Hey I own a Jaguar XJ L 2012, I have the 5.0L Supercharged V8. This has been an ongoing issue since the engine was rebuilt by the mechanics who I and them refuse to do anymore business with as per a previous thread going in depth about that situation.

I've fixed 90% of the problems with my XJ from air suspension fault, dynamic stability, recalibrating sensor, terrible sound system(blown speaker and amp), changing bad tire pressures and cosmetics on the inside. The Engine misfire has been something I've been chasing to fix for weeks now.

Here's a synopsis of the situation ~

1. Compression Test:
   • Not directly performed due to engine space constraints, but considering the engine runs rich and has power, compression seems solid.
     
2. Ignition System:
   • Replaced all spark plugs and ignition coils on Bank 2 (the problem side).
     
   • Swapped coils between banks – no change, ruling out coil-related issues.
     
3. Fuel Injectors:
   • Ran injector pulse width tests using SDD:
     • Bank 1 (1, 3, 5, 7): ~1.21 to 1.24 ms.
       
     • Bank 2 (2, 4, 6, 8): ~1.14 to 1.18 ms.
       
     • Passenger side (Bank 1) shows slightly higher pulse width, suggesting potential imbalance but not sure as the pcm is adjusting per trim.
       
   • Ran multiple fuel system cleaners (BG 44K, Liqui Moly, Marvel Mystery Oil, Techron Complete, 505 on different tanks) over ~400 miles, improving smoothness but not eliminating misfires.
     
4. Fuel Pressure:
   • Tested with SDD:
     • ~970 PSI at idle.
       
     • No drastic pressure drops under load.
       
5. MAF Sensors:
   • Tested both MAF sensors by unplugging – no change in performance.
     
6. Vacuum Leaks:
   • Performed smoke test – no visible leaks. (Unless I missed/overlook somewhere)
     
   • Sprayed carb cleaner around vacuum lines and intake – no RPM changes.
     
7. PCV and Purge Valve:
   • PCV passed a Swift test with a score of 97.
     
8. Exhaust Inspection:
   • Noticed a slight hissing sound from the driver-side exhaust.
     
   • Suspected backpressure imbalance or partially clogged catalytic converter but again not too sure.
     
9. Adaptation Reset:
   • Performed Powertrain Adaptation Reset via SDD to clear old fuel trims post-rebuild in case maybe it needed after the rebuild.
     
   • Drove for 50+ miles – no noticeable improvement.
     
10. Fuel Trim Data:
    

• Bank 1 LTFT: +8%
  
• Bank 2 LTFT: -5% to -9%
  
  Around maybe 40% load
  

Current Symptoms:

• Misfire on cylinders 2, 4, and 6, rarely 8.
  
• Misfire lessens after warm-up but never fully goes away. (Check engine has stopped blinking since when I first got the car on start ups)
  
• Fuel trims remain imbalanced (+10 Bank 1, -7 to -10 Bank 2).
  
• Occasional hissing sound from driver-side exhaust.
  
• No CEL blinking after adaptation reset, but misfires persist.

• Mechanics also claimed after rebuilding per head gasket job that there was a lot of carbon in the engine that needs to be driven out as they didn't think to clean it while the engine was apart.

• Codes:
  -Random misfire
  -Cylinder 2
  -Cylinder 4
  -Cylinder 6
  -Cylinder 8
  
  I've also used restore and protect 5w-20 oil about 200 miles ago to help the situation.
  

What I Suspect:

• Possible injector imbalance or intermittent failure.
  
• Potential exhaust restriction on Bank 2.
  
• Could there still be unmetered air or carbon buildup affecting flow?
  

Seeking:

• Advice on further tests to confirm injector health without removal.
  
• Insight into exhaust system diagnosis (backpressure test, cat inspection if it could be that).
  
• Any known quirks with the 5.0 SC related to fuel trim imbalance or misfire diagnostics.
• I've been running 93 USA Octane for over 1300 miles now (since I've had it)
  
  Any help is greatly appreciated! I’ve been chasing this misfire for a while and want to avoid unnecessary parts-swapping. Let me know if there are other tests I should run or data I should gather. I've already became failure with the injector replacement process but need to confirm what the issue actually might be. I haven't given up but I'm at a point where I'm going to test the exhaust or rip the injectors out. If I take the supercharger off it will be time to replace the rear coolant cross over pipe, coupler and check the intake valves (which is far from now).
  

 

Have you done any troubleshooting regarding the O2 sensors? These are known for early failure, in fact Jaguar issued a TSB and extended the warranty on them due to these issues. Unfortunately you are out of this extended warranty at this point.

 

Would you expect to get misfires from a bad O2 sensor?
I'd think it would call-out a lean or rich reading, a slow O2 sensor, something more directly identified to one of the sensors, wouldn't it?

 

02 sensor is actually something I haven't thought of, is there a way to test this in SDD? Or do I have to gamble and purchase new parts and swap out?

 

Swap from left to right and compare STFT if the corrections move as well.

 

In regards to swapping the 02 sensor, is thks something I'll need to get the car on a lift for to do from under. I'm guessing it's hard to get to consider the bay space. My XK8 compared to the xj I can't even see the sensors from the bay

 

With four O2 sensors, haven't you been able to look at readings from each side's upstream (or mid-cat in this case) and downstream to see what they look like yet?
Looking at the upstream & downstream would help you see whether to swap the upstream sensors or the downstream.
But then again I'd think the fuel trim imbalance may more likely be a result of what's going into the cylinders instead of a cause.

 

That's why Ive been chasing the issue for so long, one side lean one side rich.

I'll have another data collection session to monitor the downstream and upstream sensors on both sides. But if it's not the 02 sensors, then it would have to be injectors because ignition and fuel pump are out the question.

 

I wouldn't usually expect misfires from a bad O2 sensor, but if it was the cause I'd expect it to throw a CEL. But I would expect a GOOD sensor to throw Bank 2 lean or rich condition codes if a fueling issue upstream was cause for the misfires, which the fuel trims may suggest.

 

Okay, that's what I was thinking.
It made me think because my other AJ133 has an upstream bank 2 O2 sensor I need to replace that's reacting slow and it's easy to observe with my OBD reader.
I think I mis-understood the sequence of the conversation and thought the O2 sensor might have been related to the misfire.
I'd expect what you're saying that the sensor would identify a rich mixture when too much gas is getting in the fuel mixture.

...but then I suppose if the O2 sensor read a constant, hard lean reading (maybe from a short or open) it would try to correct by adding gas to the fuel...
I don't think I've ever heard of that though, so maybe not really possible.
And as you pointed out, a reading like that would throw a code of it's own anyway.

 

Note this: An failing O2 sensor can give data output what is not outside of the range to lit MIL light, but as a result the mixture in combustion chamber is wrong because the mixture is corrected with faulty values sent by O2 sensor.
(Compare: You read outside temp from fauly thermometer showing nice summer day temp when its actually snowing outside)
Shall not trust any sensor(s) output when seeking an issue: The issue can be the sensor itself.
How about fuel pressure? Was it so that each rails/bank have own high pressure pump or is the rails connected?

 

I believe the rails are not separate, there's a aluminum pipe or metal pipe that extends in front of the supercharger to the other rail if I remember correctly.

Also for another piece of information, after the rebuild the mechanics said there was a lot of carbon build up in the engine, again.. wish they took pictures or opted to clean while the engine was apart. But I'll never know how much carbon is there until the day I remove the supercharger to service the coupler and aluminum crossover pipe.

If the carbon is burning out, I would also assume it could cause a rich condition? And it's drawing more air causing the other side to run lean to balance while reducing the richness in the problem side?

That's the only way I'd see the carbon thing having it's on scenario if its not the cause of injectors or false readings from the 02 sensors

I didn't get around to data collection today as I was busy with work

 

What is your reasoning to conclude that compression is within spec if you haven't measured it? An engine with bad compression in one or more cylinders can still feel like it makes good power, especially considering it is supercharged.

With all the diagnostic you have been doing, I think it is time to perform a compression test. Seeing your work on the rear speaker shelf, you are definitely capable of removing the firewall scuttle panel to access the spark plugs.

Misfire could be lessening after warm up because materials expand with temperature increase and it decreases a compression leak-down in the affected cylinder(s). Is the misfire mainly prevalent at idle or low load conditions?

Not saying that it is 100% the issue, but it's worth ruling out before you start loading the parts cannon.

 

Misfires according to sdd after being warmed up get a bit worse under load, counts go up. At idle it can barely register them. But now adays under no conditions will the check engine light start blinking. Only sdd can read in real time the engine is misfiring.

If I gauge them on how it feels from the cabin I feel a bit insane trying to say whether it's smoother under load since the revolution is of course higher. At idle you can just feel it because the engine idles around 600 rpm.


You're right, only thing holding me back from actually doing it was finding out the procedure and having a gauge, and what to pull to disable the fuel pump so I can crank without the engine starting and spitting fuel.

I have a friend with a Hyundai shop that I have access to go to when he's off work. As long as I research and plan what I'm doing before hand I have 2 hours with shop tools and a lift.

 

You don't need access to serious tools or a lift for a compression test, and 2 hours may not be enough. The wipers have to come off to remove the windshield cowl, which you need to remove to remove the scuttle trim, and then you'll need to remove all the ignition coils and pull the wiring harness out of the way. I use a pitman arm puller to remove the wiper arms. Auto parts stores will loan you both this and a compression tester for free.

 

Boy are you right about those wiper arms. A stout puller is the only way I have been able to budge them. When they release it's with quite a "pop" too.

Here are the two main styles of pullers. Now the single screw type shown was not deep enough to place the pushing screw on the wiper arm on my 2014 XJR. It's made too shallow.






One odd thing about Jaguar wiper arms is they are smooth on the inside bore when new. As you tighten them up it forces the splines into the wiper arm. This makes them almost a single piece of metal and there is no key so you can install the arm in any position. I now use a piece of chalk to mark where the arms are BEFORE I remove them. Just saves some time as otherwise I have taken them off and on a couple of times to get the arms where I want them.

I have done a compression test on my 5.0L SC and it was not fun.
.
.
.

 

Hey guys, so I completed the compression test, I didn't remove the cowl I just went went around it as I previously did when changing ignition coils on bank 2.

As for bank one, I used/tested cylinders 1 & 3 as reference as the whole bank 1 is fine.
It's bank 2 that's the issue. While we compression tested we also borescoped. And surprisingly enough... The intake valves are void of any carbon.

Cylinder 1 - 148 psi
Cylinder 3 - 145 psi


And then for bank 2 which is the misfire side

Cylinder 2 - 149 psi
Cylinder 4 - 142 psi
Cylinder 6 - 145 psi
Cylinder 8 - 142 psi







These are pictures from us doing the tests, we did it in his shop so we had more light.

Here's the screenshots from the video I took of us viewing the valves










These are 2, and 4, walls have no scoring by what I can tell--------- and valves are clean, 6 and 8 looked the same.

Also to add, I replaced the PCV valve yesterday just in case it was that but the membrane was perfectly fine but still replaced it.






So by what I'm guessing, it's most likely a faulty/leaky injector and the car is trying to compensate by decreasing fuel across the engine equaling a higher trim on bank 1 (leaner) to balance.

I'd love to know your experience on this if I'm right to think that at this point. I'm planning to purchase a full set of 8 injectors and replace all on bank 2

 

I'll report back after the injector change, currently ordering a set of 8 Bosch injectors and the tools needed. I already have several cans of seafoam and PB blaster.

 

Hi,

Be aware that there are lot of counterfeight products in a market when ordering injectors. There are thread for how to detect counterfeight Bosh injector.
Been seen that the box where the product is delivered are original, but somebody in the delivery chain have been swapped the products inside. Even sold by offical service desk.
Nowdays i always ask the fellow on counter open the box and show me the product(s) and i took an pic of it on the moment of sale.
On brakedisks they estimate that up to 60% of sold "branded" (Ferodo, TWR, ATE, etc..) rotors are actually by pirate made. Not sure if this is true, but rotors are easy to make and many drivers donīt care if they shake a bit when braking, what are first indication of "out of qualify" rotors.

 

Yeah I actually noticed this on eBay from sellers where they look like the Bosch ones.

And then there's some that included the box, can you please link the thread where they show how to determine which ones are the fake one and which one are the real ones.