This has happened on two of my jags, the current 1996 and my previous 1997.
I am wondering if this makes sense:

MY SYMPTOMS:
On cold, wet mornings (I live in Oregon so this happens a lot) it starts happily, but runs unevenly rough for first 6 miles or so.

Once it's warmed up, it's fine (though there may still be a miss in there at cruising speed, but hard to tell for sure)

Gas mileage is down by 10% or so.

Check engine light came on a few weeks AFTER the rough running started happening.

HOW TO DIAGNOSE
1) Check engine codes
See if one or more cylinders show misfire
2) Check coil ohm resistance (should be .75ohm primary resistance, the resistance measured across the pins in the connector.)
3) Can also pull coil wires one at a time and see if symptom can be re-created on warm engine.
4) Check spark plugs for age-related issues, Also check around plug for signs of sparking (grounding to block)

HOW TO FIX:
If coil ohms are wrong, replace coil.
Using third-party brand? If yes, where do I find them?
Replace plugs with Champion plugs.

OTHER INFORMATION:
On my previous Jag my mechanic said the same symptoms were caused by a coil, and said they were expensive, so I opted not to fix it as I was going to sell the car anyway.

Thank you!

REFERENCES ON THIS FORUM:
https://www.jaguarforums.com/forum/x...eration-69757/

 

My 3.2 did similar, but more of a hunting as it went thru 1/2 warm to Normal. New CTS (Coolant Temp Sensor) fixed 60% of that.

Then the CAS (Crank Angle Sensor) died, and when I unplugged that dumb vertical loom plug at the front of the engine, I was shocked at the "muck" inside that plug, and the contacts of the 2 plugs were compromised. I cleaned them, and sealed that plug with RTV when fitting the new CAS, and that made a smaller difference.

Its still there as it passes thru that temp range, and the new owner lives with it, and hardly notices it.

There is NO missing on acceleration etc.

It runs NGK plugs of standard spec (nothing fancy), and runs our 98 RON fuel.

The coils are the originals, and test fine.

 

Grant hit two great suspects. If the engine coolant temperature sensor is reporting to the engine control module (ECM) that the engine is warm or hot when it is actually cold, the ECM will not apply cold start fuel-enrichment, leading to lean running until the engine warms up.

And as Grant also suggests, symptoms like this are often due to more than one component misbehaving. So how long has it been since the car had a good tuneup including air filter, fuel filter, the proper Champion plugs (RC12YC), cleaning the battery power connections and the ground points associated with the engine management system, etc.?

It would definitely be helpful to have the car scanned for any flagged diagnostic trouble codes (DTCs), to also have the short-term and long-term fuel trims checked (STFT & LTFT), and to also observe the Live Data to see how the various sensors are behaving.

Please keep us informed.

Cheers,

Don

 

Grant,
Thanks for the tips, I'll dive into it in a day or two as time permits and report back.

Don,
You wrote:
"And as Grant also suggests, symptoms like this are often due to more than one component misbehaving. So how long has it been since the car had a good tuneup including air filter, fuel filter, the proper Champion plugs (RC12YC), cleaning the battery power connections and the ground points associated with the engine management system, etc.? "

Please note that after I read this I immediately shrunk into myself and scuffed my feet on the ground while avoiding looking anyone in the eye.
:-)

Thank you both!

Charles

 

No shame intended, Charles! We all let these things slip from time to time.

Please keep us informed!

Cheers,

Don

 

Parts are ordered for a tune up. (and I jsut order the Coolant Temp Sensor - I had forgotten about it)

I checked the CPS plug - clean and dry.

I checked the codes - two appeared:

• persistent misfire
• misfire on cylinder #6

I checked the coil's ohm readings - all were 2.2ohms initially, then they bleed down to 1.4ohms after 20 seconds or so. NOTE: I used a cheapie Harbor Freight VOM with fresher battery.

I didn't pull the coils yet to check for charring or shorts. I'll do that when the plugs arrive.

Next up: install plugs, filters, sensor when they arrive.

Thanks again for the help!

Charles

 

Chuck,

You're making progress!

Just a tip to help other forum members give you the most accurate input: when you scan codes, please post the actual code number here rather than just the definition, since often more than one code share similar definitions, but different possible causes.

My assumption is that your cylinder 6 misfire code was P0306, and the persistent misfire code was P1315, but if not, please clarify.

Thanks!

Don

 

Don,
I've already deleted the codes.
:-(

BTW: I was being facetious about the exasperation I expressed in the subject line.

I'll know better next time!
:-)

Of course, it's now warming up around here so the Jag is happier in the 'balmy' mornings. But, I see a clear day on the forecast and that means cold, so I'll just have to scamper out and fire it up for a short run to see if I can get those codes back!

 

Just did plugs on my Ex X300, and I noticed the coil wiring loom is getting "crispy", but the car is fine.

Crispy is a V12 well known term, and reeks havoc on the real engine.

I will replace that loom when next I lay hands on that car.

Check yours carefully, as you have to unplug it to do the plugs, and if its "sounds" crsipy, that may be an addition to your misfire source. Look REAL CAREFULLY at the section at the rear of the engine, where the loom bends to come out of the Plastic coil cover, that is the weak point on mine.

I run NGK plugs, BCPR6E, and always have without any issues at all.

 

Grant,
Thank for the heads-up, I'll listen up when I do the tune up.
(sorry about that, I couldn't resist.)

:-)

Charles

 

AHA, a sense of humour, you are set to go, enjoy.

 

Grant,
Being a Reluctant Mechanic anymore, the first tool I pull out of my kit is Humor.

Otherwise, the whole process tends to devolve into me feeling like The Inanimate Object has triumphed once again... and I am a sore loser.

Reluctantly yours,

Charles

 

So I changed the plugs, and the coolant sensor and the air filter. I'll have my real-life mechanic do the fuel filter since I hate getting gas dripped on me. :-)

The miss and lowered gas mileage remain.
:-(

But, I have NOT changed any coils yet.

Also, when I pulled the plugs, number 4 had oil puddled up around the top of the plug. Huh? Where does THAT come from? What DOES it mean?

And, all but #6 plug had a brown 'burnt' looking ring on the porcelain just above the 5/8" hex. Maybe someone had changed #6 plug but not the others.

And, I didn't know that the coils had gaskets under their heads. They were brittle and fell into multiple pieces. So I cut some out of the same thickness of paper-type gasket I had a roll of on the shelf.

Lastly, the wiring harness didn't crackle or evidence any 'crispiness'. Whew!

So, now I am thinking of getting the LHE1510AB# coil for #6 (which the OBDC codes said was the culprit) from sngbarratt.com

And, I'll have my mechanic put in the fuel filter.

 

Well done.

That oil in the hole is from the spark plug tube seals, mainly.

Some report the camcover itself "corroding" at the face of those tubes, where the seals sit, but I have not had that with mine.

When I did mine, I used a good smear of Hi-Temp RTV on those plug tube seals, and also at the "D" section of the outer gasket, just to be sure.



#3 are the culprits in question.

 

That brown burnt ring on the porcelain is known as Corona Stain and is typically not a problem. See this TSB from Jaguar:

Corona Stain on Spark Plugs

As far as we know, that's the best coil for your car. Just confirm with SNG Barratt that it is Made in Japan as were the original coils.

For the record, a malfunctioning coil is one possible cause of a misfire code such as P0306, but it's not the only possible cause. Here's a snip from the Diagnostic Trouble Codes Summaries guide that shows some possible causes of the P0300 series of codes:




Cheers,

Don

 

Grant,
Thanks for putting my mind at ease on the oil puddle stuff - I figured that it could only be coming out of the cylinder itself since anywhere else would have to have been some catastrophic and easily seen problem. :-)

Don,
Gee,thanks, you've put my mind at unease with the possible directions to go. :-)

No, really, that's rather helpful.

The miss is persistent, but I'm not getting the CEL at all. So, I need to check my OBDC codes again to see if something is lurking.

I see that one of the causes could be 'fuel pressure is low' - well, I haven't installed the fuel filter yet, and my guess is that it is stock. Gotta get that done!

So, it's "next things next"!

Thanks!

 

Chucck, #4 spark plug well seems particularly prone to corrosion and deformation judging from the five I've inspected. You'll find some pics of what is likely going on here: https://www.jaguarforums.com/forum/x...thread-163891/

 

Persistent misfire #6
So, the list for P0300 now applies for sure.

Time for the fuel filter.
If no fixie,
Coil for #6

Thanks to all!

I'll keep you updated.

 

Chuck,

I can't recall if you've tried this already, but before you buy a new coil, swap the coils for cylinders 6 and 5 and see if your P0306 code becomes P0305. If so, buy the new coil. If the code stays at cylinder 6, you have more diagnostic work to do.

Cheers,

Don

 

Don,
What an elegant way to troubleshoot!

Thank you.

I'll do it today.

Charles