Why not plug in a simple OBD scanner first and check the readings? It will show up the coolant temperature, oxygen sensor operation(whether closed loop or open), its operational voltage and trims and many more useful info.
It will also show up MAF readings, I wouldnt worry much about 0.2g reading, on my OBD scanners it always shows that unless you're actually driving it, something wrong with the OBD which was 'very young' at the time.
On my own x300 the rews were oscillating at idle because the o2 sensors were mixed up(orientation needed), the fuel economy was down to spark plug gaps(crap when on factory gap or too small, fine on 0.8-0.85mm), but I'd always start any diagnostics with OBD scanner first. The idle also massively improved when using the hotter champion plugs RC12YCC that Jaguar recommended for poor idle.

 

Plugs are RC12YC , typo . O2 sensors can be easily connected up crossed as they fit in either receptical .

Upstream sensor Bank 1 / green

Upstream sensor Bank 2 / brown

Downstream sensor Bank 1 / blue

Downstream sensor Bank 2 / red

The wire color on the receptical side as bank 1 always includes cylinder 1 which is the fwd cylinder on the AJ16 engine different then the AJ6 engine

 

I actually got the RC12YCC in a genuine Jag box(pic attached), CC stands for double copper and single C for copper plus(whatever that means ). To be honest that was the best upgrade I ever done to the car. AJ16 idle is notoriously bad, even good low mileage engines don't idle as good as the earlier AJ6. The hotter plugs finally made the idle acceptable to me.
Theoretically I should be running colder plugs because I run my LWB on LPG but it runs so good now that I'm not going to touch anything. Idle is perfect with hotter plugs, including when running on LPG and currently returns an equivalent to over 50mpg.
Re the o2 sensors luckily my UK car only has two o2 sensors, so was easy to get them right!

 

Hi All,

Many thanks to everyone who commented about my poor fuel consumption. My car mechanic changed the MAF on my car today and the car is driving nicely and is more response when you accelerate. There is a notable difference, so I am optimistic my petrol consumption will improve.

Through addressing / chasing this issue my revs are now constant on idle (new coils (Jap ones), Champion spark plugs, paper air filter (no more K&N) and a new MAF).

Cheers,
Nick

 

Hi katar83,

Thank you for your report. I'm curious to know if you purchased your plugs directly from Jaguar or as New Old Stock from another source?

The RC12YCC was the plug specified by Jaguar to improve performance in cars that were suffering rough idle and driveability problems on the original RC9CC plugs. But since Champion no longer offers the RC12YCC, most owners have opted for the RC12YC. There is apparently no discernible difference in performance between the RC12YCC and RC12YC, but I know some owners would be happy to learn your source for the RC12YCC plugs.

Thanks,

Don

 

New Old Stock from UK eBay. They do show up often there. I've always used RC9YC and RC9YCC in the past and there is a noticeable difference in how the car idles on the hotter '12' spark plugs. Jaguar certainly got this right eventually.

 

Hi All and Merry Christmas and Happy New Year,

I thought the issues with my car were resolved, but sadly they are not. I am really feeling a bit stuck at the moment.

The car drives OK, but is not as fast as I imagined and seems sluggish. At idle the revs oscillate and every now and then drop from 800-900 rpm down to 600 and back up again. Fuel consumption is bad.

I have replaced the spark plugs with Champion RC9YCC
I have replaced the coils with made in Japan ones from SNG Barrett
I have replaced the MAF.
I have removed my K&N air filter (Before replacing the MAF) and fitted a Mann paper filter.

My latest test was to change the spark plugs to RC12YC (not sure if appropriate for a UK car) but they did improve things very very slightly, but not much; the oscillating revs still remain.

One thing concerns me, during this process the RC9YCC spark plugs were fitted in February and when I removed them today they were totally black and sooty. I would have expected them to be a bit yellow but not like this.

Do any of you wise people have any suggestions for me? I suspect I may need to take the car to a Jaguar specialist at this rate.

Many thanks,
Nick

 

black and sooty is generally a rich mixture condition and can be confirmed by a cheap ELM327 reader

Solutions :

intake vacuum leak at idle

cracked exhaust manifold

exhaust flange donut gasket leak

Others ?

 

Yes indeed, but I have no idea what would be causing that or how to rectify it. This is far from normal, especially given that the car only goes 2-3 K miles a year.

 

Hi Nick,

One potential cause of rich running that you have not addressed is the Engine Coolant Temperature Sensor (ECTS). If it has become lazy or is stuck at a reading the Engine Control Module (ECM) interprets as Cold, the ECM will continue applying cold-start fuel enrichment even after the engine has warmed up to full operating temperature.

With an inexpensive ELM327 bluetooth/Wi-Fi OBDII adapter like Lady P mentioned, and a free or inexpensive app for your phone (Torque Pro, Dash Command, etc.), you can read the live data stream from the ECTS to see if it is plausible. You can also test it by measuring its resistance when the engine is cold and again when the engine is hot, and comparing the readings to the table on pdf page 78 in the Engine Management Systems Manual, which you can download here:

Jaguar Engine Management Systems AJ16 AJ6 V12

With an ELM327 you can also read the Long-Term and Short-Term Fuel Trims (LTFT, STFT), which will tell you if the engine really is running rich.

Cheers,

Don

 

Look for short term fuel trim of 0.0 for all engine ranges with the exception of a cold , not warmed up coolant temp

 

You have checked/replaced quite few things already, still struggling and still haven't plugged in an OBD scanner which would instantly show you/us what the problem is/might be.
A bit silly.

 

Plenty of suggestions as to the possible cause(s) but all is conjecture until the vehicle is scanned for codes and the trims monitored.

Throwing parts at a Jaguar can rapidly cost a lot of money and is rarely either a quick or efficient method of troubleshooting.

Graham

 

One of the things that is free to do is to check for corrosion on the ECU connectors that the engine regulation is effected by . Go through the engine bay and clean the several ground wire studs including the hard to get to one by the starter . Your O2 sensors wires effecting your fuel trim are shielded from off setting interference by the ground studs on the upper firewall . You can easily cross connect the O2 sensors as the main 4 wire connectors are the same . Map on post # 22 . Look for some corrosion in the fwd and aft sensor's connectors to the aft rear left of the valve cover that can bias the signal

These task would come under the area of foundation needs of the engine like a dirty air filter or good plugs other then it's regulation through sensor or valving changes .

See the ELM327 video around the 2:00 minute point on fuel trim .

 

Hi All,

Thanks for your suggestions. I have attached an ODBII scanner and used the Torque Lite app. This is the first time I have done this so might not have got all the data I need.

Here is what I found.

ECU returns a fault code of P1621, from reading this forum it seems this is not unusual?

Regarding the engine coolant temperature, my friend and I observed that this rose from around 60 degrees C, after we worked out how to use the app! to around 80 degrees C when the car got up to its normal operating temperature. Am I safe to conclude the coolant temp sensor is OK? I will monitor this tomorrow when the car is stone cold to hopefully see it rise from a much lower temperature.

MAF at idle always shows 0.1g/s and when driving circa 30-40 miles per hour (50-60KMs) rises to 0.3, 0.4 highest we saw when accelerating hard was 0.5.

I was not sure how to view the LTFT via the Torque Lite app, is this also referred to as F/T 1x1 which showed 14.1 when idling and engine fully warmed up.

STFT1 showed 14.1 too, again at idle when fully warmed up.

I have attached a screenshot from the app.

I don't know if any of this information might help point me in the right direction.

Thanks,
Nick

 

STFT should be 0.0 , it may bounce around that point + or - 2.0 . LTFT is something you can leave alone . The MAF is low . A rule of thumb on a MAF's air flow rate at 500 rpm is 1 gram per second per liter of engine displacement so you should be around 4.5 . You should read 1.2 volts on the center ( Green / Pink ) wire at idle . You can read this wire as it goes over the fuel rail as a harness . Unplug the EVAP Control Valve and EGR valve , clean their connectors as they are wired together and may be sucking that 1.2 volts down . May have a shorting fuel injector to ground . The engine may be off a bit on it's regulation but you will get to information you are looking for as a 4.5 MAF . P1621 is a ECU long term memory fault and may be related to the LTFT as it is a stored reference that the STFT starts calculating and adjusting from . Good on the ECT . Clean grounds including the case ground of the ECU ?

Any questions , just ask , The Jaguar Whisper

 

Hi Lady P,

Thanks for the pointers, I will investigate those items when the rain here stops!

One question does the timing advance of 14 degrees look right?

Thanks,
Nick

 

Nick,

Another thought occurred to me. A coolant thermostat that is stuck open will prevent the engine from reaching full operating temperature and lead the ECM to apply fuel enrichment. The temperature gauges in Jaguar instrument clusters are notorious for failing to show any but the most significant of temperature variations, so it's quite possible to have a stuck thermostat but a temp gauge that reads normal or just below normal.

If your ECTS appears to be functioning properly and the ELM327 indicates the engine coolant temp is on the low side, it would be worth replacing the thermostat. The thermostat and seal are cheap and the job is relatively easy, even on the supercharged engines.

Cheers,

Don

 

Hi Don,

Thanks for your thoughts, I will replace the thermostat. One question my car gets to 80 degrees C and stays there, does that represent a normal or low temperature??

Thanks,
Nick

 

14 BTDC degree timing looks OK in my opinion , My ELM327 lost it's licence key and I didn't look at that PID before then for a comparison .