Hello, my ND V12 6.0L has caused me to be hanging on my last dangling frazzled nerve. Just started a month ago,no codes. A bank is fowling all six brand new plugs withing 1 hour of run time, looks wet blackish. No black smoke out of exhaust both O2s read normal with lots of activity. A bank exhaust temp is 200 degrees cooler than B bank. Pulling each injector connector on the A bank results in little if any RPM change as compared to B bank. Did a compression test on all cylinders 205--225 psi , swapped coils, ignition control modules, map sensors. Scoped the crank. cam and rpm sensors, clean waves and correct amplitudes, and all in correct timing to each other and TDC. All injectors were replaced a year ago and i have no leak down after shutting down motor. I've checked all wiring from ECU to important sensors. Has my ECU given up the ghost. Any thoughts ,I am grasping. Anybody have any contacts for this ECU repair or know of a used one. Steve

 

Cracked exhaust manifold and good donut gasket on that bank ?

Short term fuel trim on that bank compared to the other , target 0.0 % in all throttle ranges

A leak thinking is positive pressure will suck in fresh O2 between pules down the exhaust line without combustion biasing the O2 sensors to command a richer mixture

Your O2 sensors will function just fine as designed , the O2 content specific reading is another mater

Calibrate both coolant thermostats ? but I think you have 1 common temp sensor for the ECU but is I recall on B bank

From the fuel injector relay to both banks should be a wire splice that can be compromised

ECU connectors show signs of corrosion or missing pinching tabs on the sockets ?. common as the same setup as the inline 6 but different Denso ECU

 

Unfortunately your situation sounds a lot like mine was. Did you read through my thread? Its a long read, play by play. But everything I checked and replaced did not solve the problem. Ultimately.... I replaced the ECU with a used one and all has been perfectly fine since.

Everyones XJ12s are Running Great!

My car also seemed like A-bank was losing power. But I couldn't find out why, and it was driving me crazy too! There were no codes other than a MAP mis-match. The car would run and drive just fine from cold, anywhere from 2 to 20 minutes, then the symptoms would reappear. It turned out that the fault would show up the same every time, after the ECU warmed up a bit. Failure was immediate when starting the engine when warm.

The only potential source I could find of my ECU failure might have been a fuel injector wire at 4A and 5A possibly shorting on the fuel rail. I discovered it right away after failure mode started, but apparently the damage was done?

I had the first-gen ECU LNA1410LC. I was fortunate to get a later version from a 96 parts car, LNA1410NB. I have not searched for a rebuilder for the old one yet.

 

Hello, thank you for all the input, I have no cracks or leaks in the exhaust and i don't believe the thermostats are the problem because the problem shows itself when the engine is cold right from startup. I have a decent new bidirectional scan tool but no LTFT or STFT parameters . I have checked all pins on the ECM and connectors with drag test. I cracked open the ECM for a peek , clean dry absolutely no corrosion or damaged components by naked eye. What difference is there between the LNA1410 NB or NA or LC Any Thoughts Steve

 

Wiring from the fuel injector relay at the left and right bank splice ?

See page 69 at the Black / Light Green wire to the left of the relay in the diagram

Free check

jagxj1996.pdf (jagrepair.com)

 

Who knows what updates were made to the ECUs, but it must have been fairly urgent since the new NA version was installed at 731580. That's probably only 500-600 XJ12s built so far when the update was introduced (out of 4165 or so total production). Then the NB version came out on the 96 MY at 754304, so might have been more of a "routine" update.

You have gone deeper with troubleshooting than I did. So if you want to try my old defective ECU just say the word. It will likely tell you immediately if your current ECU is bad, as then you will have the same running problem I had instead! Of course it doesn't solve your problem if you find your original has burned out.

 

There was a California regulator lawsuit as the ECU did not perform and give a O2 sensor code

Production stopping of the V - 12 a year early was effected by this before the V8 came out

I wasn't there in engineering , just what I read somewhere.

Someone mentioned NA suffix as this may be a North American version / fix

 

The OBDII compliance problem wasn't discovered until 1997. The V12 ECU would not provide continuous misfire monitoring. So that might explain why we don't get any codes during our serious misfire troubles! The violation extended into the first-gen V8 XK8 for 1997 too, but I think dealers could reprogram those ECUs to comply. I recall Jaguar paid a fine to the EPA, and the 15-year USA emissions warranty for the X305 was born.

 

@stevenx605 ... Anything to report with your running problem? Did you seek out an ECU repair or get another one (ECU or entire car)?

 

Hello, it's been awhile. I ended up purchasing 2 ECM's and two ignition modules. The results are mixed. The car runs but have moved away from this car to clear my mind and think of a new approach. I was being consumed. Thank you for all your help. Steve

 

With the fault showing before engine warm up and full engine regulation in closed loop mode rules out the O2 sensors as they are not used until closed loop mode

 

What a crazy problem. I felt defeated after I couldn't find the source of my similar problem. My replacement ECU was the last resort. Turned out the ECU was the sole cause of the issue and it is surprising that it has not solved your problems too. Sorry to hear that.

I hope the XKR is treating you well and you can have great fun with it to make up for the "other one"...

 

Someone recently went inside the V - 12 ECU and found a component on the board problem and replaced the component , best I can recall without looking

1 cylinder can make the whole bank look bad

 

I checked every resistor inside my old ECU and all measured normal and consistent across different locations, at ambient temps.

I did not heat the thing up in the oven and then test them all, which was my failure mode. I should try that.

Of course there are lots of different board components. I don't know how to test the capacitors on the board.

None of it would matter if the defect is internal to one of the many IC chips.

With the batch fuel injection, I can see that one bad FI component could ruin the fueling for a whole bank.