Hi Folks,
Back with more fun and games on my 2009 XF Supercharged..............

Over the last month or two, the car has been acting up above 4000rpm (drops to limp mode), plus it would sporadically lose power and throw a Christmas tree full of warning lights, then rapidly go away but otherwise OK until yesterday when it lost all power on the highway. After a restart, it limped home, but is now showing multiple misfires, mostly on the middle cylinders in the banks (3, 4, 5 and 6). Been looking at live data (idle, 1500rpm, 3000rpm and 4000rpm):

Idle

1500rpm

3000rpm

4000rpm

I checked the fuel pressure: 55-60psi coming from the fuel pump, fairly steady regardless of load. 50 on the fuel rail, dropping to the mid 40s under load. Throttle position sensor seemed to be working normally. Voltage at 14.6V, so good there. Fuel pump was replaced about 9 months ago after the old one failed, replaced the filter at the same time. New plugs/coils over the last 20,000 miles.

The question is, before I start looking for a fuel or ignition fault, should I start with something more sinister like a bad ground or failing ECU? If so, which ground should I check and is there a way to run a diagnostic on the ECU?

Thanks as always for any good advice to start troubleshooting this one.

Chris.

 

Can you post the codes? That will guide the repair. Thanks for the battery measurement but the important one is after the car has sat all night and is cold. With 14.6 V that's a running car and even with a bad battery your running on the alternator. Look for at least 12.6 VDC after sitting all night. Current age of battery?

Won't hurt to check grounds but with a steel body it's generally not a problem. Can't help with an ECM replacement but you could open the case and look for swelled capacitors but again I would do more basic stuff before suspecting the ECM.

You have the 4.2L SC engine - right? I suspect a vacuum leak and the elbow on the SC to the PB booster is a known problem BUT let's see what the codes say first.
Glad to see you have eliminated the plugs, coils and fuel pump. Which could be suspects at this late date.
How many miles on the car?
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Thanks for the quick reply!!

Let me try to answer all of your questions:

Here's the codes:



I did clear all the codes earlier this morning, so these are the ones that came back running it on the driveway.

As you can probably see, the battery voltage is at 11.6V without the engine having run for a couple of hours (the fan and a few other systems were active though that may have pulled down the voltage. It's a Duralast Platinum AGM battery, only about a year old. But this is freezing cold Michigan!!

I expected the steel body to be OK. I do have a 2006 XJR and (unfortunately) am well aware of all of the fun caused by galvanic corrosion on that. Not that it's the right thread, but I'm chasing my third bad ground there causing it to believe the passenger door is open and throwing a passenger airbag fault.

Yes, it is the 4.2SC. Same block as my XJR which I did have to fix a vacuum leak on in exactly the place you're describing. If you've ever tried to get the SC out of that one, you'll know how much fun the bolt under that elbow is to get to and why most people cut a slot there before re-assembly. :-( I really hope that's not the problem.

Thanks again for the help, really appreciate it!!

Chris.

 

Sorry, I forgot to answer one of your questions. It has 120,000 miles on it. My XJR has 220,000 and still runs like new. :-)

 

I'm reluctant to say it is or isn't due to the battery, though 11.6V is low and might be at least part of the problem. I'm sorry I don't know just how cold it is there!

If the O2 sensor is bad it'll need fixing. Looks like it's bank 2 sensor 1 (i.e. upstream) and I expect a wideband one.

Not being happy at highish revs can be coils or blocked cat, and probably other things too such as inadequate power.

Those trims... are weird.

Even if coils ... seems unlikely as several don't fail at once. I suppose wiring could be an issue.

If the batteries in your cars are alike enough maybe swap them if the other has better volts?

 

Thanks JagV8. The weather's been brutal here recently. A few weeks ago it got down to -29C. It's back to around freezing now. Definitely warmer where you are, although it probably doesn't feel like it. I was born in Leicester, so I know how the British weather can feel really cold even when the temperature isn't that low.

I did have a spare fully charged battery that I tried. Unfortunately, no change. I wondered about the trims. A couple of years ago, you were kind enough to teach me a bit about that.

It has thrown another random code: P0506-24 - Revolution speed from idle air control system below the expected level. Not sure what that means??

Thanks!

 

11.6V at -29C (ouch!) may be good.

I was surprised my car didn't play up when I found my battery was 11.8V - and it stayed like that for months (I put a spare in the boot, though). It was even happy unlocked (in a secure place), with modules sleeping as they should. I was always very aware that a low battery is not good, however.

P0506-24 I think is a stuck high thing to do with idle control. But I don't know what it's trying to say is (or could be) stuck high.

I think your engine is quite like mine (4.2 SC) and mine has no separate idle control valve. It uses the TB (throttle body) at a small opening.

How's your idle? How many revs? Stable?

Just in case you're tempted to clean your TB (and I'm not saying you should), be delicate as they've a coating and overall it's a hi-tech precision part.

hmm... might be worth examining some coils and the wells they're in, just in case there's oil or water in there. Better let it get hot so it's not ice!

You could swap coils a little (note which) to see if the codes change.

 

Thanks for all the good suggestions. Sorry I didn't have a chance to try anything yesterday, I spent most of the day replacing all the valves in the cylinder head of my JCW Mini. An exhaust valve burned out before Christmas and I'm trying to get it rebuilt in what little time I have spare. As of now, the head is back on and torqued down. About another 6 hours of work and it'll be time to see if I got the reassembly right.

I have had some time today to work on the Jag. I replaced the coil on #5 with a brand new one, cleared all ECU codes and took the car for a 20 mile drive. I stopped and started it a few times for any codes to re-appear. When I got home and read the codes again, I'm just totally confused. All the misfire codes are gone, the O2 sensor one is still there, but these have now appeared:

P0101-00 Mass or volume air flow - circuit performance/range
P010F-00 Mass or volume air flow sensor A/B correlation

My son normally drives they car, so I hadn't driven it for a couple of months. When I was out today, there was a clear surge in rpm while I was driving. It was consistent. About once per second, the revs rose about 100rpm, then fell. It was present for the entire drive once the engine was warm. The car felt heavily underpowered and at anything more than 1/4 throttle, it was really hesitating. Throttle modulation did feel fine though, not like the TB was sticking or anything. My son confirmed it's been doing this for about a month.

The question I have to ask now is are all of these false codes, driven by an electrical fault somewhere near the ECU? A couple of days ago, the misfires were real. I was able to clear the codes and have them come back, I could even watch the incidences rise when watching active data. Now it's gone.

I did replace the MAFs a couple of years ago, so I don't expect an issue there, but maybe?? The later SC 4.2s have two air boxes and two MAFs, the older XJR only has one. It's the other things my son says it's doing, like sporadically throwing a load of warnings and dropping to restricted performance under hard braking. There was also when it cut out on him last week.

I have the horrible feeling I could be chasing an electrical gremlin I'll never find, even if I throw a load of money at it..........

Willing to keep trying though if you've got any suggestions as to where to go next, as I don't like to be beaten!!

Thanks,

Chris.

 

Most codes are 2-trip i.e. need engine warm up from cold. It'll cool soon at -29!

Those new codes ... yeah could be wiring or might you have knocked the MAF or maybe with a bad coil it couldn't flag those?

Another drive from cold may flag ... er, who knows what!

 

Just wanted to close this thread out.

Unfortunately I came to the conclusion that this one was going to be more than I was willing to put into the car. It was sold locally last week, so now I'm down to just one Jag, my favorite X350 XJR.

Thanks for everyone's help with this one. I'm going to switch over the X350 forum as I have (of course) an odd ground fault to find.