Another automotive technician eats his words

I had been trying to track down a random miss in my 89 XJ (4.0 Renix, auto) for the past year ... yeah, it was that random.
Then it finally became somewhat regular with the engine cutting out at
highway speeds for a second or two and just a fairly regular miss in between at all speeds.
Replacing the fuel filter stopped the high speed cutting out, but it took a full ignition tune-up to eliminate the other miss.
Now a word of automotive history for those that have never set points:
Before the EPA started writing laws (though they are not a legislative body) engines used copper conductor plug wiring from coil to distributor and distributor to plugs.
Resistor plugs were used only if the vehicle had a radio (AM is very susceptible to ignition noise) which gave the same voltage to all plugs within +/- 1% (15000-17500 volts average at the plug and 10% less at the plug gap with resistor plugs).
or
Resistor cables were used with non-resistor plugs which gave a 10-15% voltage variation at the plug gap (no loss to speak of in the plug) depending on the cable's length.
Today, thanks to the EPA,iirc, we are stuck with resistor plugs and cables on all engines except diesels.
So you've got a serious variation in available voltage at the gap to fire the fuel/air mix with.
Can anyone else see how this can affect mileage, performance, or even cold weather starting?
I was told by a certified automotive technician that running copper core cables would destroy the XJ's computer and engine management in seconds.
I put a set on today and my 4.0 runs better than it ever has: no missing, faster starting, smoother idle, (is it running???) and I'm using less throttle opening to maintain a speed even up a hill.
Now if I just find that "expert" again . . . .
Budd
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Budd Cochran wrote:

Might try that myself. I did wonder what would happen to the coil though if it had to discharge too much current at one time. That's what the resistors slow down. Though I doubt your 89 has the same fiddly bits as my 93. Probably time for me to call in on that lifetime cap/rotor and wires waranty I picked up 14 years ago. :)
My first lesson about plugs and wires came after making my old C-10 chevy's 305 small block all nice and cool looking. Ran all the wires evenly using some neat aluminum wire clamps I picked up at the flea market.
Looked like a million bucks.
...ran like a steam powered turd...
Induction, bad mix of short and long runs. Still have the wire holders though. They are holding screwdrivers on my workbench and one found a new purpose in keeping vac lines off the header.
The 4.0 is interesting though. The wires are mostly similar in length. I wonder what would happen if I custom built a set of all equal length?
--
DougW



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On 3/23/2015 7:32 PM, DougW wrote:

I have an older brother that was an electronics tech in the Air Force for 26 years. He taught me that electrical/electronic circuits will draw only the current they need unless they are shorted out ... then the rules go out the window.
If you can find a way to connect a high performance coil to your system it'll probably work fine and hold up longer.
Stock coils are built to handle the demands of a lot of heating due to the overall resistance of the circuit (resistance makes heat ...just look in your toaster in the morning) so dropping the resistance will reduce heating.
Funnily enough, the ballast resistors were originally to keep points from burning up under 12V power, today they limit current to the engine controller to keep it from frying.
Equal lengths are no guarantee of equal voltage to the plugs since most resistor cables are rather fragile, which is why they go bad so fast compared to copper conductors, which can last over 100,000 miles.
You would need to find what is the shortest length you could run from the cap tower contact that's the farthest from it's cylinder.
On the 4.0 I think it's #6.
A buddy of mine way back when decided to replace the plug wires on his Ford 312 police Interceptor engine (56 Custom 2dr) then he taped them together because he didn't want to buy new separators.
In his case the engine wouldn't even start.
Budd
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Budd Cochran said:

Years ago I replaced the resistor wires with copper core with excellent results, but when I'd pull into the driveway, the TV in the living room would go whacko.
--
Dale Beckett

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Dale Beckett wrote:

Yep, either 1 or 6. 6 is easier to get to since 1 is burried under the f---ing ac compressor.

I imagine. :)

Now TV is all whacko. ^_^
I was amused by what the old spark strength checker would do to my old TV.
Still though I'm thinking it's time to check the plug wires anyway. Eventually they do break down and get too high a resitance for a good spark.
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