[v12-engine] resistance values -- spark plugs wires

V12-Engine
1

Gentlemen:
I had recently posted about a cold-start problem with my
6.0L.

http://forums.jag-lovers.org/av.php?1570882n77

Many hours of tests in the garage, yet, the problem is hard
to replicate and appears to have gone away. Perhaps gas
formulation changing to winter mix helped masked the
underlying issue or it was a bad connection that was
‘‘fixed’’, a least temporarily.

Anyhow, I had done a tune-up 2000 miles ago and had replaced
the original spark plugs wires with new aftermarket ones. A
local mechanic advised me to check them and I did so by
measuring the resistance – they all ranged from ca. 450 to
1200 Ohms, the longest being the highest in value.

But, when I check the old ones, they were all in the kiloOhm
range – from 4 to 6.0 kΩ.

Thinking that the higher resistance of the old wires was due
to age, I then went to the local autoparts store and tested
another set of brand-new wires for an unknown 4 cylinder
engine – they were also in the 3-4 kΩ range.

After this long rant, my really simple question to the forum
members is – what is the normal range of the resistance
values of the spark plugs wires on a JAG V12?

Hope someone would be able to help.

Best regards,

Steve–
'95 XJS V12 6.0L, saphire/tan
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2

In reply to a message from sbobev sent Sun 30 Dec 2012:

First of all, the bad part is that I have no spec for plug wire
resistance for the V12. But, overall and in general, The rule of
thumb that I have heard for 40 years, is that resistance should not
exceed 10,000 ohms per foot. the resistance of your new wires is a
bit on the low side. Low resistance should not cause any running
problems, but sometimes low resistance wires, usually solid core
wires with almost no resistance, will emit a lot of radio frequency
interference (RFI). This usually is more of an issue with radio
reception than anything else. If your radio works OK, probably
everything else does too. It is possible, but pretty unlikely this
could interfere with the ECM.–
Happy Motoring!
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3

In reply to a message from sbobev sent Sun 30 Dec 2012:

Hi Steve

I have a genuine new set of leads I picked up as a spare and are
still in the packet. I will check the resistance of some of them
and post the results . I am sure the higher resistance will be to
reduce electrical interferance and often low resistance cables
would have resistive type of plugs.–
The original message included these comments:

members is – what is the normal range of the resistance
values of the spark plugs wires on a JAG V12?
Hope someone would be able to help.

–
95 XJR6, 94 XJS 6.0 coupe, 04 XK8 ,99 Ka
Croydon , SURREY, United Kingdom
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4

In reply to a message from sbobev sent Sun 30 Dec 2012:

Steve,

Interesting question. I went to my bins and pulled out the
wires, measured them for you

A1, 3.2K, 12’’
A2, 2.7K, 9’’
A3, 2.5K, 9’’
A4, 2.6K, 9’’
A5, 3.4K, 13’’
A6, 3.2K, 13’’

B1, 0.0K, 17’’
B2, 3.0K, 11’’
B3, 2.0K, 7’’
B4, 2.1K, 8’’
B5, 3.5K, 13’’
B6, 3.6K, 14’’

COIL WIRE TO DIZZY 1.9K, 7’’

These are blue Magnecor Electrosport 80 cn20-136t metallic
inductance emi suppressed conductor, all silicone

About 6 years old

I like the reading on B1, gotta laugh, may explain the rough
idle

Cheers

Doug–
The original message included these comments:

local mechanic advised me to check them and I did so by
measuring the resistance – they all ranged from ca. 450 to
1200 Ohms, the longest being the highest in value.
But, when I check the old ones, they were all in the kiloOhm
range – from 4 to 6.0 kΩ.

–
1987 XJ-S, 1988 XJ-S Tremec TK500. AJ6 Torque kit
Toronto, Canada
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5

In reply to a message from Repairman sent Tue 1 Jan 2013:

I have a brand new sealed pack of 6.0l jaguar plug leads
part number LHD1509AA. These must of been old stoc but wer
new as I have just opened the bag to test these. I Have
tested these on a fluke / Philips scope meter .

A 8.8k. B. 2.9k. Coil leads A & B
A1. 3.4k. B1. 3.4k
A2. 4.7k. B2 5.2k
A3. 4.8k. B3 3.7
A4. 2.5k. B4 3.2k
A5. 5.2k. B5 3.4k
A6. 3.7k. B6.4.3k

This test proves 2.5k up to 8.8k. And would have been a
good test if they had just been made but this is the best
test I can do . Remember as long as the leads are not over
about 30k ohms resistance should not do much as no
current flow = no voltage drop until the plug sparks .

Ps your 0.0k must be your meter was on the wrong range or
you mean it read open circuit ? In which case should
display. OL. = open–
The original message included these comments:

I like the reading on B1, gotta laugh, may explain the rough

–
95 XJR6, 94 XJS 6.0 coupe, 04 XK8 ,99 Ka
Croydon , SURREY, United Kingdom
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6

In reply to a message from 540itouring sent Tue 1 Jan 2013:

540:

OL it is, my mistake.

I’m still laughing that its a dead wire

Cheers–
The original message included these comments:

Ps your 0.0k must be your meter was on the wrong range or
you mean it read open circuit ? In which case should
display. OL. = open

–
1987 XJ-S, 1988 XJ-S Tremec TK500. AJ6 Torque kit
Toronto, Canada
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