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Need help with an elusive XK8 coil issue? I have a coil that throws a P0356 code ( and the other typical errors when the RS light comes on). If you let it sit for a few hours the coil starts working again. Or if you're trying to get home with the RS light on, it will suddenly start working for awhile and then throw the code again. It seems to happen most often when I waiting a stop light or when the outside temp is high (like 85 - 90).

I know the troubleshooting about swapping coils, and I have swapped several to that cylinder. It currently has a new one, but continues to act the same. To be sure that I am working on the correct coil, is the following correct?

The XK8 cylinder order as I understand it is that from the drivers seat, bank A (01) is the right side and bank B (02) is the left side. The cylinder location for a P0356/P306 error would be cylinder 4 on bank A. Is that correct?

Is there anything else to look at if it throws the same code after I replace the coil with a new one? Is there a module that controls the coils?

 

Never been right there but if the code keeps pointing to that cylinder . . . You say that you replaced the coil pack with a known good one? The JTIS tree looks to the wiring before the coil pack. Coil pack is at the bottom of about a dozen potential problems. I would disconnect the ECM main wiring harness, spray it with a dielectric product and reconnect.

There is nothing that is specific to a single cylinder except spark plug, injector, wiring and ECM program.

Disconnect the battery first ! ! ! ! ! ! ! ! ! ! ! ! ! !

Beyond that you are going to have to trace the wiring.

 

If I disconnect the battery will I have to go through the "adaptions" (driving instructions) for the ECM?

 

Yes, but just drive it and the ECM will reset itself. No big deal.

 

Well, I cleaned the connections at the ECM and inspected the wires and harness at the problem coil to make sure they weren't loose/broken. I drove the car for about 40 miles under various conditions (freeway, acceleration, load, stop and go, wait) and it worked perfectly - - untill I stopped for a light at home. The RP light came on while waiting for the light change, went off when leaving the light and came back on as I drove in the drive. Same cylinder.

Is the next step measuring the resistence in the wiring harness? Doesn't seem logical that this would happen intermittenly or not be a problem when the car cooled down. In the trouble shooting tree, it does mention coil modules before getting to the EMC. Anyone know anything about this? No location mentioned in JTIS. Other diagnostics that can be run that will give more detailed information?

Thanks

 

I had a wiring problem in a car years ago. It turned out that the wire was broken inside the insulation and you could not see anything. When the wiring heated up some, the insulation expanded and separated the wire. When it cooled down and contracted, it reconnected the wire. Just a thought!

 

The ignition modules are mounted on the firewall just behind the engine but I cannot see how they could be only throwing a code on one cylinder unless it is a connector/wiring issue. Cleaning and spraying all connectors perhaps is not a bad idea.

I went back and reread your original post. P0306 and P0356 codes refer to cylinder B2. That is the second from the front on the left side (from the driver's seat) not the 4th on the A side. Since a heat related coil failure is a known issue identified on the diagnostic tree, I would make sure to get a good coil in that location.

 

I'm really confused on mapping cylinders on the XK8. The DTC code shows P0356 as being cylinder 4. How does that become the second cylinder from the front on the B bank? Does the count begin with the first cylinder on the A bank and alternate between banks?

Would really explain why I've been chasing the wrong problem! Thanks, really appreciate the forum.

 

JTIS says that P0356 is cylinder B2. Where are you looking up the code? P0306 also points to B2.

Cylinders are numbered A bank (right from driver seat) 1 through 4 (front to back). Same with the B bank (left).

 

JTIS 303-07 : Diagnostic Trouble Code (DTC) Index

'P0356 Ignition coil primary/secondary circuit malfunction, cyl 4

Same at 303-14

 

I see now in the DTC summaries where it sayes Ignition Coil B2. So I don't know why the discrepancy. When I select XK8 1999 and do a global search it takes me to the above pages. The reader at the bottom shows it is searching with the correct parameters.

I'll try the above suggestion - not that hard to do.

Thanks

 

Indeed, it does say that but if you will go to the 'DTC' logo at the top of the page you will find the P0356 says 'B2' that I referred to.

Guess we have a little JTIS confusion.

If you start at Right Front as 1, Left front as 2, Right second as 3, Left second as 4 you are back to B2. I remember reading some time ago about a change in how Jaguar designated cylinders but had never run into it before.

Try B2.

 

I did switch out the B2 coil with a new one and took for a test drive. No RS code! But the temp outside today is only 71, so I'll drive it for awhile to make sure the problem is resolved.

Again, thanks for all the help.

 

Curious to know how you came up with a #4 cylinder problem when PO 356 is Coil Pack F Pri/Sec Circuit B2 and PO306 is a B2 misfire? Now I know. Bank B is on the left and B2 would be #4.

 

Replaced the defective Coil Pack at B2 with new unit. Car runs great but paid $54 bucks and thought it was a good deal. Now I'm finding that XW93-12029-AB coil packs are used on other cars like Hondas and the cost "new" delivered from Japan and China runs about $17 each with free shipping!

 

Hello Mr Test point and hello to all members. I see your talking about the coil harness and possible deterioration in this area. I just bought a 1997 XK-8 Coupe from Fla and while changing the plugs identified very badly deteriorated plugs at the harness into each coil. Some were RTVed. This is not a good situation I'm sure. But how is something like this repaired??? Do I find a donor car and cut the harness going into the ECM??? Please suggest what I can do. Thank-you for any advice in advance. Be well!

 

Those of us with the old two wire plug are out of luck. If you can find good connecters in a yard it would be bordering on a miracle. They get brittle and break easily, so we all use a dab of RTV to help hold them. There are no new replacements, as far as I know. The only new alternative is the entire engine harness, at a cost that would amaze you.
On the plus side, I have not had a problem with the RTV assisted connection.