Hello!

Another calamity befalls my XJ12 unfortunately. Checked my oil this weekend after driving around for about an hour. Oil smells a little like gas. Oh no. The exhaust also smells rich when fully warmed up so that's neat. A couple of months back I got a code for a MAP sensor, but just cleared it and it never came back. I've also been experiencing a slight occasional vibration at idle.

I already replaced the spark plugs and wires, so other than the ignition blocks themselves, I don't think it would be ignition-related. No fuel in the regulator vacuum line either. My guess is the injectors need to be rebuilt after sitting for essentially 7 years.

Thoughts?

 

If the coolant thermostats fail open and the coolant stays cool the ECU will not go into closed loop mode

If the coolant temp sensor does not see coolant temps over 88 degree C the ECU will not go to closed loop . faled ECT sensor

You can compare the temp sensor against a table on page 225

www.jagrepair.com/images/Training Guides/801S - 2000.pdf

 

G'day Swagger,

Another possibility is a dodgy or disconnected coolant temperature sensor, the one near the thermostat on the LH head. It sends a temp signal to the ECU and if it is faulty or disconnected then as the engine warms up the ECU doesn't get the signal and the engine runs rich. It happened to me years ago and it was a broken wire in the thermostat plug.

Cheers,
Jeff.

 

The coolant sensor for the ECU is the 2 wire one

The single wire sensor is the instrument cluster

 

Pulled Plugs last night. Only one was rich (Cylinder 2A). Roommate brought his boroscope home from work and there was a small puddle of fuel on top of the piston. Leaky injector it is! Sending the set out to jaguarfuelinjectorservice after reading of the success earlier XJS guys seem to have with them.

To be safe though, I've ordered new coil packs, new map sensors, a fuel pressure regulator, and a coolant temp sensor just to cover all the bases. Might order a whole set of o2 sensors too just to be safe.

 

Okay, so I got a message back from the injector cleaner. He said they were all fine. I went back and checked my plugs and apparently the one on cylinder 2A was set to .035 instead of .03 like the other 11. Is that plug gap enough of a difference to lead to an occasional miss and running rich?

 

If it was running ok previously with that gap surely something else has occurred?

 

Well, I replaced the plugs 500 miles ago. I pulled out the originals (yikes!) and they all looked fine. I'm assuming I forgot to gap this one.

 

I usually manage to screw something up while fixing something else - maybe try putting the original plugs back in and see if the problem goes away?

 

Unfortunately, I threw those out about 7 months ago... I purchased an all new set of 12 again and will re-gap and see.

 

With your identified 2a cylinder being out of sorts can you swap the ignition modules and see if the issue changes cylinders ?

 

^Ordered new ones! Just gonna throw those in any way.

Could an ignition module cause a miss on just one cylinder? Wouldnt it take out the whole bank?

 

With the ignition coil modules having 3 coils per pack to run 6 cylinders of the 12 you would expect the twin cylinder to have problems with one failed coil of the three

See page 232

Notice the original spark plug gap on page 233

801S TITLE (jagrepair.com)

This does not mean a odd small gap plug will not fire satisfactory, but the ECU is looking at the 6 cylinders exhaust gasses as a whole and the one cylinder may not have a satisfactory fuel charge ( rich or lean ) for a successful combustion

Once the cylinder does not consume the O2 it will be seen downstream and will trigger over time a richer mixture to consume the O2 into all cylenders or the left or right bank specifically

How the ignition module ........

Does this V12 still have the distributor cap as the earlier ones you can swap the individual contact points instead of a new distributor cap



Slow YiFIi

 

Not sure about the ignition modules, I assumed they were fine... If all else fails, might replace that.

Nope! No distributor cap. Just the later NipponDenso management with 2 Ford Taurus coil packs

 

Swapping ignition modules from one bank to the other and if you can identify a new mis behaving cylinder on the other bank would prove somewhat a degraded ignition module

If you are by a O'Reilys auto parts store they have a coil tester in the back room

ECU connecter Check ? I know yours is a Denso ECU

 

Good to know! I'll go ahead and finish replacing everything I have with what I have on order. If it persists, I'll try swapping ignition modules.

 

I guess I forgot to mention one thing. The car has always had a little bit of a high idle when cold that lasts longer than most other cars (My 2014 S60 for instance drops down after about 30 secs). My XJ12 idles at about 1500 cold and then drops down to around 900ish from what I recall. Once put into drive it idles around 750. Does this sound right to you?

 

Idle in drive with a cold engine seems to be 950rpm going from the video I have of my car sent by the PO! I would think this settles to 750 or so once it's warm??