Fuel Pump Question

[Glade]

Once you turn the ignition, does the fuel pump then constantly turn, or only as required?? I have a vague idea that this is controlled by a pressure switch in the pump.

More importantly once you turn the key does the fuel pump have a constant power supply to it?

(this is specifically for a 1998 Clio Mk1 Ph3 1.2 D7F 'diet' engine but general adivce is good too!)

Edited by Glade on Friday 5th October 13:08

[stevieturbo]

It will prime for a few seconds initially.

But generally, unless the engine is turning, the pump will be off.

[GreenV8S]

stevieturbo said:

But generally, unless the engine is turning, the pump will be off.

I think most cars these days will do that as a safety measure.

[Glade]

stevieturbo said:

It will prime for a few seconds initially.

But generally, unless the engine is turning, the pump will be off.

Cheers,

Does the fuel pump have a permenant live feed once the ignition is on. Then the fuel pump turns itself on and off using a fuel pressure switch... or does the ECU tell the fuel pump when to operate?

(My remote central locking is shafted and the fuel pump won't operate unless the car is unlocked using the remote. I want to put a wire from a switched live, to the fuel pump relay (fia the fuel cut-out switch) so that it gets switched on by the ignition rather than the central locking/ECU)

Edited by Glade on Friday 5th October 15:05

[Glade]

I have done some research.

If it is a "flow and return" system the fuel pump is always on, pressure is controlled by the fuel regulator, excess fuel is returned to the tank.

If it is a 'returnless' system then the ECU tells the pump the demmand and it pumps accordingly.

Because the car is 1998 french poverty spec I'm guessing it'll be the more basic system. I'm going to stick a multimeter on the fuel pump and see when it has power, and go from there.

[GreenV8S]

Glade said:

If it is a "flow and return" system the fuel pump is always on, pressure is controlled by the fuel regulator, excess fuel is returned to the tank.

If it is a 'returnless' system then the ECU tells the pump the demand and it pumps accordingly.

Both of those are only applicable while the engine is running, though. In both cases, the pump would be switched off when the engine is stopped. It's only very old carbed systems that would have a permanently live pump.

Edited by GreenV8S on Friday 5th October 16:19

[That Daddy]

GreenV8S said:

Glade said:

If it is a "flow and return" system the fuel pump is always on, pressure is controlled by the fuel regulator, excess fuel is returned to the tank.

If it is a 'returnless' system then the ECU tells the pump the demand and it pumps accordingly.

Both of those are only applicable while the engine is running, though. In both cases, the pump would be switched off when the engine is stopped. It's only very old carbed systems that would have a permanently live pump.

Edited by GreenV8S on Friday 5th October 16:19

Showing yer age,Peter

[GreenV8S]

That Daddy said:

Showing yer age,Peter

I spent ages trying to get my engine to fire up on the hotwire system when I installed the blower and I was imagining all sorts of catastrophic problems. Late evening I unplugged the injectors and stuck an old SU onto the air intake. It started first turn of the key and idled and revved cleanly. That same carb has been used with no changes whatsoever on half a dozen engines from 3.5 NA up to 5.2 supercharged and it simply works. Carbs are great! Why isn't EFI that simple?

[leorest]

That Daddy said:

GreenV8S said:

Glade said:

If it is a "flow and return" system the fuel pump is always on, pressure is controlled by the fuel regulator, excess fuel is returned to the tank.

If it is a 'returnless' system then the ECU tells the pump the demand and it pumps accordingly.

Both of those are only applicable while the engine is running, though. In both cases, the pump would be switched off when the engine is stopped. It's only very old carbed systems that would have a permanently live pump.

Edited by GreenV8S on Friday 5th October 16:19

Showing yer age,Peter

My carbed engines had engine driven pumps. How's that for showing your age!

[stevieturbo]

Glade said:

I have done some research.

If it is a "flow and return" system the fuel pump is always on, pressure is controlled by the fuel regulator, excess fuel is returned to the tank.

If it is a 'returnless' system then the ECU tells the pump the demmand and it pumps accordingly.

Because the car is 1998 french poverty spec I'm guessing it'll be the more basic system. I'm going to stick a multimeter on the fuel pump and see when it has power, and go from there.

Not sure where you are getting your research from, because you are wrong.

ALL modern efi systems run as I described in my first post.

[Glade]

stevieturbo said:

Glade said:

I have done some research.

If it is a "flow and return" system the fuel pump is always on, pressure is controlled by the fuel regulator, excess fuel is returned to the tank.

If it is a 'returnless' system then the ECU tells the pump the demmand and it pumps accordingly.

Because the car is 1998 french poverty spec I'm guessing it'll be the more basic system. I'm going to stick a multimeter on the fuel pump and see when it has power, and go from there.

Not sure where you are getting your research from, because you are wrong.

ALL modern efi systems run as I described in my first post.

Yeah, don't think i worded that very well. The clio has a flow and return system but the motor doesn't get power unless the engine is on, and the immobiliser is disabled.

Anyway its irrelavent now because the immobiliser doesn't just cut the fuel pump as i hoped, it disables the injectors too by the looks of things.

Just going to have to hope that the central locking reciever (located by the interior light) doesn't get too badly damaged by the leaky sunroof (a common fault) and leave me stranded At the moment its stuck behind the sunvisor and is starting to get on my tits.

Edited by Glade on Friday 5th October 19:55

[stevieturbo]

Simple rule....

Never buy a french car

[That Daddy]

Some very late EFI systems dont run flow and return systems,flow in one direction only(no return on the fuel rail),they also have injectors mounted in plastic manifolds so obviously fuel perculation is not a worry,not convinced of any benefits though,cant say i have given it much thought eitherand yes Peter i agree you cant knock the old carb atleast you knew where you stood,hell of alot easier to set/up.

[GreenV8S]

That Daddy said:

not convinced of any benefits though

Cost is the only significant benefit I think - you halve the amount of fuel pipe.

[Glade]

GreenV8S said:

That Daddy said:

not convinced of any benefits though

Cost is the only significant benefit I think - you halve the amount of fuel pipe.

I think that with a returnless system, the load on the fuel pump will be less (on average) giving it a longer life.

With a fuel return & regulator the fuel pump is always on at the same [high] level. The pressure is controlled by the regulator rather than the ecu varying (sp?) the load on the pump as in a returnless system. of course i could be wrong.

Stevie: car was free so can't complain. daily hack for the winter. cheap motoring makes it worth it!!

The turd:

[stevieturbo]

Glade said:

I think that with a returnless system, the load on the fuel pump will be less (on average) giving it a longer life.

With a fuel return & regulator the fuel pump is always on at the same [high] level. The pressure is controlled by the regulator rather than the ecu varying (sp?) the load on the pump as in a returnless system. of course i could be wrong.

Regulator is in the tank. So it will make no difference to pump life whatsoever. Its still pumping the same pressures all the time.

Only difference is manufacturing costs to assemble a conventional return style fuel system, when it probably isnt needed.

[dilbert]

I agree with ST, and others.

The way it should work in all cases is that the fuel pump is powered up when you turn the ignition, to the on position. The ECU detects the engine speed, and once beyond a given threshold (somewhere between 0 and idle speed) the ECU overrides control from the ignition switch. The ECU then powers down the fuel pump when the reported engine speed is zero for an arbitary period of time (probably in the region of half a second).

The important distinction here is that if you stall the engine, then the fuel pump stops until such time as you switch the ignition off and back on again.

People do modify this functionality for a variety of reasons, but in general the behaviour above is simple to implement, easy to use, and notably..... Safe!

Edited by dilbert on Saturday 6th October 13:06

[GreenV8S]

dilbert said:

The way it should work in all cases is that the fuel pump is powered up when you turn the ignition, to the on position. The ECU detects the engine speed, and once beyond a given threshold (somewhere between 0 and idle speed) the ECU overrides control from the ignition switch. The ECU then powers down the fuel pump when the reported engine speed is zero for an arbitary period of time (probably in the region of half a second).

The important distinction here is that if you stall the engine, then the fuel pump stops until such time as you switch the ignition off and back on again.

That's one algorithm but certainly not the only one in use.

[Glade]

stevieturbo said:

Glade said:

I think that with a returnless system, the load on the fuel pump will be less (on average) giving it a longer life.

With a fuel return & regulator the fuel pump is always on at the same [high] level. The pressure is controlled by the regulator rather than the ecu varying (sp?) the load on the pump as in a returnless system. of course i could be wrong.

Regulator is in the tank. So it will make no difference to pump life whatsoever. Its still pumping the same pressures all the time.

Only difference is manufacturing costs to assemble a conventional return style fuel system, when it probably isnt needed.

On old systems with a return the regulator is by the engine, a mechanical device that varies the fuel pressure using a vaccum taken from the manifold. The fuel pump could be pumping away like crazy.

I can't find the article i was reading that mentioned pump life as a benefit now... typical.

http://autospeed.com/cms/A_2636/article.html

[quote]In conventional systems, the fuel pressure regulator uses a diaphragm that’s backed by a spring and an intake manifold connection. This causes fuel pressure to vary with manifold pressure – in other words, when there is a strong vacuum in the manifold (eg at light load cruise) the fuel pressure is lower than at wide open throttle, when manifold vacuum is less.

[dilbert]

GreenV8S said:

dilbert said:

The way it should work in all cases is that the fuel pump is powered up when you turn the ignition, to the on position. The ECU detects the engine speed, and once beyond a given threshold (somewhere between 0 and idle speed) the ECU overrides control from the ignition switch. The ECU then powers down the fuel pump when the reported engine speed is zero for an arbitary period of time (probably in the region of half a second).

The important distinction here is that if you stall the engine, then the fuel pump stops until such time as you switch the ignition off and back on again.

That's one algorithm but certainly not the only one in use.

Yep, it's not the way mine works either. With me the car was a bit unreliable when the ECU had control over the fuel pump so I took it out of the equation. Not so safe, but at least it works now. Fortunately I already carry an extinguisher!