In reply to a message from Kirbert sent Sat 20 Sep 2014:
Kirby:
I am afraid that not all of this applies to the 6.0L.
The hot start fuel pressure boost is vacuum to the FPR being
cut off via a temp switch on the fuel rail, a solenoid and a
delay valve, IIRC. No timer.
I have not had the car idle on me longer than 2-3 minutes for
this reason - adaptive fuel trim - topic we covered almost
exactly 1 year ago
I’ve got a fuel pressure gauge mounted permanently on the rail
– I see the fuel pressure increase upon hot start, but than
it stabilizes to ca. 32-33 psig. Vacuum is also very solid 20
in. Hg.Idle speed is ca. 750 rpm.
http://www.jag-lovers.org/v.htm?id=1362255765
Playing with the throttle does not make the idle go up.
Only putting the car in gear and then returning to park does.
Steve
PS The secondary air-pump provides air into the exhaust on
cold start, helping the cats light off. It does nothing on
warm engine. Well, there is a periodic check routine for the
O2 sensors, whereby the air-pump pumps air in the exhaust and
the ECU monitors to O2 sensor responses, but I’ve got this
function disabled on my 36CU by Roger Bywater)–
The original message included these comments:
And my final thought is the air pump. Could the low idle be
related to the air pump kicking on?
That’s a thought – but the air pump kicks off once the engine warms
up. It’s vacuum operated on earlier cars; I dunno about the 6.0.
So, one thing that might be happening is something is FUBAR down
there so that when vacuum is applied to disable the air injection, it
results in a vacuum leak which boosts the idle. I’d presume that
means it also fails miserably to disable the air injection, which in
turn would confuse the oxygen sensors, which would then cause the
engine to run rich?
There’s also the startup timer, right? On US-spec cars it’s supposed
–
'95 XJS convertible - V12 6.0L
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