Hi ppl,
There seems to be quite a lot in the archives on
removing/deleting FPR’s. Problem is, some say you can remove
the supply reg, and others say the return.
So, which one is it? I would think the return reg is the one
to remove.
I’m in the process of uncluttering the engine bay and would
like an answer to this question.
Merry Christmas.
Gav Fisher–
Newcastle, Australia '82 Daim Sov SIII, '86 XJ-S V12 HE
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
I never seen anything but the supply (right side) one being suggested. When
mine failed (a bit of a story) I removed it and all is well.
Doug Dwyer
Longview Washington USA
1995 XJR
1988 XJS V12 Coupe
There seems to be quite a lot in the archives on
removing/deleting FPR’s. Problem is, some say you can remove
the supply reg, and others say the return.
So, which one is it? I would think the return reg is the one
to remove.
// please trim quoted text to context onlyFrom: “Gav Fisher” xjnut@tpg.com.au
I would assume that the B Bank (Left) regulator on the return side is
necessary to maintain the specified pressure in the rail, and only
opens to return fuel to the tank when that pressure is exceeded. I
don’t understand the function of the A Bank (Right) FPR, unless it
somehow acts as a check valve to prevent loss of pressure from the rail
back to the tank after shutdown.
Does anyone know precisely what each FPR is designed to do?
George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: xjnut@tpg.com.au
To: xj-s@jag-lovers.org
Sent: Sat, 23 Dec 2006 10:42 PM
Subject: [xj-s] Fuel Pressure Regulator Removal Question
There seems to be quite a lot in the archives on
removing/deleting FPR’s. Problem is, some say you can remove
the supply reg, and others say the return.
So, which one is it? I would think the return reg is the one
to remove.
Check out the new AOL. Most comprehensive set of free safety and
security tools, free access to millions of high-quality videos from
across the web, free AOL Mail and more.
// please trim quoted text to context only
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
4
Gav Fisher wrote:
There seems to be quite a lot in the archives on
removing/deleting FPR’s. Problem is, some say you can remove
the supply reg, and others say the return.
So, which one is it? I would think the return reg is the one
to remove.
You’d be wrong. It’s the supply reg that gets removed. And I don’t
recall anybody ever suggesting otherwise.
In reply to a message from Kirbert sent Sun 24 Dec 2006:
If you remove the return regulator the pressure in the fuel line
after the supply regulator will effectively go to zero gauge
pressure, the injectors will not function. The return regulator
controls the pressure between the return regulator and the inlet
regulator. If the inlet regulator is removed the pressure across
the fuel rail will vary more with fuel demand. Low demand will
raise the pressure above normal throughout the fuel rail. The
inlet regulator maintains a constant supply of high pressure fuel
for the rail and removing it puts that high pressure into the
rail. It probably causes better performance at a reduced fuel
economy and the higher pressure may keep the injectors cleaner or
it might cause increased erosive wear.
This change was made to help prevent vaporization of
hot fuel. Turns out it was not the FI system design
but poor quality fuel. Fuel did not become high
quality until the '90s when “tier 4” grade became
available and guaranteed fuel caused a fuel quality
war at the pumps that we are still enjoying.
The fuel pump outlet to the engine has a check valve
to maintain pressure from the pump on. The inlet
fuel pressure regulator maintains pressure from the
rail inlet to the pump (remember you need two check
valves to hold pressure at both ends of the tube
holding fuel). The outlet fuel pressure regulator
maintains fuel pressure from the outlet of the rail to
the inlet pressure regulator or pump if no inlet
regulator is there. Each injector also has a check
valve to prevent fuel bleed, which is why you need at
least 25 PSI (or so) to inject fuel, requiring a check
with a gauge rather than opening a line and watching
the spray.
The return from the rail outlet fuel pressure
regulator to the tank is not held under pressure.
The factory did not know if the pump was bleeding fuel
off allowing vaporization of fuel and the hot start
problem, or if the length of pipe by the exhaust was
the problem. By dividing the system with the inlet
fuel pressure regulator they might be able to
determine the failure point. Also, they might make
the rail portion so small as to quickly purge the air
or be able to better hold pressure preventing
vaporization.
What a problem that was for owners and service people.
Spend $50K plus on a new car and then have it not
start after lunch with friends at a swanky restaurant.
Not good for satisfied customers.
I would assume that the B Bank (Left) regulator on
the return side is
necessary to maintain the specified pressure in the
rail, and only
opens to return fuel to the tank when that pressure
is exceeded. I
don’t understand the function of the A Bank (Right)
FPR, unless it
somehow acts as a check valve to prevent loss of
pressure from the rail
back to the tank after shutdown.
Does anyone know precisely what each FPR is designed
to do?
There seems to be quite a lot in the archives on
removing/deleting FPR’s. Problem is, some say you can remove
the supply reg, and others say the return.
So, which one is it? I would think the return reg is the one
to remove.
You’d be wrong. It’s the supply reg that gets removed. And I don’t
recall anybody ever suggesting otherwise.
Logically, the supply regulator ensures you don’t have too much pressure,
and the return regulator ensures that you have enough. The latter goal is
of course the more important one, especially when one considers that the
return regulator can also of course let by excess pressure (since the fuel
system is a loop, and fuel is returned to the petrol tank), so it also
serves the same function as the supply side. If the pressure is too high
(and a properly functioning fuel pump can produce quite a bit of pressure),
your injectors would inject more petrol than they should, which would
result both in rich running and less importantly, a woefully inaccurate
trip computer (which operates on the assumption that a given duration pulse
on an injector = ‘x’ amount of fuel flow).
The return side regulator is also an integral part of the hot start
anti-vapor lock mechanism (when there’s a thermal vacuum valve on the
B-bank side of the fuel rail). The later Marelli-ignitioned cars used,
IIRC, an electrical vacuum switch with a sensor mounted towards the rear of
the A bank side fuel rail (from memory, and I got up about 3 hours earlier
than intended this morning because of a pager call I had to attend to, so
I’m running on 4 hours of sleep).
What precisely is the goal of deleting a fuel pressure regulator? To avoid
having to pay to replace the part, or an attempt to simplify the plumbing
in the engine compartment?
What precisely is the goal of deleting a fuel pressure regulator?
To avoid having to pay to replace the part, or an attempt to
simplify the plumbing in the engine compartment?
IMHO I see no valid reason for the first regulator. I don’t buy the
argument that it controls the inlet pressure.
The second regulator is the one that’s important, for maintaining the
correct fuel rail pressure while the engine is running, and
maintaining that pressure for hot start capability after shutdown.
If that first regulator was all that important all FI cars would have
them.
Bernard, you are correct. As I stated in another post
the first regulator was to divide the system and
controls the pressure in the line leading to the fuel
rail and preventing fuel pressure bleed from the rail.
There was a lot of talk among the people at Jaguar and
the dealers as to what the problem was and the
solution needed to prevent well to do owners from
becoming embarrassed. High heat under the hood, but
now I wonder if it was higher than anyone elses,
pressure bleeding, heating the fuel in the tank making
the incoming fuel to the rail hotter and hotter.
New car sales were made at parties, on the golf
course, over lunch, etc. Talking about how your car
would not start did not make for a saleable car.
IMHO I see no valid reason for the first regulator.
I don’t buy the
argument that it controls the inlet pressure.
The second regulator is the one that’s important,
for maintaining the
correct fuel rail pressure while the engine is
running, and
maintaining that pressure for hot start capability
after shutdown.
If that first regulator was all that important all
FI cars would have them.
For me it was a case where it failed, so I removed it. I intended to replace
it but haven’t quite gotten around to it…and there certainly isn’t a
pressing need to spur me onward.
A new one is only $70 or so as I recall, and its absence can hardly be
noticed what with all the other clutter
Doug Dwyer
Longview Washington USA
1995 XJR
1988 XJS V12 Coupe
What precisely is the goal of deleting a fuel pressure regulator? To
avoid having to pay to replace the part, or an attempt to simplify the
plumbing in the engine compartment?
IMHO I see no valid reason for the first regulator. I don’t buy the
argument that it controls the inlet pressure.
You are absolutely correct on this point.
The second regulator is the one that’s important, for
maintaining the
correct fuel rail pressure while the engine is running,
And probably on this point.
and
maintaining that pressure for hot start capability after shutdown.
I’m not so sure you are right here.
If that first regulator was all that important all FI cars
would have
them.
Here you make a big leap. There are lots of examples on the road
of something that works OK, fewer that work really well. If I
take your assertion I could as well say there should be no
cars with a more expensive feature Y because feature X works
well enough that any improvements due to Y offers. All of us
can probably think of counter examples.
I believe the importance of the first regulator (on the HE) is
basically what George has said: it allows the second one to do a
better
job of controlling the rail pressure. Without a first regulator the
second is fighting to keep rail pressure constant, as fuel flow is
varying,
when the pump pressure tends to vary tremendously with varying flow.
The latter is true because it is a constant volume type of pump,
meaning
it tends to produce the same flow regardless of the flow resistance
it is delivering to (i.e., a more or less vertical head-flow curve).
The first regulator, as George says, maintains the
pressure between the pump and the rail more or less constant. Thus the
flow system downstream of the first regulator behaves more like a
constant pressure supply rather than a constant volume supply, and the
second regulator just has to trim, so to speak.
So, with the inlet regulator removed, this deficiency is manifested…how ?
Asking, not arguing.
Cheers
Doug Dwyer
Longview Washington USA
1995 XJR
1988 XJS V12 Coupe
I believe the importance of the first regulator (on the HE) is
basically what George has said: it allows the second one to do a
better job of controlling the rail pressure.
The first regulator, as George says, maintains the
pressure between the pump and the rail more or less constant. Thus the
flow system downstream of the first regulator behaves more like a
constant pressure supply rather than a constant volume supply, and the
second regulator just has to trim, so to speak.
In reply to a message from Doug Dwyer sent Tue 26 Dec 2006:
The return regulator releases the pressure at a predetermined set
point in a very specific way (or pressure curve, based on the
design of the regulator) and is designed to be open all the time,
much like a throttle valve. The inlet regulator acts the same way
but probably at a slightly higher set point. When you place one in
front of the other the pressure between the two is maintained in
that specified range. If you are now designing injectors that open
based on duration and since you now have a narrow range of pressure
behind the injectors, you can accurately calculate the amount of
fuel delivered for a specified opening duration for the first and
the last injectors on the rail.
If you remove the inlet regulator the high pressure flows into the
rail and the outlet regulator opens more to relieve the pressure.
If the regulator were perfect it would maintain the rail pressure
at exactly the design setpoint, but primarily due to the fact that
it was designed to hold a specified pressure at a lower flow, it
will not be able to maintain the exact same pressure at this new
higher flow rate. Further, pumps force fluid in discrete pulses
which cause the regulator to oscillate, complicating the pressure
control. Leaving the inlet regulator in the loop dampens the
pulsing, reduces the flow to the outlet regulator (and also the
flow through the entire loop), and raises the pressure between the
pump and the inlet regulator. All by adding a pressure drop in the
system. So if you are the designer of the regulators and you
designed them to work in tandem, removing one does change the
system even though it may not shut down the engine.
The result is inaccurate fuel delivery at all speeds, higher flow
through the system, and if the fuel was vaporizing in the line at
the lower pressure it will prevent vaporization between the pump
and the inlet regulator.–
The original message included these comments:
So, with the inlet regulator removed, this deficiency is manifested…how ?
If George and I are correct removing the inlet regulator will
result in wider swings (but probably still small) in rail pressure
as fuel flow rate changes. Now, whether rail pressure swings
result in noticeable changes in operability,
I don’t know. Since so many on these lists have removed them
without complaint, I assume they don’t. But, there may also
result in worse fuel economy and/or emissions, neither of which
would be noticeable to the driver.
One other effect of the first regulator is raising the pressure in
the supply line between it and the pump. If removed, that
pressure will be rail pressure, somewhat lower. That would
increase the chances of vaporization if the line is too close to the
exhaust at any point. Does it happen? I guess those who have made the
change will have to tell us.
I guess my comments were speculation on why the regulator was put
there in the first place, rather than predicting dire consequence of
removal.
Also, I am assuming the first regulator is like the second, i.e.,
acting to control upstream pressure by opening when that pressure gets
higher than the set point. If it is in fact a reverse acting
regulator, none of what I’ve said is true. (It might not be anyway!)
In reply to a message from Ed Sowell sent Tue 26 Dec 2006:
Hey folks lets use some logic here. IF the inlet reg. was important
then WHY did Jaguar remove it on the later cars???
The inlet reg. is a hold over, a not needed piece, just something
to fail one day.
Like someone else point out, if the thing was really needed then
all FI cars would have it.
In reply to a message from Dr. Chadbourn Bolles sent Tue 26 Dec 2006:
Using that logic I suppose you could eliminate all carburetors on
older model cars. Could it be that at the time the system was
designed there was a need for the regulator but later, just like
the carburetor, they devised a way to do without the inlet
regulator. Maybe, and I don�t want to get to far fetched, maybe
the newer pumps were better regulated, who knows. The one thing I
do know is that it is very unlikely the engineers put it there for
the purpose of frustrating us years later. Its even more doubtful
that it was put there for some aesthetic reason. It may seem like
overkill but it also may perform a function that you don�t yet know.–
The original message included these comments:
Hey folks lets use some logic here. IF the inlet reg. was important
then WHY did Jaguar remove it on the later cars???
Actually, I was NOT pretending to know what the first/A Bank FPR does.
I was only guessing that it acts as a check valve to maintain fuel rail
pressure after shutdown, to improve hot starts by preventing fuel
vaporization in the rail.
If you look at each FPR, you will see that fuel flows FROM the fitting
on the side, TO the fitting at the rear, in each instance. It flows
from the fuel pump into the side of the A Bank FPR and through the rear
fitting to the fuel rail. Fuel flows from the left fuel rail to the
side fitting of the B Bank FPR, and through the rear FPR fitting to the
tank return line.
I fail to see how the A Bank FPR can act like a damper or modulator to
affect inlet pressure at the rail. My guess would be that it opens at a
lower pressure than the B Bank FPR. The two FPR’s DO have different
part numbers and have different rear fittings according to the Parts
Catalogue.
And the B Bank FPR should NOT be always open to some degree as someone
suggested, or there will be no maintenance of rail pressure after
shutdown. It is a spring-operated (vacuum modulated) valve that doesn’t
open until rail pressure is attained.
George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: EdsJag_12@efsowell.us
To: xj-s@jag-lovers.org
Sent: Tue, 26 Dec 2006 11:05 AM
Subject: RE: [xj-s] Fuel Pressure Regulator Removal Question
Doug,
If George and I are correct removing the inlet regulator will
result in wider swings (but probably still small) in rail pressure
as fuel flow rate changes.
Check out the new AOL. Most comprehensive set of free safety and
security tools, free access to millions of high-quality videos from
across the web, free AOL Mail and more.
Hey folks lets use some logic here. IF the inlet reg. was important
then WHY did Jaguar remove it on the later cars???
Different design.
The inlet reg. is a hold over, a not needed piece, just something
to fail one day.
Like someone else point out, if the thing was really needed then
all FI cars would have it.
How far can I go with this idea, Chad? I mean, if the car runs without
it, or better yet if any car will run without it, throw it out.