[xj40] I'll ask my FF23 question another way

XJ40
1

hello list…a few days ago I posted a question regarding the
possibility of a failing fuel pressure regulator causing a Fuel
Fail 23 code on my VCM…I did not receive any responses so please
let me ask the question another way…can anyone that has had a
FF23 code tell me what they did to correct it?..thanks…–
Cliff - '93 XJ-40 Sovereign (4.0L)
Lancaster/South Carolina, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

2

In reply to a message from Cliff Archie sent Wed 16 Jun 2004:

As you already know , there are several causes of a ‘fuel fail 23’
message. Which indicates a rich mixture. I would go for the water
temp semsor first (although that normally sets a ‘fuel fail 14’)
then I would go for the Lambda probe (that normally sets ‘fuel fail
44’)
Another posssible cause is an inlet manifold air leak which when
sensed by the lambda probe will increase the fueling.
Reading your previous post with the erratic idle check the
resistance of the cranshaft position sensor. It is a 3 pin plug
with 2 signal wires and a screen., the resistance of the coil
should be 1.5 k ohms engine hot, outside of that it should be
replaced.
Hope that’s of some help , bearing in mind those codes above relate
to a uk car!!!–
The original message included these comments:

hello list…a few days ago I posted a question regarding the
possibility of a failing fuel pressure regulator causing a Fuel
Fail 23 code on my VCM…I did not receive any responses so please
let me ask the question another way…can anyone that has had a
FF23 code tell me what they did to correct it?..thanks…

–
dave needham
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

3

In reply to a message from dave needham sent Wed 16 Jun 2004:

thanks Dave…I did install a K&N air filter by removing
completely the top portion of the air breather housing and fresh
air tube and putting some silicon sealant around the edges of the
new filter…it is held in place very nicely by the remaining
bottom portion of the breather housing…could the additional air
that the K&N filter is letting into the intake manifold be causing
the system to compensate and run rich thinking there is an air
leak?..–
Cliff - '93 XJ-40 Sovereign (4.0L)
Lancaster/South Carolina, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

4

Cliff wrote:

thanks Dave…I did install a K&N air filter by removing
completely the top portion of the air breather housing and fresh
air tube and putting some silicon sealant around the edges of the
new filter…it is held in place very nicely by the remaining
bottom portion of the breather housing…could the additional air
that the K&N filter is letting into the intake manifold be causing
the system to compensate and run rich thinking there is an air
leak?..

No, that couldn’t be it, because the K&N filter does not admit any more air.

Dave Lokensgard
'96 XJR (DAVZCAT)
'90 Sovereign (MELZKAT)
'90 Vanden Plas Majestic (PATZCAT)
'55 XK140 OTS
Poway, California

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

5

In reply to a message from Lokensgard sent Thu 17 Jun 2004:

You might have poisoned the Lambda probe…They DO NOT like
silicon at all!!–
The original message included these comments:

completely the top portion of the air breather housing and fresh
air tube and putting some silicon sealant around the edges of the
new filter…it is held in place very nicely by the remaining

–
dave needham
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

6

In reply to a message from Cliff Archie sent Wed 16 Jun 2004:

My book says 23 fuel supply, rich exhuast indicated. I had to
splice in a TEE fitting to check my 88 vdp, than unscrew the fuel
pressure gauge of the hose it came with and thread the 1/8 inch npt
into the TEE than I think it was disconnect vacume line, on
regulator on fuel rail{check for hose leaks} and the pressure
should go from 40ish to 90ish psi.–
The original message included these comments:

possibility of a failing fuel pressure regulator causing a Fuel
Fail 23 code on my VCM…I did not receive any responses so please

–
dan peterson
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

7

In reply to a message from dan peterson sent Sat 19 Jun 2004:

Dan,

Where did you find the fuel pressure spec. of 90psi? I have been
tracing down a lean fuel condition and also measured the fuel
pressure on the rail. I had no where close to 90psi with the vacuum
off of the fuel pressure regulator. If I remember correctly, with
the vacuum to the regulator, pressure is around high 30s and 45
with out vacuum. Wonder if mime is to low!–
The original message included these comments:

splice in a TEE fitting to check my 88 vdp, than unscrew the fuel
pressure gauge of the hose it came with and thread the 1/8 inch npt
into the TEE than I think it was disconnect vacume line, on
regulator on fuel rail{check for hose leaks} and the pressure
should go from 40ish to 90ish psi.

–
Jerry 1990 Majestic
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

8

In reply to a message from Jerry Sure sent Sat 19 Jun 2004:

The correct fuel pressures are as shown in the specifications
section of Chapter 4 of the Haynes manual :-

Ignition on, engine not running - 38 / 44 psi
Engine idling - 30 / 38 psi
Engine idling, vacuum hose detached - 40 / 46 psi
‘Hold’ pressure when ignition switched off - 21 psi–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

9

In reply to a message from Cliff Archie sent Wed 16 Jun 2004:

I would first check the condition of the spark plugs, does
discoloration indicate too rich a fuel mix. Also, get the exhaust
gas tested, that would tell you if you had a too rich a mix, or
not. In many cases, FF23 gets flashed up on the trip computer due
to poor electrical connections. Disconnect and clean connections to
the Lambda, air and coolent temp sensors, the connector to the MAF.
Also, the multiplug to the ECU on the low voltage side. (remember,
disconnect battery first before proceeding with the above).
The figures Bryan quoted for the fuel pressure are correct, but I
would question the hold pressure of 21 PSI, it should be higher
than that.
Another cause of too rich a mix is dirty fuel injectors, the
injector is allowing too much fule in, or the injector may not be
closing correctly. Usually a good dose of fuel infector cleaner
will remedy this.

I spent a a few months trying to track down the cause of a FF23
code. In the end, it turned out to be due to some sort of
electrical interference between the wires from the coolent sensor
and the wires from the TPS. Only found this accidently when with
the engine running, I was jiggling all the harnesses looking for a
dodgy connection when the engine stalled. I found that moving the
wires from the coolent sensor towards the wire from the TPS caused
the engine RPM to change. I cable tied the wires from the coolent
temp to prevent them moving about, and since then, no more FF23.

From the XJS workshop manual, the main causes of FF23 are:
High fuel pressure.
Oxygen sensor heater ground loose or engine ground loose.
ECM ground connection at bulkhead stud loose or corroded.
Engine coolant thermostat stuck open.
Purge valve stuck open.
High resistance in MAFS connector.
Incorrect mass air flow sensor calibration.
ON vehicles (with adaptive idle fueling trim): Intake system air
leak - especially between the MAFS and the throttle valve.
‘‘Lazy’’ or defective oxygen sensor.

Good luck–
The original message included these comments:

hello list…a few days ago I posted a question regarding the
possibility of a failing fuel pressure regulator causing a Fuel
Fail 23 code on my VCM…I did not receive any responses so please
let me ask the question another way…can anyone that has had a
FF23 code tell me what they did to correct it?..thanks…

–
Nigel, 1993 XJS 4.0L Conv
Manchester, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

10

In reply to a message from Nigel sent Sat 19 Jun 2004:

Nigel,

You wrote:-

‘‘The figures Bryan quoted for the fuel pressure are correct, but I
would question the hold pressure of 21 PSI, it should be higher
than that’’.

What do you think it should be? When I had a failed fuel pressure
regulator, the ‘hold’ pressure dissipated to near zero within a few
seconds of switching off the ignition (hence my hot-starting
problem) although it was maintaining the required pressure at idle.
I fitted a brand new FPR and the ‘hold’ pressure was exactly 21 psi
when I switched off the ignition and stayed that way until I got
fed-up with watching it and went in to the house for dinner.

What makes you think it should be higher? Is Haynes incorrect? I
can’t find any reference to fuel pressure testing in the FSM on the
JDHT CD.–
The original message included these comments:

The figures Bryan quoted for the fuel pressure are correct, but I
would question the hold pressure of 21 PSI, it should be higher
than that.

–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

11

Bryan,
when I was testing my Fuel pressure, both with an original FPR and a new
one, the pressure stayed around the mid 30’s. It only dropped towards 21PSI
after a period of about 6 hours.
There is no mention of hold pressure in the workshop manuals, but a couple
of mechanics I spoke to on the subject thought that 21PSI after 5 mins of
engine shut down seemed on the low side.
I cannot find a reason why it should drop to 21PSI after engine shut down

Behalf Of Bryan N

What do you think it should be? When I had a failed fuel pressure
regulator, the ‘hold’ pressure dissipated to near zero within a few
seconds of switching off the ignition (hence my hot-starting
problem) although it was maintaining the required pressure at idle.
I fitted a brand new FPR and the ‘hold’ pressure was exactly 21 psi
when I switched off the ignition and stayed that way until I got
fed-up with watching it and went in to the house for dinner.

What makes you think it should be higher? Is Haynes incorrect? I
can’t find any reference to fuel pressure testing in the FSM on the
JDHT CD.

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

12

In reply to a message from Nigel sent Sat 19 Jun 2004:

Nigel,

Strange that the factory service manual makes no mention of the
fuel pressure test specs. I had a browse around various sites on
the internet for relevant information and could only find one
reference to testing which specified the pressures for FPRs of a
similar rating to the ones on our Jags. It was in a Toyota document
and it too specified that the hold pressure should be greater than
or equal to 21 psi, the same as Haynes.

Another of lifes’ mysteries I guess!:-)–
The original message included these comments:

There is no mention of hold pressure in the workshop manuals, but a couple
of mechanics I spoke to on the subject thought that 21PSI after 5 mins of
engine shut down seemed on the low side.
I cannot find a reason why it should drop to 21PSI after engine shut down

–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !