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
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.
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
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