dodgy fuel pump

[Matt Tomkins]

hi all,

My fuel pump constantly ticks when the ignition is turned on, and doesn't stop.
i have an in-line fuel filter fitted, and it doesn't fill up even when the pump is ticking away - i fear it may be an issue with the diaphragm being perforated - does this sound likely?

I would probably fix this one, but - as the car runs okay as it stands - i wouldn't like to poke around until a replacement is fitted and working.
- i can't afford a new one from the normal suppliers, but was looking on ebay for one in good working order.
- would any single su pump work, or is there a specific one to go for?
would this one be the same as is on at the moment?
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 500wt_1156

Cheers,

as always the advise is much appreciated,

Matt

[Dean]

Have you tried taking off your petrol cap? There could be an air lock in the tank.

[Matt Tomkins]

yeh - topped it up a couple of times since it's been back on the road :/

[Dean]

I think we need to eliminate a blocked fuel pipe from the tank and make sure it is the pump first.

You could always disconnect the pipe coming in from the tank... put a rag over the top to stop any petrol going everywhere, turn on the ignition and feel the inlet pipe to the pump and see if it is sucking.

If you have a compressor you could gently blow down the fuel pipe (rag wrapped around top of pipe and goggles) to try and clear it.

Don't disconnect the outlet pipe from the pump and turn the ignition on incase the pump is working and sprays petrol everywhere. It will keep pumping loads of petrol until you turn off.

[Matt Tomkins]

i will try that - where should i connect the compressor?

also, i found this one which looks like a bargain - will it work?

[Dean]

Have you got a small blowing attachment gun for the compressor, that you can use to blow fine air to clear work benches etc?

If you blow down the steel pipe that comes from under the car that attaches to the pump.... after unscrewing it from the pump. There may be some crud that has found it's way from the tank up the pipe. This would simply blow it back into the tank. Only do it gently though... not huge blasts of air!!! You don't want the contents of the tank getting blown around.

[Dean]

the little blow gun in the picture is what I mean.


http://www.machinemart.co.uk/shop/produ ... ir-brushes

[bmcecosse]

Get rid of the filter (especially if it's on the inlet side) - you don't need it. Then check if the float bowl is overflowing into the carb (remove the bell and look down at the jet with the ignition ON) - the level may be set too high. The MGB pump will sell for MUCH more - and it's a 'pusher' pump - Minor needs a 'puller'.

[Neil MG]

Does the SU electronic pump constantly tick? I know some of the other manufacturer's pumps do.

[Matt Tomkins]

Have you got a small blowing attachment gun for the compressor, that you can use to blow fine air to clear work benches etc?

i havn't, and my compressor is one for a small airbrush - i'll try and rig something up!

Get rid of the filter (especially if it's on the inlet side) - you don't need it.

i was worried about getting s**t in the carburetor from the bottom of the tank
a local classic car specialist garage fitted one to my dad's MG midget as he had exactly this problem and the float chamber got jammed up - spilling petrol from the bleed hole down passed the hot exhaust!

would it be detrimental in anyway to leave it on?

Does the SU electronic pump constantly tick?

mine sure does :p

[bmcecosse]

The pump already has a filter - and the SU carbs can handle dirt just fine....... The extra drag of the filter may be the problem. No reason why an 'electronic' SU fuel pump should tick 'all the time' - it's still a throw-over pump - the electronics just replace the points.....

[Matt Tomkins]

right - i'll buy a new fuel line and fit without a filter asap

i don't know if it'll help, though - as it did constantly tick before the filter was fitted as i remember - but i havn't driven it myself before it was fitted. i can only try!

[bmcecosse]

Well - take the bell off and look inside to see if it's flooding!

[Matt Tomkins]

Well - take the bell off and look inside to see if it's flooding!

what do you mean by the 'bell'
- sorry if i appear clueless :/

[rayofleamington]

Does the SU electronic pump constantly tick? I know some of the other manufacturer's pumps do.

With the ignition on and engine not running they usually tick about once every 8 seconds. With engine at idle it's once ever 2 to 4 seconds.
If it's ticking more frequently than once every 2 seconds with the engine off, then it sounds like there's a problem somewhere.
If it ticks 5 to 10 times a second then you're running on fumes/air!


An inline filter between the pump and carb is not likely to fill with fuel. Normally it will fill up until fuel can trickle from the outlet along the pipe to the carb. Depending on the outlet position, thie filter can be anything from 2/3 full to almost completely empty.
The fuel trickles through the filter and fills up the remaining the pipe to the carb. When the fuel level drops in the carb it allows fuel to enter the float chamber from the pipe. This reduces the pressure in the pipe - which in turn lets the fuel pump click through one more cycle and pressure is restored in the pipe (causing the fuel pump to stop again). The burst of fuel enters the filter but then runs through it and down the pipe to the carb.

[Matt Tomkins]

With the ignition on and engine not running they usually tick about once every 8 seconds.

mine's about every 2 seconds with the engine off

it then stays pretty consistent with this when on tickover, although maybe slightly faster.

i'll leave it be for now i think, as it's working, but have a look when i get a free weekend...
...could be a while! - maybe over summer after exams!