Ignition coil and engine heat

XJ
1

Good evening everybody,

after well over 12 years during which the Jag never let me down I experienced a sudden and intermittent problem last summer. Every now and then the car would lose power, sometimes drastically, hardly pulling away from a stop, sometimes less with just a feel of being restricted. Everytime the engine went back to work after some time and there was no tendency of the whole thing getting worse. There was no problem during winter, but the thing started again some weeks ago …

As the phenomenon only occurs with higher ambient temps it was general consensus on the list that it might be either the coil or something weird going on in the carbs. As you might have guessed I started with the easy and inexpensive solution, bought a new coil and fitted it last Saturday.

The good thing first: even though access (without removal of the air filter box) is somewhat restricted, replacement was straightforward and the car now starts and runs just fine. I even did a 20-mile test run with temperatures in the 80s and, at least for the moment, there were no more issues. Touch wood that the coil really was the culprit.

Now the strange thing: running on the new coil water temps were significantly lower than before. Before the swap the car would run at “n” of “normal” and with higher ambient temps and either serious action (motorway + 65 mph) or city traffic rise to vertical and a needle width above. With the new coilthe needle was far right from the “n” during regular operation and approached it only in city driving.

Most certainly, some fiddle factor is involved - in fact, on the first run the water temp needle wouldn’t move at all. Only upon opening the hood and shuffling things about it went back into operation. Apart from that, could a coil ever influence operation temp of the engine? Plugs, sure, distributor and advance mechanism, sure, but a simple coil?

For the facts: I replaced what appears to be the original Lucas coil with a replacement part that was sold as “Lucas” and has a paper sticker on the mount reading “Lucas”, but no “Lucas” embossed in the black plastic top. It is much smaller and has inverted + and - connectors. The coil is connected to a 1-2-3 ignition, as was the original coil.

Final trivia: I’d like to keep the original coil which still looks good. Beyond the standard test measuring resistance between + and - and between primary and secondary circuit, is there any generally accepted procedure to test and exclude internal failures that may or may not result in malfunction?

As always, thank you all

Jochen

75 XJ6L 4.2 auto (UK spec)

2

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I think the best idea is to measure actual engine temp with an infrared thermometer, Jochen - and compare it to the gauge reading…

There is no way of telling whether the temp reading before the coil swap was correct, and the latter reading correct - after the ‘shuffling things around’ bit. But it is rather important to verify the temp anyway - and the change may be unconnected with the coil swap; another fault may have sneaked up on you…?

Incidentally; the original coil was not intended for the ‘1-2-3’ ignition - nor likely the aftermarket coil fitted. (Originally a 6V coil was fitted with a resistor bypassed while cranking). However, most coils will work OK - or engine will show its displeasure…

Frank
xj6 85 Sov Europe (UK/NZ)

3

Jochen,

Clean the contact at the sender and make sure the plug makes good contact.
If there is non difference, run a cable directly from the sender to the gauge.
If still no difference, either its a coincidence and your sender, or gauge, or even your thermostat have a problem, or the new coil has extraterrestrial properties…
Measuring temps with an infrared thermometer as Frank suggested would shed more light.

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Thanks Frank and Aristides,

very happy not to be surprised by some “well, didn’t you know that the voltage of the secondary circuit affects the speed of …” or something like that I never heard of before:-)

So yes, it should be attributed to some coincidence of failures - or simple changes - in the setup. Two years ago I swapped the t-stat for a 88°C part to raise operation temps and ever since that I had quite perfect water temps. As I had measured the new t-stat in a boiling water pot and the guage subsequently indicated corresponding operation temps under regular conditions I didn’t care to directly measure temperature - unfortunately, as for this reason I don’t have any data to compare.

BTW, Frank, you’re right - the original coil was not designed for use with a 1-2-3 ignition. However, the maker of the ignition only requires “stock- or High Energy- coil primary coil NOT below 1,0 ohm”. Too lazy to check it out I assumed that - if the original coil worked well for over 15 years an identical replacement would do the same. Unfortunately, I first was wrong in that the original coil has a resistance of 0.8 ohm between + and - and I just found on their website the statement

“Note: We hear a lot of complains from our customers about the fake “Lucas Sport” or “Lucas gold” coils, better don’t use these coils.” https://123ignition.com/support/ last visited 07-15-2020)

As I wrote in my OP I’m fairly sure that the coil I installed is such a fake; so I’m keeping my fingers crossed and preparing for another swap; 1-2-3 ignition recommend Bosch Blue or Beru ZS106.

Anyhow, I will address the temp sender contact and measure temps with my infrared thermometer - will report back!

Thanks again

Jochen

75 XJ6L 4.2 auto (UK spec)

5

+1 on the fake gold coils… keine gute Ware. Mine worked, but it wasn’t any good for starting both cold and hot. Also, the plastic developed a crack and it soon began to leak. However, it did run well, so not to worry for now; I‘m sure you have a spare somewhere-?
Of course it will run with the 123, as Frank says, no adverse symptoms; you should be good.

When I exchanged my wiring harness, my oil pressure dropped a few psi. Also, as I also swapped the temperature sender, the temperature rose by 5-7°. I put in a resistor that was original to the donor engine, from Jaguar. Nothing to worry about, I think, and since spark is spark, you probably just moved a wire in the process and this got rid of some corrosion… but do also check your coolant level. And unlikely, but maybe the distributor was retarded in the process. If you don’t have and adverse symptoms I would keep motoring.
Good to hear the new coil cured the running issue.
By the way, is your oil filter housing blue, green or grey hammertone?:slightly_smiling_face:
Best
David

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Electronic ignitions are sometimes vulnerable to coil specifications, Jochen - and makers may issue coil specifications accordingly. However, this usually is to protect the electronics rather than the coil itself.

Coils are simple creatures in concept, but with a wide variety in execution - as shown by the varieties in primary coil resistances. Coils will work over a wide range of applications…

As an aside; the actual size of a coil reflects the ability to dissipate heat…

Frank
xj6 85 Sov Europe (UK/NZ)
**

7

Nowadays, in a sense, anything you buy that’s branded “Lucas” is a fake.

Lucas still exists but it sold-off the automotive parts division about 25 years ago…together with rights to use the Lucas name. I can’t remember the name of the new company but I’m 99% sure that label-engineering is the primary form of business; I’m not sure if they actually manufacture anything themselves.

Years ago I went thru hell and high water with Lucas branded/labeled coils on my XJR…but that’s a long story and not pertinent here.

I’m on my first two sips of coffee and am too foggy-brained at the moment to comment on the technical aspects of this discussion :slight_smile:

Cheers
DD

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I think the company is Holden in the UK, Doug. Paul.

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Thank you all,

right, Doug, I knew that Lucas hasn’t been producing own parts for a long time, but would have thought they make better use of their brand good will in the classic car world and franchise the green sticker only for stuff better in line with original specs.

As you wrote, Frank, the main problem in operation is not the coil, but the risk of consequential damage in the ignition and that’s exactly the gist of the warning expressed by 1-2-3. Then again, 15 years on 0.8 ohm haven’t done any harm to the ignition, so I’ll keep an eye on the coil and the starting and running properties. If the wannabe-Lucas coil gives any kind of trouble I’ll get a Bosch blue coil.

As per David’s remark, first of all I’d be more than happy if the coil, for the better or the worse, cured the original engine running problem. Summer time will tell.

Best

Jochen

75 XJ6L 4.2 auto (UK spec)

10

I have BoschGT40R coil in my XJ ~ 1.1ohms primary resistance. I run this without the external resistor. The 123 words suggest not less than 1 ohm from memory. No dramas over the last year since fitting the 123. There is also a GT40 that includes about 3 ohms resistance. FWIW. Paul.

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“Note: We hear a lot of complains from our customers about the fake “Lucas Sport” or “Lucas gold” coils, better don’t use these coils.” https://123ignition.com/support/ last visited 07-15-2020)

Interesting. Not sure whether they are saying the “Lucas Sport” or “Lucas gold” is fake, or that some of the “Lucas Sport” or “Lucas gold” coils on the market are fakes (while others are original).
I’ve been driving my Series 3 with a “Lucas Sport” or “Lucas gold” coil for the past eight or nine years and have no complaints about it. The rest of my ignition system is original Series 3 though.

Regards,

Andy

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The warning from the ‘123’ relates to the use of such coils with the ‘123’ set-up, Andy - not specifically related to the quality of the mentioned coils. The original S3 CE system is likely more forgiving…

Frank
xj6 85 Sov Europe (UK/NZ)
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