Fuel Pumps - V8s - to Facet or not to Facet?
Discussion
Hello,
My old Indy (4.7 V8) had some fueling problems last year which turned out to be one of the old facet type (I think that's how they are described) fuel pumps - I replaced it with a new one which now runs sweet as. Since then I've not used it that much but ran it down to the GRCC members meeting the other week and only used the tank with that new pump attached - all good - until it got a bit low so I switched to the other tank and (other original) fuel pump - hmmmm, spluttering. There was enough in the first tank to get me home so I swtiched back and thought I'd investigate later. There could be a few things causing it all of which are pretty easy to fix but that isn't my question....
Question is: the Maserati pumps (original and new, pics below) pump all the time, ticking away (obviously only the one which is live) - but I wondered is it really necessary to be constantly pumping? Even if you turn on the ignition without engine running the pump will buzz away all the time. Whereas on my Dart (2.5 V8) the fuel pump must detect the back pressure and stop pumping when the carbs are full. ie. if you turn the ignition on the pump clicks away rapidly, then slows, then ticks every few seconds - it is then that you turn the key and off she goes - I've never had her starve of fuel even on full chat so does the Masser really need a fuel pump that is constantly pushing fuel pressure into the carbs? My P6 (3.5 V8 but very tweaked) is also running a Holley Red facet type pump pumping all the time through a regulator - with the petrol hungry V8s do they need that much fuel pressure?
As you can tell, I really don't understand fuel pressure, durr brain question but surely as long as there is fuel enough to fill the carbs then that's all is needed isn't it?
I'll probably just replace like with like on the Indy if I need to but the Dart pump is just so good (super handy for listening to and understanding if/when there are petrol issues) I wondered why I can't have a similar setup elsewhere.
Cheers
Joe
My old Indy (4.7 V8) had some fueling problems last year which turned out to be one of the old facet type (I think that's how they are described) fuel pumps - I replaced it with a new one which now runs sweet as. Since then I've not used it that much but ran it down to the GRCC members meeting the other week and only used the tank with that new pump attached - all good - until it got a bit low so I switched to the other tank and (other original) fuel pump - hmmmm, spluttering. There was enough in the first tank to get me home so I swtiched back and thought I'd investigate later. There could be a few things causing it all of which are pretty easy to fix but that isn't my question....
Question is: the Maserati pumps (original and new, pics below) pump all the time, ticking away (obviously only the one which is live) - but I wondered is it really necessary to be constantly pumping? Even if you turn on the ignition without engine running the pump will buzz away all the time. Whereas on my Dart (2.5 V8) the fuel pump must detect the back pressure and stop pumping when the carbs are full. ie. if you turn the ignition on the pump clicks away rapidly, then slows, then ticks every few seconds - it is then that you turn the key and off she goes - I've never had her starve of fuel even on full chat so does the Masser really need a fuel pump that is constantly pushing fuel pressure into the carbs? My P6 (3.5 V8 but very tweaked) is also running a Holley Red facet type pump pumping all the time through a regulator - with the petrol hungry V8s do they need that much fuel pressure?
As you can tell, I really don't understand fuel pressure, durr brain question but surely as long as there is fuel enough to fill the carbs then that's all is needed isn't it?
I'll probably just replace like with like on the Indy if I need to but the Dart pump is just so good (super handy for listening to and understanding if/when there are petrol issues) I wondered why I can't have a similar setup elsewhere.
Cheers
Joe
If both the old and new pumps tick along all the time, that would suggest that the Indy has a return fuel line, so that when the carburettor bowls are full rather than blocking the line and causing the fuel pump to stop, it just redirects the flow back to the tank. The SP250 by the sound of it does not, so when the bowl is full, the needle valve closes and the pump stops, or perhaps recirculates internally.
If it had just been the old pump on the Indy that carried on pumping, I'd wonder if the internals of the pump are worn and able to continue pumping against the closed valve and just leak backwards, but as the new one does it too, that sounds unlikely.
I haven't done much with electric fuel pumps, I wonder whether there are different types intended for constant running vs. stop/start. I have a thought that the constant running would be better for the pump, but that's not based on any actual knowledge, it just "seems" right.
I suspect another thing with having a fuel return line rather than just holding the fuel back might be down to temperature. If you've got an engine bay that gets very warm, having fuel sitting in the fuel line while it waits for the bowl level to drop could cause it to get warm and cause fuel starvation in extreme cases. Allowing that unrequired fuel to effectively circulate back to the tank means that when more is required, it won't have been sitting in the line for a while.
(Obviously I'm presuming the Indy has carbs based on what you said earlier, injected systems are different and I believe run at higher pressure and all have return lines. Not sure about that, either.)
If it had just been the old pump on the Indy that carried on pumping, I'd wonder if the internals of the pump are worn and able to continue pumping against the closed valve and just leak backwards, but as the new one does it too, that sounds unlikely.
I haven't done much with electric fuel pumps, I wonder whether there are different types intended for constant running vs. stop/start. I have a thought that the constant running would be better for the pump, but that's not based on any actual knowledge, it just "seems" right.
yosini said:
I've never had her starve of fuel even on full chat so does the Masser really need a fuel pump that is constantly pushing fuel pressure into the carbs? My P6 (3.5 V8 but very tweaked) is also running a Holley Red facet type pump pumping all the time through a regulator - with the petrol hungry V8s do they need that much fuel pressure?
As I understand (and being the internet, there's a chance someone will correct me if I'm wrong) with a carburettor engine, there isn't really a need for high fuel pressure. The fuel pump feeds the carburettor bowl, and the engine runs from that bowl, not from the pump. The issue is how quickly the bowl can re-fill while you're pushing along hard, and how much pressure the cut-off valve can take. I suspect another thing with having a fuel return line rather than just holding the fuel back might be down to temperature. If you've got an engine bay that gets very warm, having fuel sitting in the fuel line while it waits for the bowl level to drop could cause it to get warm and cause fuel starvation in extreme cases. Allowing that unrequired fuel to effectively circulate back to the tank means that when more is required, it won't have been sitting in the line for a while.
(Obviously I'm presuming the Indy has carbs based on what you said earlier, injected systems are different and I believe run at higher pressure and all have return lines. Not sure about that, either.)
Edited by droopsnoot on Wednesday 24th April 10:10
Really just repetition but with a return system there is always the correct pressure feeding the carburettors, whereas an old SU system like the E-type wil tick quickly when you turn the ignition on, then slow down and stop because the foat chambers are full. Same difference really because both maintain the correct pressure. IIRC the E-type runs at 4 lbs pressure whereas a modern common rail injection system is running at over 100 bar!
But your fuel spluttering; I would think that the problem is an accumulation of dirt in the tank and it needs draining and the filter cleaning. Best to do both I feel. Better than sucking the rubbish up into the carbs and grinding to a complete halt.
But your fuel spluttering; I would think that the problem is an accumulation of dirt in the tank and it needs draining and the filter cleaning. Best to do both I feel. Better than sucking the rubbish up into the carbs and grinding to a complete halt.
Yosini,
It's a common practice in competiton, especially rally, to fit two fuel pumps, for reliability through redundancy. One fails, you turn on the other. But you have two fuel tanks with a pump for each. How are the supply lines connected?
A rally car with two pumps often sets them up in parallel, a Y-connector splits the single feed to the pair, and another joins their outputs to a single supply the engine. But it is ESSENTIAL that there are one-way valves downstream of both pumps, before the joining Y, because Facets, and other pumps permit backflow. Without a valve and with any back pressure at all, in this configuration, the working pump would just flow the fuel in a circle, and deliver little to the engine. In fact it's better practice to connect the pumps in series, as the upstream can pump through the downstream, and the downstream draw effectively through the upstream, and no valves or additional hoses and connectors! Simples!
Your car must have a Y-connector somewhere to join the supplies from either pump. Are there one-way valves on the hoses before the Y? If the engine is not consuming fuel, (Ignition on, engine off) then the working pump will, without a one-way valve, just transfer fuel from one tank to the other, and continue running until the working tank was empty!
John
It's a common practice in competiton, especially rally, to fit two fuel pumps, for reliability through redundancy. One fails, you turn on the other. But you have two fuel tanks with a pump for each. How are the supply lines connected?
A rally car with two pumps often sets them up in parallel, a Y-connector splits the single feed to the pair, and another joins their outputs to a single supply the engine. But it is ESSENTIAL that there are one-way valves downstream of both pumps, before the joining Y, because Facets, and other pumps permit backflow. Without a valve and with any back pressure at all, in this configuration, the working pump would just flow the fuel in a circle, and deliver little to the engine. In fact it's better practice to connect the pumps in series, as the upstream can pump through the downstream, and the downstream draw effectively through the upstream, and no valves or additional hoses and connectors! Simples!
Your car must have a Y-connector somewhere to join the supplies from either pump. Are there one-way valves on the hoses before the Y? If the engine is not consuming fuel, (Ignition on, engine off) then the working pump will, without a one-way valve, just transfer fuel from one tank to the other, and continue running until the working tank was empty!
John
Thanks all,
I think I understand it all a lot better now - also makes sense as I changed the tank and all fuel lines in the Dart last year and there was no return pipework. On the Indy there's a connector pipe (see pic) which both pumps flow into so I presume this has a one-way valve system in it to prevent the pumps pumping into each other (and the opposite tank) as you suggest. I've ordered a new facet one and will clean the old one out and keep it as a spare. The only thing I've not got my head around yet is how the return line comes back to the tanks - how does it know which one to flow back into?
Cheers
Joe
I think I understand it all a lot better now - also makes sense as I changed the tank and all fuel lines in the Dart last year and there was no return pipework. On the Indy there's a connector pipe (see pic) which both pumps flow into so I presume this has a one-way valve system in it to prevent the pumps pumping into each other (and the opposite tank) as you suggest. I've ordered a new facet one and will clean the old one out and keep it as a spare. The only thing I've not got my head around yet is how the return line comes back to the tanks - how does it know which one to flow back into?
Cheers
Joe
Yosini,
Your Maserati has a set of Weber caburettors? Carburettors have a "float chamber" that works like the cistern on a loo. The float rises on the top of the fuel in the chamber closes, until it closes a valve that stops more fuel entering. When fuel is used, the level falls slightly, the float falls, the valve opens and so on. The only pressure that affects fuel flow into the engine is the hydrostatic pressure of the height of the fuel in the chamber, which this mechanism keeps constant (plus the vacuum in the inlet ducts).
This is why on your Dart, the pump runs fast to fill the chambers, emptied by ?drainage, ?evaporation, until the level rises and the valve closes.
There is no return hose, as there is on fuel injection models, so any search for that will be in vain.
From your pic, I have no idea if that connector joining the outflow from the pumps includes one-way valves (AKA 'check-valves'), but it looks a bit simple to do so. You must know Maserati specialists who will know if it does or not.
John
Your Maserati has a set of Weber caburettors? Carburettors have a "float chamber" that works like the cistern on a loo. The float rises on the top of the fuel in the chamber closes, until it closes a valve that stops more fuel entering. When fuel is used, the level falls slightly, the float falls, the valve opens and so on. The only pressure that affects fuel flow into the engine is the hydrostatic pressure of the height of the fuel in the chamber, which this mechanism keeps constant (plus the vacuum in the inlet ducts).
This is why on your Dart, the pump runs fast to fill the chambers, emptied by ?drainage, ?evaporation, until the level rises and the valve closes.
There is no return hose, as there is on fuel injection models, so any search for that will be in vain.
From your pic, I have no idea if that connector joining the outflow from the pumps includes one-way valves (AKA 'check-valves'), but it looks a bit simple to do so. You must know Maserati specialists who will know if it does or not.
John
yosini said:
The only thing I've not got my head around yet is how the return line comes back to the tanks - how does it know which one to flow back into?
A very good question. No idea. I am only guessing that there is a return line as a reason for the pumps to run continuously. I know it's more common on injected systems, but variants of my Vauxhall mechanical pump also feature a return line output for some reason. Does this diagram explain anything? You can hover on each part number, but the descriptions are mainly in Italian. https://www.eurospares.co.uk/parts/maserati/indy-4...
Great find, droopsnoot! That doesn't shsow any sort of return line, and the connector where the hoses from the two pumps joins (Item 14) is described merely as a "Union". It's not at all clear, but hose ('manicotto') 27 logically joions to tube 28 and thence to the pressure regulator (50), with no sign of a one-way valve. Hose 32, after the pressure regulator is "to carburettors". (I'm no linguist, but Google Translate helps!)
So pointless searching for a return. Either there is back flow, which a new pump may make worse in the other, worn one, or the old worn pump is chattering away, trying to flow fuel. Replace both, and run both togther, to minimis back flow.
Or fit one ways!
John
So pointless searching for a return. Either there is back flow, which a new pump may make worse in the other, worn one, or the old worn pump is chattering away, trying to flow fuel. Replace both, and run both togther, to minimis back flow.
Or fit one ways!
John
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