I read some other posts related to these specific codes but didn’t find a specific resolution.

Some people on the forum suggested not to chase the coils because it probably isn’t the problem. I brought the car to a Jaguar mechanic and he said to replace the coils. I asked him if the problem might be a vacuum leak and he said he didn’t think so because he didn’t get any information about lean or rich fuel mixtures. So I replaced the coils and the codes came back in a couple of weeks.

About half the time I start the car it idles roughly. After I drive it for a minute that seems to go away. When I accelerate normally the car runs smoothly. When I accelerate hard the cars jerks significantly. Someone else told me that the jerky acceleration might indicate a bad catalytic converter.

So I have three questions.

#1 Can a muffler shop do a test to confirm if the catalytic converter is good or bad?

#2 Does a 2005 Jaguar XJ8 (4.2 liter, non-supercharged) have one or two catalytic converters?

#3 Does anyone have any opinions on what the problem is likely to be if not the catalytic converter?

Biff

 

Hi Biff,

Sorry in advance for what will be a rambling post, but I'm just going to think out loud.

Coils are known to fail, but three coils rarely fail simultaneously, so I'm disappointed in the Jag mechanic who sold you all new coils. That suggests you need to find a mechanic with a better understanding of your car.

All the affected cylinders are in the same bank, Bank 1, or the right hand bank as viewed from the driver's seat, so my first suspect would be the power supply or control circuits for the coils in cylinders 1, 3 and 5. The cylinder numbering for your engine is on the right in the diagram below:




The Diagnostic Trouble Code Summaries manual is very helpful in diagnosing codes because it identifies the system or circuit that has triggered each code and gives some of the possible causes. You can download the manual here:

X350 DTC Summaries Manual

For example, here are the listings for P0300. P0301, P0303 and P0305 are specific for cylinders 1, 3 and 5, but the possible causes all refer back to the P0300 master code for misfires. P1316 indicates that the number of misfires is so great that the catalytic converter could be damaged - it does not indicate a problem with the converter, only that the catalyst in the converter could be damaged by the misfires. Here are the listings from the DTC Summaries:





Note how many of the possible causes are the same for the P0300 series of codes and the P1316 code. I would personally begin my diagnosis by ignoring cylinder-specific codes for now, since it is less likely that multiple coils or fuel injectors are misbehaving simultaneously or that you have broken valve springs in multiple cylinders. The spark plugs could be a contributing factor if they are original and it would be worth replacing them just to rule them out. Contaminated fuel or a fuel supply problem could be a factor, but we would expect at least some Bank 2 cylinders to also be affected. So my first suspect would be something that can affect multiple cylinders in one bank only, and of those listed, the first one, "ECM to ignition coil primary circuit fault," is the one I would investigate first.

You can download the Electrical Guide for your car at this link, courtesy of our member Gus and his website, jagrepair.com:

2005 X350 Electrical Guide

The ignition coil circuits are shown on pdf page 63 of the manual, Figure 03.4. Examining the circuits, all the coils receive a constant 12V from the ignition coil relay via individual wires that are Red with a White tracer line (color code RW). The ignition coil relay is R7 in the Front Power Distribution Fuse Box in the front right corner of the engine bay. You can check for 12V on the RW wires for the coils with the key turned to Position II (ON) but the engine not started.

If coils 1, 3 and 5 all have good 12V supplies, it might be worth swapping three Bank 2 coils into these positions and confirming that the fault codes do not move to Bank 2 but remain at cylinders 1, 3 and 5. If the codes move to Bank 2, the coils are probably bad. But if the codes remain at cylinders 1, 3 and 5, then our primary suspect becomes the electrical circuits for those cylinders.

The ignition modules, which are built into the tops of the coils, are all grounded via black wires, but the ECM fires the coils by grounding each one individually. For coils 1, 3 and 5, the ground wires connect to the ECM at pins 87, 88 and 89 of the ECM electrical connector. Since all three coils connect to the ECM on adjacent pins, and since water ingress of this connector is a known issue, the first thing I would do is check the water drain below the ECM connector to see if it is plugged with leaves, seeds, etc.

The ECM is mounted behind the glove box on LHD cars, but its connector is on the engine compartment side of the firewall below the passenger cabin micro-air filter housing. Shine a good flashlight/torch under the housing and look for any signs of dampness and leaves and other debris that can clog the drain. If you see any, the next step would be to remove the filter housing and disconnect the ECM connector to check for corrosion on pins 87, 88 and 89. Disconnecting this connector requires a special 5-lobe security or "tamper proof" Torx bit with a hole in the center to fit over a pin in the center of the screw that secures the connector to the ECM. I bought a set of 5-lobe security Torx bits on eBay for about $20.

If all seems well at the ECM connector, the next step I would take would be to check for continuity or shorts in the wiring between the ECM connector and the coil connectors.

Please keep us informed.

Cheers,

Don

 

Thanks Don for your reply. The detail is really helpful. I will update this thread with my progress. It might be a week or more before I get to it.

 

1

 

I was very busy for a while and unable to try the helpful suggestions but my problem has finally been solved. I was rear ended two weeks ago by a woman named Iwona and my car was deemed a total loss by the insurance company. I am now able to report that my XJ8 L is no longer throwing any codes.

Coincidentally, my wife was driving her S-Type 10 days earlier and she rear ended another woman. My wife's S-Type was also deemed a total loss by the insurance company. Did I mention my wife's name is Iwona?

During my wife's crash, her friend Iwona (a different Iwona) was driving on the same road and witnessed the crash. Yes, that is 3 Iwona's. And we all live in the same small neighborhood.

I have learned two things. #1, if you wait long enough, your car problems will be solved for you and #2, don't drive anywhere near a woman named Iwona.

Biff

P.S. - I received a little whiplash (despite a serious and scary snap of my neck) but I think my recovery will be without problem. I haven't noticed any changes in the wife.

 

Biff,

I'm very sorry to hear about your Jaguars but thankful that everyone involved is reasonably OK.

Given the odds of three women named Iwona being involved in these concurrent events makes me think you should be very careful during thunderstorms. Every year a few hundred Americans are struck by lightning, and with your luck those odds seem like a sure thing!

Cheers,

Don

 

Don, there is nothing "rambling" in your assessment or suggestions for course of action. It's very logical.


And thanks Biff for closing it out. There is nothing more frustrating that combing through threads, finally finding one that matches your issue, only to find the original poster never got back. So even though we don't know what was causing your issues, you closed it. Thanks.