SWIMBO called me a few days ago saying the engine light was on, she got the codes checked at O'Reillys and they said cyl 6 misfire.
I was due home yesterday so ordered up a new coil, switched it out this morning and put in a new plug also, no change still a severe misfire and RP.
I'm getting P0306 P1314 P1316 & P0356
I'm thinking the wire from the ECM to the coil, and going to try and check that now.
Any other ideas?

 

You long ago changed the two IMT valve O-rings from the inferior factory yellow-colored ones to the new-and-improved green-colored ones, correct?

 

I'd be thinking the same.

With the way things are with heat & vibration it's perhaps more likely to be nearer the coil than the PCM - but there again we've had water dripping onto a few PCMs so that's another possibility.

 

First thing that popped into my mind Jon, but then I don't think the other codes would have flagged.

I think Norri is on the right pat thinking wiring.

 

What condition is/was the connector to the coil?
A lot of them get cracked and broken from time and heat.

Maybe just a loose connection?
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The connector looks OK wiggling the wires makes no difference, nor does pulling the plug off completely.
Anybody know what kind of bolt holds the ecm plug on? I can see it with a mirror and it looks like a security torx but I can't get one to go in.

 

It's small and I think it was 8 or 9 mm.
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Turns out it's a T27 5 point torx, Pepboys came to the rescue.
Now the pins in the plug don't match up with the diagram from JTIS the pin that I should want is empty.
I'll try again tomorrow.

 

On the 3.0 I believe there's a many-way connector for the PCM then a short distance away another many-way (18x6?) but different connector. I suspect that's the other side of the firewall (but on my car I've never been able to see enough to be sure).

 

Got the pins figured out finally and I've got continuity from all three coil connectors back to the ECU plug, so that's saying ECU to me, any other possibilities?

I also checked the other three wires back to the other two coil plugs and get continuity there so I'm assuming those are all good as they are common.

 

I'm sure you've seen how rare that is. Send it for repair/testing I suppose.

 

Yes, I was expecting a broken wire.
Can't think what else would do it though.

 

Man that sucks. Can we get Brutal or another Tech directed to this thread?

 

Dear Norri,

My experience with automotive controls is unless the computer throws a code faulting itself, the computer is typically fine. Expensive little buggers to swap for troubleshooting, unless you happen to have a known good spare. As you may have already guessed, I do not care to discuss how I know this...

Since you have already changed the coil and spark plug, and the associated wiring checks okay, you may be looking at a compression issue. Compression is one of the factors affecting the voltage required for a spark to jump the plug gap. Reduce the compression, and the voltage required also drops dramatically. I'm not sure exactly how the system monitors the ignition primary and secondary circuits, but in my little world, it seems entirely plausible that a plug that fires too easily (the arc doesn't have to overcome normal compression) could be misinterpreted and mistakenly flagged as an electrical fault.

Of the 4 codes you listed, only P0356 is what I'd call a primary fault. That's a fault of the #6 cylinder primary/secondary circuit. (Wish I knew exactly what triggers the code.) The other three codes are secondary codes. P0306 = misfire detected #6 cylinder, which actually means low power output from that cylinder, and not necessarily a spark-related misfire. More details from my MisfireSoapbox™, partway down on this thread:

https://www.jaguarforums.com/forum/s...firing-146818/

The other two codes are for a misfire strong enough to cause catalyst damage. To troubleshoot any of the three secondary codes, the manual refers you back to the primary code.


I'd suggest running a compression test to be sure. It doesn't cost anything except for your time. Either you'll find a fault and then know how to proceed, or it will pass with flying colors and you can point out what an idiot I am. Either way, you win!

The only gotcha you may encounter is a weak or broken valve spring. It's possible for the valve to be blown shut during a low-speed compression test, but still manage to stick open at normal engine speeds. I'm not sure how to troubleshoot that scenario.

 

Is the #6 coil actually firing????
You can remove it and inserted a spark plug with a ground lead/wire clamped to the plug body to ground it. Lay it on the engine somewhere still connected to the harness. Start the engine. The plug should spark visibly.

If not then I would suspect the ECM.

I have an old spark plug with a small hole drilled/threaded in the hex area. I attached a wire with a small a alligator/crocodile clip for grounding that I use for this purpose.

Here is a pic of one I found on the internet that someone cobbled together.

bob gauff

 

Uffda, good point! Any chance of the new coil or plug being bad from stock? This is a troubleshooter's nightmare and is fortunately very rare, but it can happen. On another car, I once got a defective distributor cap, only allowing a weak spark to one plug. It fired a test plug okay, but still caused rough running when everything was put back together. It took some serious headscratching to figure out the new cap was defective. I took it back and got another but the rough running continued. I was really stumped until I realized the replacement cap probably came from the same defective batch. I purchased a third cap (different brand, from another store) and then everything was fine.

Forgive my ClavenMoment™ there. I'd suggest swapping the plug and coil with adjacent known good parts and see if the problem follows. Fortunately #6 is on the easy side to access.

 

Thanks for the ideas guys, I had thought about checking spark and compression but got kind of side tracked on the ECU idea after changing the coil and plug and checking the wiring out.
So this morning I rigged up a test with the old plug and an old coil I had and it did spark!
Pulled out all the plugs and checked the three cyls 2,4 & 6 for compression and got 195,195 & 200 so all good there, BUT, I couldn't get the new coil out of the cam cover hole and had to smash it up to get it out, so I boxed it up again with the another new coil on 2 and switched one of the used ones into 6 and it seems all good now.
I cleared the codes and have driven about 30 miles with a few shut downs and restarts and no codes so far.

 

Hope that indeed fixes it. Keep us posted....

 

Me too Jon, driven a bit more since them and it still seems good.

 

without reading through every post but to answer you from pm Norri. P0356 is the driver circuit for the coil. It will ONLY (coil verifyed not the issue) the wires or the ECU. unplug ECU and check the wires for that circuit from the ecu to coil for high resistance, open, cross short or short to power ground. If thats ok send to a rebulder for repair of the driver in the ECU............later