Peugeot intank pump - too much pressure?
 

Having my intank fuel pump (2003 CDTi, 2 pumps) failed more than a year ago and also thanks to the lot of useful information found in this forum, I'm almost going to buy the 1525Y3 Peugeot pump and go through the diy job to replace the dead one in my tank.
The price is about 18O€, not cheap but certainly worth the try, as the Rover spare part is about 43O€ (here in Italy).

Before ordering the pump I had a detailed look at my Rave CD, in which I found two things which seem to be somehow conflicting, regarding the pressure coming from the pump, which is 2.5bar for the Rover one and 3.2bar for the Peugeot.
In the Workshop Manual, under Engine Management Description, I read this:

The intank LP fuel pump draws fuel from a swirl pot and delivers it to a filter unit adapter mounted in the LH section of the fuel tank. The adapter unit contains a pressure regulator which is calibrated to 3.6 bar (52 lbf/in 2 ), this will not open during normal operation of the system.

The 3.2 bars of the Peugeot pump are well under the level at which the pressure regulator opens, suggesting that the pressure difference between the two pumps does not cause any problem or strain at all.

However in the same manual, under Service Procedures - General Data, I found out that the Pressure regulator (fitted between fuel filter and HP injection pump) has a nominal pressure of 2.5 bar.

This means, if I'm not mistaken, that the Peugeot pump makes the low pressure side of the whole circuit work at a pressure (3.2) which is ABOVE the one the HP pump is expecting, thus making the Pressure Regulator near the HP pump work all the time to lower that pressure to the nominal value of 2.5.

Couldn't that put some kind of extra strain on the circuit or on the pressure regulator or, worse, on the HP injection pump? Besides, how does the under bonnet pump "react" while receiving fuel from the tank at a pressure which is pretty higher than the one expected? Does it overdraw that pressure further on?

Anyone knowing if the facelifted 75 has, together with a more powerful intank pump (at which pressure?), some different calibration of the Pressure Regulators?

I am almost certain the later facelift models with no under bonnet pump were fitted with intank pumps rated at 3 bar so I expect the one you plan to use will be ok

Thanks for your answer.
Don't you think that the facelifted single pump models may have some different calibration of the pressure regulator located near the HP injection pump?

I doubt it, otherwise I think by now those people that have fitted the later Peugeot pumps may have mentioned something

the LP sensor on the fuel filter expects to see the pressure rise to 2.5 bar minimum in normal operation from both pumps when you first turn on the ignition

I would not be surprised if with just the one pump in the tank that it may well need to be 3 or 3.2 bar at that end in order to maintain 2.5 bar at the LP sensor taking into account the extra head as well so in theory you could even get rid of the under bonnet pump if you wanted to

I agree with that: a 3.2 bar in-tank pump ALONE could probably be able to deliver and mantain 2.5 bar at the LP sensor which is far away and above, near the fuel filter.

What I wonder about is: what happens when the action of the 3.2 bar in-tank pump gets ADDED to the action of the under bonnet pump? What kind of pressure do we get at the LP sensor? Maybe a too high pressure, capable of putting additional strain to the system and thus causing some possible long term damage to the very expensive and delicate HP pump and valve/sensor circuit?

Any more opinions?

sadly, unless one of the original engineering team remember doing the "2 to single pump" revision, then it is probably going to remain an experiment in action... awaiting posts from those who have gone that route.
It would be interesting to see if anyone has experimented with disabling the front pump temporarily. Surely, if it works fine like this, it may be safer long term (unless the peugeot pump is put under more strain through doing this for some reason)

Good question Jon

Jules posted some pictures of the inards of the front pump it may be that the fuel will flow through unhindered if it is off or it may be quite restrictive.

I think on balance when (if) my in tank pump goes I will go for the higher output pump and remove or bypass the underbonnet one and simply wait to see if anything odd happens but I don't expect any problems

I did have some suspicious pump like symptoms (car cutting out at at high RPM in 2nd and 3rd) when I first bought it but not since I applied a couple of bottles of Millers and it has since done another 20K without repeat. Perhaps at that time I had simply worn through a period of poor brush contact in one of the pumps.

ooh, what a good thread... but we havent come far, have we?

Can anyone develop Keiths thought that "the later (Rover) pump may be 3 bar"?

How does one equate 2.5bar and 3 bar (pressure) to 190lph and 255 lph (flow rate) that Walbro quote me?

from http://www.stealth316.com/2-fuelpumpguide.htm#j8
"Fuel pumps supply fuel volume; they do not create pressure in the fuel lines. In a return-line system (like in the 3000GT and Stealth), the fuel pressure regulator restricts the return fuel flow in order to create pressure in the supply line. As the fuel supply line pressure increases, such as during boost conditions for forced-induction engines, the pump has to work harder (it actually rotates slower and the current draw increases) and so the volume flow decreases. "

So surely its the volume thats important, as the cars pressure regulator will help maintain the required pressure?

The 2.5 bar tank pump delivers 240 litres per hour (shown as 4 LPM) @ 12V according to fuel system data. Am I right in thinking this is calculated based on the specific delivery pipe diameter which may change from pump to pump?

In terms of the later in tank pump the part number is WFX000350. Rimmers and Xpart say they are out of stock with no known date for restock at the moment. Rimmer's say the part number does not come up with any additional information regarding the pressure. 3 bar does ring a bell but this may simply be from reading Keith's posts on the subject. I wonder if it is written on the pump itself?

Just had a look at the fuel system illustrations and it looks as though the sensor on the fuel filter just makes sure there is enough pressure to feed the high pressure pump. After the filter there is a pressure relief valve, which looks to be a physical thing rather than ECU controlled as it doesn't show up on the wiring diagram. This relief valve lets fuel flow into the high pressure pump and relieves excess fuel in a loop back to a point just before the under bonnet pump. There is a second relief valve on the high pressure pump which relieves excess fuel back through the cooling system and back into the tank. This second valve is rigged up to the ECU.

I presume the system which uses the later pump still has this local return loop but it just takes it back to the other side of the filter rather than the other side of the under bonnet pump?

The description states "The extra pump is fitted before the fuel filter and increases the pressure to assist the fuel through any potential blockage of the filter during cold starts. The extra pump helps to ensure all engine
fuelling requirements are satisfied in all conditions."

When the ECU detects too little pressure at the fuel filter sensor it reduces throttle to avoid damage to the high pressure pump, presumably eventually resulting in the failure to start or cutting out when the in tank pump starts to die. It doesn't mention the ECU checking for high pressure at all, I guess this is just dealt with by the mechanical relief valve.

Regardless I imagine that the 3.2 bar Pug pump will run fine without an under bonnet pump as it isn't going to be putting much strain on that relief valve by the time it has got all the way around past the filter but should supply sufficient additional pressure over the 2.5 bar pump to get it through the filter. It sounds as though the second pump was supposed to be a "belt and braces" addition which turned out to be the only thing that kept the car running when the poor quality in tank pump failed.

Not sure if any of that is even useful, I am just "writing out loud" to be honest whilst I try and get my head around how it all works myself. Still managing to avoid doing any actual work today (see earlier thread on my newly found interest in the variable rail track gauges of pre Civil War America. *yawn, snore*