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