Fuel pump

Paulj65

Paulj65

Member
Hi to all and a merry Christmas
im struggling with the fuel system on this p6 3500s it had been changed to an electric pump with a regulator which leaked petrol everywhere !
so I renewed said pump with a new one, tidied up all the pipe work and all seemed well, although I am worried that theres no fuel return,
meaning the pump runs continuously, which has now showed its hand with the ignition on but the engine not running it overfills the carbs resulting in another leak.
im not entirely happy with this so the request is,can someone please send me a picture if possible of the fuel return pipe connection’s and a mechanical pump
im thinking the best thing is to go back to the original hope some one can help
regards Paul
 
Sounds like the pump is producing too much pressure. SU’s (along with most carbs) run at about 3psi. Do you know what pressure the new pump is rated at?
 
Hi
I’m sure it is probably running too high a pressure
I’m worry about the fact this pump runs all the time
whereas the mechanical pump stops when the engine stops
which seems a better situation
so I’m feeling the old route would be best but thanks for the advice regards paul
 
Hi Paul,

With the spill return in situ, the electric pumps are supposed to work continuously, but without it, they must be of the stop-start variety, with continual monitoring of the fuel level within the carburettors.
I'll post a couple of photos illustrating the location of the spill return and mechanical fuel pump. You will have a blankiing plate on your engine in place of the mechanical pump.

Ron
 
SydneyRoverP6B said:
Hi Paul,

With the spill return in situ, the electric pumps are supposed to work continuously, but without it, they must be of the stop-start variety, with continual monitoring of the fuel level within the carburettors.
I'll post a couple of photos illustrating the location of the spill return and mechanical fuel pump. You will have a blankiing plate on your engine in place of the mechanical pump.

Ron
Click to expand...
Thanks Ron appreciate it regards paul
 
Mine had a mechanical pump which I replaced with a front mounted Huco. At switch on it runs for a few seconds and stops. Pretty sure I have a return line - smaller dia than the supply pipes.
 
The carburettor float height is supposed to prevent the carbs overflowing (when set right). Electric pumps generally adjust fuel pressure automatically as a function of flow resistance. You need to adjust your float height first then retune the carb as the fuel level in the float bowl matches the fuel height in the jet....

Given your car had a pressure regulator I suspect the float height was never adjusted properly and the regulator used to compensate...

To adjust float height you bend the tab that contacts the needle (some varieties of which are spring loaded - so check the spring hasn't gone soft/busted if it has them). You can buy needle and seat sets as a kit for not much (you change both together)

Note that electric pumps can vapor lock if not placed below the tank bottom (height) which may also be why the pump and float heights were changed in the first place and the return line removed.
M
 
Mike said "Electric pumps generally adjust fuel pressure automatically as a function of flow resistance. ". First I have heard of this capability. Aside from EFI pumps which usually have an external pressure regulator in the injection system, an oscillating plunger pump (eg the old SUs, or a mehanical) will produce a pressure determined by the internal spring. If this is high enough to overcome the float bowl needle, then you will see flooding. Some of the very latest EFI systems use pumps that have the pressure controlled internally, or even by the ECU. I have seen the same electric pump produce either 35 or 75 psi , as determined by an external regulator, which returns excess fuel to the tank.
 
Pipe coming up from the right is fuel into off side carb from near side carb; smaller dia pipe coming forward bends down and goes back down beside the bellhousing - This is what I think is the return line.
rmpLfH9.jpg
 
Thanks
mine is missing that altogether!??
I’ll need to check further as where it goes and get one made up
thanks for the picture
regards paul
 
I have fitted a Facet electric pump, and was advised by Facet dealer, to fit pressure regulator after the pump, to avoid overwhelming the needle valves. As for the return, he said that Facet are designed to run continuously. I have fitted a home made restrictor in the return line; Piece of nylon rod hat is tight fir in the line, with a small hole drilled in it, I think I used 1mm drill. I like to hear the pump run full speed to fill the float chambers, and then slow to a slow 'tick' when they are full. Personal preference.
Note that you should have an impact cut off fitted in the electric line to the pump, so that it shuts off if you have an accident.
Facets come as two sorts of pump;:-
1. Long suck short blow.
2. Short such , long blow.
P6 with pump mounted in engine bay needs type 1.
Final warning: Electric pumps can fail. I have had 3 fail in the last 20 yrs, and when they do you are stuck. Carry a spare? It is your decision.
 
What do you have there ? The small dia pipe goes to the tank and feeds back into one of the connections at the tank unit, effectively going round in circles.
 
Mine is a Huco in the engine bay. Model 133010 is made for this location, does not need a regulator, and works fine for me - audible for a few secs at switch on, then silent.
 
Hi
thanks all this information is really helpful,
does any one know why the mechanical pump is avoided ?
thanks Paul
 
1. Vapor lock issues in warmer climates and
2. If the car runs out of fuel and stops you flatten the battery trying to get enough fuel to prime the reserve pipe...as its driven off the cam so one pump every two engine turns..
 
Paulj65 said:
Hi
I’m sure it is probably running too high a pressure
I’m worry about the fact this pump runs all the time
whereas the mechanical pump stops when the engine stops
which seems a better situation
so I’m feeling the old route would be best but thanks for the advice regards paul
Click to expand...
The pump will stay on the whole time if it’s pushing fuel past the float valves. So high pressure can cause it to run continuously as it dumps fuel out of the carbs. Before you consider running a return line etc you might want to look at a fuel pressure regulator.

As for it running with the engine off. Do you mean it runs with the ignition off? That’s a problem in It’s own right.
 
If you have an electric pump in the engine bay, swapping a failed pump out would be very easy - MUCH easier than a mechanical unit. They all fail sooner or later.
 
jp928 said:
If you have an electric pump in the engine bay, swapping a failed pump out would be very easy - MUCH easier than a mechanical unit. They all fail sooner or later.
Click to expand...

Some had their electric pump mounted in the axle well under the rear of the car.
 
If you want to keep the fuel reserve function, it is much easier to mount the new fuel pump in the engine bay
The P4 series used a fuel pump located mounted near the back axle. (short suck, long blow type) To keep the reserve facility, this needs to be a dual input single output pump. When I looked some time ago, this type was 'NLA.'
 
sdibbers said:
The pump will stay on the whole time if it’s pushing fuel past the float valves. So high pressure can cause it to run continuously as it dumps fuel out of the carbs. Before you consider running a return line etc you might want to look at a fuel pressure regulator.

As for it running with the engine off. Do you mean it runs with the ignition off? That’s a problem in It’s own right.
Sorry what I mean is the pump runs with the ignition on but without the engine running its this im not happy about I’m pretty sure I’m heading back to a mechanical pump with a return line to the fuel tank thanks for the input it all helps regards merry Christmas paul
Click to expand...
 
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