Spark plug wire testing, resistance values?
eraser
got replaced by a set of Ford Racing 9mm plug wires) but I don't know
what the limit is to determine if a wire is good or bad.
The highest resistance values I got was 11.76k ohms
The lowest was 7.3k ohms
I tested a defective Ford Racing wire (the #2 plug wire had a conductor
strand jutting out from the plug boot - causing a misfire each time #2
fired) and it was 2.00k ohms.
So what kind of reading tells me that the wire is brand new and not
defective, and what kind of reading tells me the wire should be
replaced?
--
---------------------------
charlie
era...@cybernex.net
http://www2.cybernex.net/~eraser
"There's no such thing as too much torque."
Robert Jerin
--
"Human beings are the only animal that allow their children to come back
home"
Bill Cosby
eraser <era...@cybernex.net> wrote in message
news:398DDC17...@cybernex.net...
> I've been testing out my Motorcraft 8mm spark plug wires (the ones that
> got replaced by a set of Ford Racing 9mm plug wires) but I don't know
> what the limit is to determine if a wire is good or bad.
>
> The highest resistance values I got was 11.76k ohms
> The lowest was 7.3k ohms
Ford calls for 7k ohms per foot for many engines. An old rule of thumb was
6k ohms per foot and no more than 18k ohms. These are TeleVision Radio
Suspression (TVRS) wires as required by manufacturers for many years. These
reduce interference with radios and other communication devices.
>
> I tested a defective Ford Racing wire (the #2 plug wire had a conductor
> strand jutting out from the plug boot - causing a misfire each time #2
> fired) and it was 2.00k ohms.
>
> So what kind of reading tells me that the wire is brand new and not
> defective, and what kind of reading tells me the wire should be
> replaced?
To tell whether a wire is brand new or not has little to do with testing
resistance. Now defective yes, if in the case you see a reading over 18k
ohms then that wire could be suspect. The "racing" wire sounds like it may
not have been a TVRS type wire, rather it sounds like a "solid" core wire
thus the reading of 2.00 ohms. If an open had been the cause of a misfire
that would have shown as a very high resistance reading and not a low one
like you found. High resistance in plug wires is generally caused by
breaks in the conductor material of the wire and generally when that gap
exceeds the gap of the plug then a misfire results.
However you indicated that a "strand of conductor was jutting out" thus the
electricity took the path of least resistance to its ultimate destination -
ground via the head or manifold and not the spark plug as intended.
Bj
Allen Barnett
>
> I've been testing out my Motorcraft 8mm spark plug wires (the ones that
> got replaced by a set of Ford Racing 9mm plug wires) but I don't know
> what the limit is to determine if a wire is good or bad.
>
> The highest resistance values I got was 11.76k ohms
> The lowest was 7.3k ohms
>
> strand jutting out from the plug boot - causing a misfire each time #2
> fired) and it was 2.00k ohms.
>
> So what kind of reading tells me that the wire is brand new and not
> defective, and what kind of reading tells me the wire should be
> replaced?
>
***
Charlie - speaking as an electronic technician ... the resistance
you should get on a new wire is going to be dependent on the
length of the wire. Resistance adds in series and each inch or
foot of wire amounts to adding another resistor in series. So,
on a hypothetical new wire - if one foot measures 5,000 ohms -
two feet would measure 10,000 ohms - and so on. Longer higher -
shorter lower.
As to defective wires - one would be bad when it measures
significantly higher than it did the day it was new. I suppose
each manufacturer could quote specifications.
So far as automotive wires go and what I have read ... 30,000
ohms would be the discard point for the longest wire. But - a
wise tester would compare one wire to another and the ones 'out
of the ball park' could be considered bad.
--
Allen Barnett
eraser
reading of 1.77k ohms. Which roughly equates to 1.18k ohm per foot.
Thanks
"There's no such thing as too much torque."
Allen Barnett
>
> The wire was 18 inches long, and after repairing the defect, I got a
> reading of 1.77k ohms. Which roughly equates to 1.18k ohm per foot.
> Thanks
***
I would expect this to vary greatly between manufacturers, size
of wire, age - etc. There simply must be some resistance along
the wire for the 'principal of interference reduction' to work.
I don't know the design specifications.
--
Allen Barnett
Robert Jerin
--
"Human beings are the only animal that allow their children to come back
home"
Bill Cosby
Allen Barnett <allen_...@bigfoot.com> wrote in message
news:398EAEA3...@bigfoot.com...
The long time automotive "rule of thumb" for standard passenger car
application has been 6k per foot and not more than 18k for any cable. This
resistance is based on the need to use TV and Radio Suppression cables
(TVRS).
Bj
-Bodnar,B.L.
eraser <era...@cybernex.net> wrote:
>I've been testing out my Motorcraft 8mm spark plug wires (the ones that
>got replaced by a set of Ford Racing 9mm plug wires) but I don't know
>what the limit is to determine if a wire is good or bad.
>
>The highest resistance values I got was 11.76k ohms
>The lowest was 7.3k ohms
>
>I tested a defective Ford Racing wire (the #2 plug wire had a conductor
>strand jutting out from the plug boot - causing a misfire each time #2
>fired) and it was 2.00k ohms.
>
>So what kind of reading tells me that the wire is brand new and not
>defective, and what kind of reading tells me the wire should be
>replaced?
>
>--
>---------------------------
>charlie
>era...@cybernex.net
The resistance readings look "in range." A static test like this, however,
will not show whether the ignition wire is capable of operating under load
(e.g., if there's a punch-through in the insulation). The easiest way to test
this is to use the wire in the engine, wet the wire(s) with water, and run the
tip of a grounded test light about 1 mm above the insulation. Recall from
electromagnetic field theory that the strength of an electric field is
inversely proportional to the square of the radius of curvature of an object
-- thus, the test light's probe will cause a *massive* electric field to build
up by the tip whenever the ignition pulse is sent down that wire. If the
insulation's marginal, you *will* have a spark punch through the insulation.
I use this method, and I also 'scope the ignition system (www.aeswave.com has
nice 1000:1 ignition adaptors which allow one to use a general-purpose
oscilloscope as an ignition 'scope). On a good ignition system in pristine
condition, you should have a firing voltage in the range of 8 kV to 12 kV,
somewhat higher if you're using high resistance wire.
Cordially,
Bohdan Bodnar
AJDalton7
>tip of a grounded test light about 1 mm above the insulation.
B.L.,
A 12 v. test lamp?
Thanks,
Arthur
-Bodnar,B.L.
Correct. I learned this trick years ago from an ASE Master Tech who was
teaching a bunch of courses at a local junior college. When I have someone
complain that their engine runs rough during or immediately after a rainstorm,
this is the FIRST check I do before pulling out a 'scope.
Regards,
Bohdan
Mike Romain
Neat trick, I'll remember that one. Sure beats using one's finger to
test for leaks. ;-)
Mike
AJDalton7
Thanks,
Arthur
eraser
I6, 300 CID). I tested the wires and here's what I got:
1). 15.34 k Ohm, 9.44 k Ohm/ft
2). 23.5 k Ohm, 12 k Ohm/ft
3). 22 k Ohm, 11 k Ohm/ft
4). 13.2 k Ohm, 13.2 k Ohm/ft
5). 15.5 k Ohm, 11.63 k Ohm/ft
6). 18.91 k Ohm, 16.21 k Ohm/ft
Ignition coil wire: 7.95 k Ohm, 6.81 k Ohm/ft
He bought these wires about 2 years ago and had them still sealed in the
box - when I opened them today the silicone smell was still fresh. What
would happen if he used these wires? These numbers are significantly
higher than the Ford Motorsport 9mm wires.