I’ve been an XJR owner since 1989 and my current car is a 1996
model. I have got a serious misfire problem which my [non-main
dealer] jag mechanic cannot diagnose - so it would seem to be
nothing obvious like the plug coils. It’s ok on idling and low
revs [although it is a little lumpy] but when the revs go up it
misses like fury, the engine jumps around wildly and the engine
revs then drops to nearly cut out. Any ideas anyone?–
Chris Powell
Warwickshire, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from chris@golfotels.co.uk sent Sun 11 May 2003:
The imperfect nature of DTC trouble-shooting flowchart is well
known, but the fact OBD II does not, and can not, report sensor
malfunctions as long as signals remain within set limits, is often
overlooked. In other words, absence of DTC does not mean proper
operation of sensors at all. For example, if a sensor is supposed
to operate within 4k and 400k ohms, and reads 10k Ohm when it
should report 200k Ohm, OBD II and ECM have to take 10k Ohm on its
face value. Being half-broken is always difficult to diagnose.
Moreover, some sensors are nearly impossible to test for high rpm
or high vehicle speed conditions, and replacement is often the only
effective test.
Apart from all the sensors, leaks in the intake tract and
insufficient fuel pressure, both at high rpm, come to mind. Is
fuel filter on his ‘obvious’ list?–
x300@'95XJ12
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from chris@golfotels.co.uk sent Sun 11 May 2003:
If your VIN # is between 720001-770946, TSB 15-35 indicates that a
wiring harness clip located on the right side of the engine
bulkhead can cut into the harness causing a short circuit. This
clip may not be present on all cars. This clip can cause an engine
misfire/no start condition. Recommendation is to delete the clip
and repair harness if damaged.
My harness was not damaged. I retained the clip but insulated the
wiring in its vicinity with electrical tape to provide additional
protection.–
Dave J 1996 XJ6 (Canada)
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
Sounds like a fuel delivery problem. Misfires are almost always function of load and, I can’t tell from your original message, that load is part of the equation. If you’re parked and step on the gas and it stutters it’s probably a fuel/MAP problem. If you’re moving and step on it, and it misfires, it’s probably coils or plugs. Someone already posted a reasonable response but I don’t see why your mechanic can’t back probe your sensors while jockeying with the pedal while it’s stopped. Could be that the output of one of your sensors it “stuck.” i.e. if the ECU is expecting 1V at idle or zero percent and it gets 1V at 70% that could cause your problems. This applies to just about every engine management sensor under your hood.----- Original Message -----
From: chris@golfotels.co.uk
Date: Sun, 11 May 2003 15:10:23 +0200
To: x300@jag-lovers.org
Subject: [x300] 1996 XJR engine misfire
I’ve been an XJR owner since 1989 and my current car is a 1996
model. I have got a serious misfire problem which my [non-main
dealer] jag mechanic cannot diagnose - so it would seem to be
nothing obvious like the plug coils. It’s ok on idling and low
revs [although it is a little lumpy] but when the revs go up it
misses like fury, the engine jumps around wildly and the engine
revs then drops to nearly cut out. Any ideas anyone?
Chris Powell
Warwickshire, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–
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I would tend to agree its not ignition coils, as its highly unlikely more
than one would go at once and one failing would cause a regular misfire -
different to the condition you describe.
First thoughts are fuel - failing pump, blocked filter or bad regulator - as
the problem appears demand related. Does the miss occur at low rpm if you
put it in drive and apply some throttle ( increasing fuel demand ) without
the high rpm? Also check the aux fuel pump fuse.
Next on the list would be CPS - it may be failing to give a suitable pulse,
such that at high rpm the ECU is unable to resolve the signal and so gets
mixed up as to the real speed of the engine.
A malfunctioning MAF, or associated bad connection, would cause a bad
mixture kind of misfire, whilst an inlet manifold or other air ducting leak
would have a similar effect.
Hope this helps a little - Jez> It’s ok on idling and low
revs [although it is a little lumpy] but when the revs go up it
misses like fury, the engine jumps around wildly and the engine
revs then drops to nearly cut out. Any ideas anyone?
In reply to a message from chris@golfotels.co.uk sent Sun 11 May 2003:
There was a recent problem reported just like this. Check the
archives. The solution was that this XJR has TWO fuel pumps, the
second one was not kicking in as programmed, to provide the
additional fuel needed at high rpm. It is a fairly simple fix as
long as you know about the two pumps.–
Brian Caro
Newport News, VA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–