I have been chasing three issues with my XJR6 over the past couple of months:

1) Misfire and rough idle, most noticeable when engine is beyond 50 Deg C.

2) Temperature gauge in instrument cluster does not work (but heater functions)

3) Engine stalling/ dying once hot (above 70 Deg C) - when coming off the throttle, revs fall below 600rpm and engine dies. I can start it up again, but the revs immediately drop and same routine happens. This started to happen more often after I changed the O2 sensors to trying to fix problem number 1.

The car doesn't throw up any OBD codes, and this is what I have done so far, which hasn't fixed the misfire:

1) Installed new temperature sensor and sender on the thermostat housing;
2) Removed and cleaned the throttle body (it wasn't really dirty at all)
3) Removed the mag, intake hoses and ducting to give it a good clean
4) Replaced thermostat with new original part
5) Replaced old CKPS to a new original part
6) Replaced all old 6 coils to new Lucas original parts
7) Changed old sparkplugs to Champion RC12YCs
8) Installed 2 new 02 sensors

Anyways, at this stage im thinking either there is an issue with the ECU, I've blown a head-gasket, or that my Catalytic converters are bust.

There is a Jaguar dealer about 12km from where I live here, and i'm thinking i might just give in and take the old girl there for a checkup, but would appreciate any further ideas or suggestions!!

 

I've also added a couple of pictures of live readings from the OBD scanner, with the engine warmed up and idling. Any hints would be much appreciated!!

 

First of all, if your headgasket is gone you should see white smoke.. and oil in reservior, it does look like ur running lean and im guessing the car stalls when its warmed up? I would warm the car up first, when it stalls unplug the engine coolant temp sensor, run it again see if it stays running and smoothly

 

Thanks for the heads-up FrozenApple!

I removed the sensor when the car was warm this morning, and after that the car still misfires between idle and 2000rpm, but didn't die anymore when coming off the throttle to idle.

I then took the car for a short drive, and again other than the rough idling it was driving well.

When I returned home, I put the car into reverse...and then it died. After this, the same symptoms returned, and the car kept stalling consistently when coming off throttle to idle. Furthermore, after each start up, if I gave it some gas, the exhaust would blow out black smoke for 1-2 seconds (I guess this indicates the engine running rich?).

 

ok ummm lets figure this out, I had similar problem before where car would idle and drive fine but as soon as it warms up it would stall on me. Turns out it was the crankshaft sensor, but you already ruled that one out. When u unplug the engine coolant temp sensor the temp sensor sets a default value where is below -18 ? that would also trick the car into thinking its cold and needs to warm up by dumping more fuel and higher idle speed, but seems like you are still miss firing and idle is rough.

1. Did you clean the throttle body?
2. Did you check for vac leak? there is alot of hose going to the throttle body on our xjr6
3. I know you just got new ignition coil but lets test them anyways, one of the method people suggest is wait till its night time where its very dark, remove your cover for the coils then start the car if you see sparks on the coils then it means they are defective. Make sure the car is warm
4. When you removed your o2 sensor, doesnt it need o2 sensor orientation?
5. Check Automatic transmission fluid, if its low it will stall the car too

 

Clean up all your earth's under bonnet.i had same rough run n ingredients changed everything but after cleaning earth's one of my poor running g 02 sensors started working correctly...after lots of head scratching and parts replaced

 

Show me the screen on your OBD2 reader that indicates the temp of your coolant or engine.

 

Vee - I see the pictures sent show ECT is 87C - is that what you mean?

 

Oddly Lady P at idle runs the same short term fuel trim of +24.2 ( as in the 2nd and 4th pic ) and goes toward 0 at throttle up . No codes . I'm going to stay out of this one and learn from the more experienced .

Thanks , Parker

 

I missed that one! Yes, engine temp is where it should be.

Because your short term fuel trim is maxing out lean, I'd say you have a vacuum leak. Lady P, I think you have a textbook vacuum leak somewhere, since the SFTF goes to zero when the throttle opens up.

Ali, what happens to your STFT when you hit the throttle.

When cold, block off the air intake just past the MAF sensor by wrapping the end of the inlet with plastic wrap.

Then disconnect the camcover vent hose going into your intake elbow and blow smoke through it. You'll need a cigar or something. Hopefully you'll see smoke coming out of somewhere... maybe the IACV, maybe the intake manifold? Keep blowing smoke in and hopefully you'll see some smoke leech out.

If not, you may have to take it in to a shop with a thorough smoke machine.