in the habit of propping the bonnet open after a run to let the engine cool down before I put the cover on. I don't think I did that last time I used the car. I will do a little more investigation but the weather is turning for the worse again now.

I like the idea of fitting a shut off valve. I definitely have a gauze filter in the tank outlet and again in the pump inlet. Although I suspect they are clean from what you say I think I will remove the tank filter, fit a valve on the tank outlet and leave the inlet filter on the pump. The filter before the carbs is currently clean, it only covers the fuel line from the pump outlet.


A R Jones

AJ - The only time that a vapor lock is going to cause the problem you are experiencing is after the car has been run on a hot day and then parked for a half an hour or so. This usually doesn't happen this time of the year. The problem really sounds like a check valve in the pump is not sealing properly. I would suggest disconnecting the fuel line at the carburetors and directing it into a quart container, then turn the ignition on and let the pump fill the container while watching for bubbles in the fuel stream. If any exist, then you need to look for a pin hole somewhere between the tank and the pump. If there are no bubbles in the stream of fuel, reconnect the fuel line and again turn the ignition on and see if the problem has gone away (flushed out whatever is holding one of the check valves open). A cracked diaphragm should result in a fuel leak at the pump (around the perimeter of the coil housing and the pump body or fuel issuing forth from the vent hole in the coil housing). You haven't mentioned any fuel being pumped out of the float bowl vent pipes so I have discounted a stuck float, but that would also be something to look for. One final thought - if the pump and diaphragm are old, the diaphragm could have hardened, causing it to short stroke. This is a situation where it just kind of vibrates rapidly, but not having enough travel to pump any fuel - in which case it is time to rebuild the pump. See the articles, Fuel Delivery Troubleshooting Guide and Air Leak Troubleshooting in the SU Fuel Pump Articles section of my Homepage at: Also look at the article, Float Lever Drop Adjustment in the Other Tech Articles section of the Homepage. Cheers - Dave

Dave S. - Please note that I accomplished the name change :-)
David DuBois

You just might have given a clue when you said you had just filled the tank. Doing this can create turbulence in the tank and cause any muck at the bottom to be churned up which then blocks the fine filter attached to the outlet boss. (B&G calls it a main feed adapter).
I had this happen to me after filling up and driving to Silverstone for the annual MG meet, car had to be recovered on a low-loader, very embarrassing!
Next day I found the tank filter was blocked throughout its 2" length with 50 years of accumulated grot- fine rust, sand, fluff, hair, general debris and water in the drained petrol!
I know you have just done a rebuild so if you cleaned the tank out this may not be your problem but it will be fuel starvation somewhere.
R.E. Miller

Thanks very much guys. I've logged all your comments. I'll take the pump off, fit a valve and go through the comments one at a time. I need to figure out how to safely remove and store 10 galls of fuel without spilling it over our tarmac drive/garden. I think I'll wait for the weather (rain/snow forecast next week) to improve to see if I can drive some of it off before I try emptying the tank. Hopefully that won't damage the pump. In any event a new pump will be cheaper to replace than a hole in the drive and will be easier to hide from "her what must be obeyed" who is the gardener in the household!

A R Jones

Er indoors what must be obeyed just solved my fuel storage problem. She says I can store it in her car!

Don't you just hate it when they come up with a good idea!

A R Jones

Had this happen to me many times on a trip when the engine is hot and turned off for a break. Go back in several minutes and car starts maybe but with trouble, I pull the chock out a bit and after a few seconds the engine levels out and is OK. I agree with Edward. Vapor lock
Ellis Carlton

This thread was discussed between 06/03/2013 and 09/03/2013

MG TD TF 1500 index

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