Just a reminder, that there is no easy way to bench test these, you'd need an oscilloscope and a rather involved setup.I don't think we had good quality coils since QYL stopped making them, the Jag coils are stupid expensive, if you go the replacement route, you want the coils to have that plastic tab in the resin and preferably a brass insert, from my experience, these seem to last best. Occasionally you may be able to find new used Lucas coils on eBay which are always worth getting, they have a green Jaguar sticker on them.
Alternatively you may chance it with any "premier" coils that are available locally but be aware that they may randomly fail every now and then. I don't think I had a full set that lasted together for longer than 8 months and I've been using QYL coils now for many years(two failed but only because one got mechanically trashed when an "exploded spark plug impacted it and another died cooked in oil that leaked from an oil seal)

PS
Its always the coils.

 

@katar83
Well it certainly has been a combination of many things.
When you said to me IT IS THE COILS at that point the coils that are currently in my car were in my car.....
and the car was stumbling differently and running rich.

I then swapped them after you said that.
and i had no difference.
I then swapped the MAF, fixed a vacuum leak, replaced the IACV.
after replacing the MAF the car was running better, but not had a different style of idle issues.
it was no longer running rich and idled better, was no longer stalling on me.

and then now i swapped the coils back to the originals that were in the car and it runs well.
so it seems to me the MAF was the problem. amongst likely other things.

the original coils i had in the car are running fine now and those are the ones i had in when you said it was the coils.

 

hopefully final update
so now i discovered i was back to having one part of previous issue.
car was struggling to stat and not holding idle when cold.
I was now confident this was coil #2 as that was the one that read 11.5Mohm.
it seemed to have trouble when cold but then once it heated up it was getting into an acceptable resistance range.
swapped that to a low resistance cheapo and now the car runs fine.
the low resistance is much less of an issue and only seems to cause the idle issues when multiple plugs are in the same situation

a coil with too high resistance causes voltage issues and trouble sparking.
if the coil has too low resistance the problem will get worse as the car warms up.
if it has too high resistance it may get better as the car warms up.
the resistance in the coils will change as they heat.

so to reiterate. People say that you can't accurately bench test these so its may not be fail safe. the resistance my test ok but still have an issue. especially as it changes as they get hot. however, if the resistances are wrong, YOU WILL have issues. so it is still worth testing.
could save time and headache for sure. I was using known good replacements. (took them personally from a running car i had been driving. so thought they were ok. after testing them this way i knew they were wrong and was able to tell which one of my original set is also bad.
primary resistance (both connector pins) look for something 1 - 1.5ohms.
secondary resistance (one connector pin to electrode surface) look for 7.5 MegaOhm (some say kilo ohms but my multimeter only read it when on mega ohms)

I had 6 in my car (cheapos) that read a low 1.1Mohm secondary resistance and my idle was very unstable all over the place and worse as car got hot.
I replaced them with others (that were previously in my car) 5 of these read 7.5Mohm secondary whilst one read 11.5 (too high).
car seemed to run well, but then i realized i was having trouble starting and car could not hold idle when cold. this was the issue i had previously.
i have now put one of the low resistance coils in place of that one and car is running well.
i have ordered some good used OEM spares and will replace this one.

 

Oh i've forgot to write up. While my car seats headless (some bolts snapped so had to order a set) i've met that guy again as he wanted to connect my IDS just for routine check and marry the spare fob. So we've got a time to swap his coils with mine used 94 factory set and see how it runs. It runs absolutely same smooth hot or cold with no misfire. His coils are Lucas with small green stickers with Jaguar p/n and no black "made in Japan" labels with date codes of 20ish weeks of 2002. And i've checked the resistance on them. All 6 are like 0.9 ohm primary and infinite on secondary both ways just as all 10 Jaguar coils of 4 different types i have. So most likely original coils do have some suppressor schematics inside which cuts the secondary and brings the resistance test useless. Also i've found some old threads on Jag-Lovers forum where people discussed the smaller 0.030 spark gap as a measure to extend the coils life with some positive results achieved.

Still thinking about how come the Jaguar coils are that weak? Many over plug coils on other cars run for years even being a duplicates. Might be a really the spark gap choice is wrong? When i took off my cam cover i've found one interesting thing - cylinder 1 and 6 coil wells are not round inside and and inner and outer rims are not flat.

At the first sight i thought it's a paint peel but no. It looks like a sleeve pressed or welded into the well and it is badly distorted plus there are some carbon or oxidation deposits seats there. And it is exactly where the contact rod spring in the plug boot meets the coil. For me it looks like the spark damage. Good thing i've planned to replace the cover as mine is very ugly outside so i've bought the replacement in near perfect condition.
So might be the whole engineering on coil is a fail. I might be a beginner in an aged Jaguar world but i've seen pretty much a lot of other COP systems and most of them either keep the coil outside the cover reaching the plug with a long reliable isolated boot or done with much smaller diameter and also well isolated. Like this

BTW it's a UF553 coil for Ford/Mazda 3.7 V6 engine. It has very similar length of 133mm and also a 2-pin. They are cheap even being an OEM Motorcraft so probably i'll try to test one or two of them as a substitute...

 

Coil on plug resistance, straight from the "horse's mouth", eliminates the guesswork
See attached -

John Herbert
1996 XJR

 

did it read infinite resistance when set to mega ohms?
also keen to hear of any suitable substitutes.

ah yes valve cover issues.
i resurfaced my valve cover when i did repairs and flattened it out. they were out of round and wavy not flat.

 

unless i missed t, unfortunately does not show the secondary resistance which in my case appears to be the issue.

 

Yes it did.

 

Ran across the coil specs sheet on a Wells manufacture " equivalent " for the X300 and the oil output was 35,000 volts vs. 30,000 volts as the standard so would question finding an alternative coil beside the " Made In Japan " originals or phony copies still saying made in Japan

There is the thing of the valve cover being electrically isolate in theory by the plastic top hat shouldered bushings on the 13 valve cover mount bolts , but..............................it's 35,000 volts

The cleaning of the large ground strap on the starter mount bolt to car's left chassis rail , paying attention to the rail cleaning , seemed to resolve a mysterious engine regulation issue years back from reading

My thoughts were since more than one signal can be present in a wire at one time and the ECU operates on DC and not stray / polluted AC induced by a timed spark jumping to the valve cover ................

This more than one signal in a wire is how the old school vacuum tube guitar amplifier works as a simple to understand going through in these 2 videos

in the guitars example this is a mono signal and not stereo left and right signal

 

OK. Got the head installed, everything went well, no parts lost, no parts left (except replaced), timing is correct, valve clearances are .012-.014, compression is 160+ all 6, cylinder leak test passed, starts right away, fuel pressure steady is close to 40 running, no vacuum leaks. Engine feels somewhat stronger for sure. But still shudders hot (by the ECU data it's around 185 when sits idling). Like not even misfires but feels like and idle adjusting on carburetor but rpm is steady and i see the IAC stepper value is at 39. And P0300 still pending while P0313 and 0314 went away. And it still hesitates on throttle blips. Not bursting the rpms like normal high compression DOHC must do. It chokes a while and only then takes a throttle. Obviously, something is not right. Might need more driving to adjust or two days of city start-stop and some highway is enough? I do have spare ECU from 95 VDP with same t493 recall sticker part number written (was lucky to have it just for $90) and i swapped it earlier despite it is told the ECU is rare to fail if no corrosion signs found but it was worth a try. After the throttle adaptation and oxygen sensors orientation there were no differences after initial day or two driving. And there are same shudders with Andy's bracket or stock on all three CKP i have (OEM, Walker and some eBay) and with all three sets of coils i have (i've mixed them yes and i have one set confirmed running well on other car). Out of ideas for now.

 

it really does sound like coils so i dunno.....
hows the injectors?
maybe one is a little leaky?
or lazy?

 

At last we have P0443 on EVAP. Some progress hopefully. And the engine restarts bad on hot. Either need 2-3 attempts or chases the idle 2-3 times then keeps rpm steady. This might be a separate issue as i've installed the Andy's bracket again and i had the same when i installed it for the first time. Thing is i rarely switch off and then on while it's hot. Now while i am working on it i've found this hot restart thing.
OK, will put the original bracket back to check the hot restart while the purge valve coming (good thing it's available). Interesting it's a Siemens unit with VW/Audi logo and some VAG looking part number but internet brings nothing on it.

As for the coils... I dunno too. I have 18 of them and at different combinations it runs same. Injectors are rebuilt Lucas from reputable company. Checked them earlier - no leaks, spray well. Swapped them between the cylinders with no luck. BTW, connected the oscilloscope to the injectors and coils - graphs are pretty same between cylinders. So either ECU is not cutting itself or my very bacis device doesn't have enough reference to detect.

 

Found this elsewhere

Evaporative Emission Control – P0443
Model:
Jaguar XJ Range 1996, 1997
Complaint:
Fault code P0443 will most likely be set due to an EVAP purge control in the valve circuit fault.
Remedy:
Switch off engine.
Check the harness and connectors to ensure they are in good condition and are reliable. If they are faulty then either repair or replace and go to step 6 of the test below.
Disconnect the EVAP valve if no fault is found and go to step 1 of the test below.
Test:
Check the harness continuity PI 130/001 is correctly wired to PI 119/005. If this gives a positive result then go to step 2. If the circuit is open then find and repair the wiring fault, re-connect the harness and go to step 6.
Check the harness continuity PI 130/002 is correctly wired to PI 105/006. If this gives a positive result then go to step 3. If the circuit is open then find and repair the wiring fault, re-connect the harness and go to step 6.
Check the harness insulation PI 130/001 will complete a circuit to ground. If this gives a positive result then go to step 4. If the circuit shorts then find and repair the wiring fault, re-connect the harness and go to step 6.
Check the harness insulation PI 130/002 will complete a circuit to ground. If this gives a positive result then go to step 5. If the circuit shorts then find and repair the wiring fault, re-connect the harness and go to step 6.
Check the harness insulation PI 130/001 will complete a circuit to PI 130/002. If this gives a positive result then go to step 6. If the circuit shorts then find and repair the wiring fault, re-connect the harness and go to step 6.
Clear the fault. Then in order to check if the fault code has been cleared perform the service drive cycle. If this gives a positive result then stop. If the fault is still present then go to step 7.
Repeat the diagnostic procedure. If this now omits a positive result then stop.

 

It's from electrical diag manual. I've checked the circuit. Control line from the ECU is OK. Power OK too. BTW purge valve got the power from the ECU controlled relay together with injectors, MAF, EGR, canister close valve and fuel tank pressure sensor (if they are installed). Also two powers come back to the ECU from here so ECU definitely knows if relay brings power or not (relay have been replaced BTW and i see the power rather same on injectors and on the alternator output. On coils too however it's a different relay.

PS. I wonder how the voltmeter on the cluster brings the measurement. If it's just what the cluster see on its power feed or is it brought from somewhere with serial data? I might be over suspecting now but it looks like when the engine shudders more deep (it does usually like "wrrrrrrrrrrrr... blip wrrrrrrrrrr" but sometimes it makes more like real misfire for a second) i probably notice that voltage drops too and then gets back to normal. But it doesn't look like i see the voltage drop on coils or injectors in that moment.
PPS. Replaced back the original CKP bracket. Hot restart issue went away.

 

I went through a similar experience with faulty idle and misses on acceleration.
I changed out and checked everything. Nothing worked.
Finally I bought a new ECU and plugged it in and it solved all the problems.
Haven't had any issues since. My XJ6 was getting scary to drive.
Starting from stopped it would sometimes stall pulling into traffic.
Glad I finally solved it but at great expense.

 

I have spare ECU. On both things are same. Same P0300 at least. But might worth a try to swap them one more time after i got my new purge valve.

 

Okay. Two weeks later.
After i have new EVAP valve installed P0443 hadn't come back. Installed other ECU i have but it still brings P0300 and some P0301 (which both i see since i have the car) as pending (like these codes are never light the CEL but you can see them pending in the memory). There is absolutely nothing wrong with Cylinder 1. I've put different coils and plugs, i swapped the injectors several times, i've load tested the wires to coils and injectors. Same 160+ compression on all 6 jugs. Timing is set with the tool on head replacement. Car starts instantly hot or cold and idles pretty much smooth cold and hot on D. Hot on P shudders occasionally and somewhat not constant. Like it's actually not a failure but the way the ECU controls the engine. Might be its that EGR "cleaning cycle" they told in T493 bulletin. Might be it's because of 10% ethanol in the fuel (i couldn't find any premium non-ethanol around here to to a deep research) but i've noticed that on Sunoco 94 it shudders likely less than on 91 premium i usually use as far as on ethanol free premium i filled upstate NY once recently it also looks to be less shudders. So except of this it runs well and i consider it as a feature from now on.

PS. And it still doesn't like the Andy's bracket. Hot start is bad on it.

 

quite likely it is related to ethanol and octane.
now i know that US uses a different octane rating to us over here,
but to my understanding the Jags should not be run on ethanol and should be run with 95 RON (91 AKI) or higher.
personally i only run mine here with 98 RON (93-94 AKI)

from my understanding as ethanol contains oxygen it can lead to lean running if the 02 sensors and ECU does not correctly adjust for it.

 

I can say no car from 20th century shouldn't be run on any ethanol percent fuel. But here in US it's not that simple to find the non-ethanol gas. It's always "may contain up to 10%" on standard pumps and it is considered aside of seasonal degradation and water absorption or carburetor internals damage these 10% have not much influence on older engines work in common. And also people said like the more octane the less ethanol might be actually in the gas. But i know for sure that Wawa premium smells different than Sunoco.

PS. And i still think there is something special for ECU firmware for natural aspirated 95 4.0. Might be for North America only but something it is. And that's why they have paused R493 specially for 95 and then bring a revised T493

 

i wouldn't say the more octane the less ethanol.
ethanol actually has a higher octane content
hence E85 being race fuel. 85% ethanol. 102-108 RON.
its more a matter of how much it can destroy certain rubbers and the change in the way it burns as opposed to just octane number.
thats a shame bout the fuel over there.
here we have 5 major types of petrol.
regular 91 RON
then we have E10 which is 91RON + 10% ethanol increasing its RON to 94
then we have 95 RON
then we have the premium 98 RON
and lastly we have E85 (only at a few service stations here and there) only good for cars that are set up and tuned to run it.

only the E10 and the E85 have ethanol. the standard 91,95 and 98 are not allowed to have any.


and yeah can't comment on NA ECU's as over here we don not have EGR