Hi team!

I'm a recent happy owner of a 5.0 XKR in New Zealand. My father has owned several Jaguars including an XFR and 2x F-Types so you could say it runs in the family. I got this XKR for a very good price so therefore have a few jobs to do to it. So far I've got it booked in with Jag for an oil change, Brake and Coolant Flush. I've done the power steering already and will do the Diff when it comes in. Will probably get jag or my local BMW specialist to do the transmission fluid. I have 65,000km on this car.

However the point of this post is to see if I can get some pointers on a rough idle that I'm experiencing. It stumbles or feels like it is missing on both warmup and while idling in all gears including park, neutral, reverse and drive. I can see the RPM needle move around and the idle seems to bounce within a range of around 60rpm or so. When driving the far feels strong and no breakup is experienced.

I don't have any codes indicating an issue at all, but have hooked up my scanner to take a look at a few values. The one that stands out to me is the difference in the 2x secondary O2 sensors, but not sure if that is a red herring and indicating something more upstream. I would assume a vacuum leak would run a 'Bank X lean code' however I have replaced the vacuum line to the supercharger relief valve as that had perished. I also sprayed around some starter fluid on different vacuum/breather lines to see if that would affect idle, and no result.

I've attached a few pictures of some values of me driving/idling with the scanner hooked up. The Pre Cat O2 sensors seem to be inline with each other generally, but the post cat are on the **** with the bank 1 sensor seeming to be very slow in comparison to the second. Does the 5.0 engine use the post cats to modify fuel trims and would them being so off between banks cause some idle issues?

Finally, my long term fuel trims are quite different. Bank 1 is -3.1% and Bank 2 is 7.0%. This would suggest that I would potentially have a too lean issue on Bank 2 if I understand the trims correctly. Both CATs are at 900 degrees.

I'm in the process of removing the MAF sensors to clean them. This leaves either the sparkplugs/coil packs as a potential issue or potentially a failing O2 Sensor? Could this otherwise be an engine/trans mount that has failed and the 'rough' idle is just from the increased NVH?

I've also put some injector cleaner in the tank in case it's a failing injector. Fuel Rail is at around 15000KPA at startup and sits around 7000kpa at idle.

This is a lot trickier without any DTC codes so any other pointers/thoughts would be appreciated so I don't just throw parts at the issue.


Fuel Trims

Prim O2 while Cruising Idling

Sorry for the crap picture. Prim O2 while causing/idling

Prim O2 while idling (note scale)

Secondary O2 Cruising

Secondary O2 Idling

Secondary O2 Idling 2

Secondary O2 Idling/cruising

 

Had a look at the MAFs today and gave them a good clean. Nothing promising happened and idle is the same. I checked the scanner and ran through all the VVT/CAT tests and they all were within range. I moved onto the misfire counts per cylinder and have gotten a little further. I think the O2 readouts are a bit of a red herring and I am probably chasing a plug/ coil issue.

Here's my collated data per cylinder with the misfire counts. this is idling for a few minutes and taking it around the block for about a 5 min drive.



Cylinder 2 is the worst, followed by Cylinder 3 and then 8. From what I understand a bad fuel pump usually starves Cylinder 5/7 so I would rule that out. I am pretty sure it's not a stuck injector as I'm not blasting out fuel. So I would lean away from a fuelling issue and more to a spark issue. I might try be brave and see if I can swap around a few coils and see if the misfiring follows the packs. Otherwise also teeing up some plugs so will check out the condition of those as well.

 

Changing coils around is not a hard job, just takes time on the dismantle. How you considered a smoke check?

 

That might have to be on the list if the ignition issue goes nowhere. One bank being lean seems to indicate a bit of a leak somewhere.

 

May as well pull the plugs - check the color on the tips - mine were just right.

 

Good thing dude has a 5 liter. Even looking at the coils on a 4.2 takes at least an hour. Remove the Entire Intake System, one part at a time.

 

I have pulled apart the intake going to the throttle body. Someone had done a bodge job as the air intake hose that joins the two intakes right at the body had broken at the TB, so they had added a silicone joiner to make up for the breakage. This is not leaking but have a new part on order.

I'm suspecting that it is one of the breathers causing the richer fuel trim. I've swapped around a coil on the drivers (bank 1) side, but getting to the bank 2 coils are going to be a mission from the looks of it. Nothing gross in the bank 1 spark plug holes.

 

Swapped around some coils on both banks and didn't seem to make a difference. The plug holes looked super clean. Once I've had the Jag serviced i'll get around to replacing the plugs as part of maintenance anyway. I'm also wondering if what i'm experiencing is more related to one/all of the engine mounts on their way out. Very tricky business tracking down when there's no codes etc.

 

Chances are high it’s one of the fuel pumps, happened to me, car would idle a bit funny, no codes would pull really strong but only when I was hammering it and only sometimes it would throw a low fuel pressure code, so I’d been down the route of chasing misfires, swapping coil packs, and all sorts.

And it was indeed one of the high pressure fuel pumps,

here’s an easy test you can do,

get under it and locate your two high pressure fuel pumps. Bottom left side of the engine looking head on, they’ll have a foam cover over each one. The car will run on just one pump but not on a bad one, so disconnect one of the electrical connectors on the front pump and start it up.,,

then reconnect and disconnect the other rear pump and start it up, you’ll find which pump is bad because it’ll be lumpy as heck.

replace both.

 

Thanks for the heads up. Sounds like a good easy thing to have a check of. Seems a bit of a pig to replace but will scope out how DIYable it is and if it matches the criteria first of course.

 

Unplugged one at a time, and started it up. Both times, started the same and had no difference. So I guess the pumps are fine in my case then? Unless I should have been letting them idle for some time.