Can bad plugs damage new wires in a short period?

irishalchemistirishalchemist Member Posts: 152
edited March 2014 in Mazda
As the title says. My plug wires died on my car a while ago (April). I changed them (they were original at 55K miles), but did not change the plugs at the same time.

Car still misfired occasionally, and a month or so later I changed the plugs. They were way over-gaped (max is 0.045", I was at 0.055+"). I also changed distributor cap/rotor. In any event, now every time it's humid/damp, the car seems to hesitate a bit in the morning. When it's dry/coolish in the morning it is a lot more responsive.

So after all this, the question. Could the bad plugs ruin the new cables in only 2 or so months?

Thanks in advance for any word(s) of wisdom,



  • vidtechvidtech Member Posts: 212
    you might want to examine the coil for cracks or carbon tracking.high secondary ignition resistance which occurs with bad wiring and wide (worn)plugs is hard on coils.
  • q45manq45man Member Posts: 416
    " I also changed distributor cap/rotor"

    OEM or aftermarket parts?
  • irishalchemistirishalchemist Member Posts: 152
    vidtech, thanks. I also thought of the coils, but wanted to get a second opinion. They are part of the distributor in my Protege, so I bet that if they need replacement I will have to replace the whole darned thing...

    q45, no, they are not OEM, and I also tought this could be the problem. They are NAPA (Echlin), which is a decent brand. In any event, I think I will order an OEM disty/cap set...

  • vidtechvidtech Member Posts: 212
    i like to use oem parts but i see nothing wrong with napa/echlin and seriously doubt those brands would cause you any problems.just stay away from the discount store stuff.
  • 0patience0patience Member Posts: 1,712
    Always, Always, Always and I cannot stress enough, Always replace the wires and plugs together on newer vehicles.

    what year, make and model?
    The answer to your question is yes.

    To help you understand, plug wires are high voltage lines, if you have a bad plug, think of it as a direct short. What happens to high voltage lines when they directly short to ground? They burn up. Follow?

    My personal experience with newer vehicles, on plug wires, coils, electrical and most sensors, it is best to go with OEM. Dist caps, ok with NAPA premium [brass contacts, not aluminum].
    NAPA has quality premium plug wires, but I have had far more success with OEM plug wires.
  • irishalchemistirishalchemist Member Posts: 152
    ...0patience for your reply. I rather get the 'personal experience' answer, which you certainly have, than the 'theory'. I have that too. I worked for years in electronics and have repaired things far more complicated than a car. But sometimes you can read books, and in practice things are just the opposite. And, I also suspected I had fried the cables. Just wanted to check.

    Also, in the case of over-gaped plugs, it's not exactly a short, but more as vidtech mentioned, high resistance. Since you need a certain voltage to get spark, wider gap means higher voltage, and that means that you are getting more and more current through the wire (it has 'constant' resistance). This all translates into more heat, and finally the insulation breaking up. As I said, I understand the theory...

    In any event, the car is a Mazda Protege '96 (information which is somewhere in the header of this discussion, BTW). If things get too bad regarding acceleration, I'll replace wires and go to OEM disty cap/rotor.

  • 0patience0patience Member Posts: 1,712
    in the case of over-gaped plugs, it's not exactly a short, but more as vidtech mentioned, high resistance.
    You are correct, but it was the best analogy I could come up with and most folks understand shorts far better than they understand resistance. :)

    Also, I am assuming that you are sure the miss is ignition related? And that you have checked to make sure there are no codes present? And that the fuel filter has been replaced and you have no vacuum leaks?
    Just some things to think about. ;)
  • irishalchemistirishalchemist Member Posts: 152
    0patience, yeah, you're right. It's a good analogy and would have made it clear to me if I did not know much about cars (which I don't, but you know what I mean).

    As far as other 'non-ignition' stuff, I changed fuel filter (still have busted knuckles to prove it), PCV, and air filter with OEM parts, and 'cleaned' the injectors with techron (although I know there is no real way of cleaning them unless you take them apart and sonicate them...). I also sprayed carb-cleaner around the intake manifold and vacuum lines, and don't see any changes with the idle speed. Finally, I have no codes (I actually made myself the scanner to get the codes the first time I had trouble with the plug wires).

    As I said in the original post, the hesitation is very subtle, and only in damp/hot mornings. I can only tell because on cool/crisp days it's a bit more responsive. If I lived in Florida and I had no cool/crisp mornings, I would not have been able to tell. Also, I think it is related to the wires because that's usually the way wires act up (they are worst in damp weather). Although I know that if I had kept driving with over-gaped plugs I would have beaten the wires to a pulp, I did not know if over-gaped plugs could do a lot of harm to new wires in only 500 miles (1 and 1/2 month...).

    Anyway, my dealer, believe it or not, has the cheapest NGK blue spark plug wires I could find, so I'll get another set and see if that straightens things out.

  • swschradswschrad Member Posts: 2,171
    (high voltage, aka 1500+, and VHV, or 20,000 volts plus) are pretty simple, because I have had to do some things twice in a row. it should be noticed that HV/VHV where it doesn't belong hasn't killed me because I made sure it was not going to break loose when I was done.

    when one parts breaks down in the chain, shotgun 'em all. clean up everything in the path, scrape down the dirt and get to gleaming, re-insulate or add extra insulation where you have evidence of arcing (OK, this applies more to VHV anode circuits in old tube gear), and replace everything in the path that makes sense.

    in the case of color TVs this would include drippy flybacks, the equivalent of ignition coils. in the case of RF power amplifier cages, it can include power RF chokes, usually not the transformers, but generally the VHV wire. always includes peripheral "safety" parts like damper tubes, focus resistors, and formant capacitors in TV. that's new rotor to carheads, and really look at that distributor cap before deciding you don't need to buy one.

    anything that arced over needs to be replaced. anything. all of it. arcs build a carbon track over their length that defeats insulation, and will lead to consistent overcurrent and damaging the VHV generating coils sooner or later. we used to be Very Bad Boys in HS physics, painting conductors between terminals on equipment with colloidial graphite, us merry band of Bruins... carbon tracing is the same stuff, and it's almost as good as silver wire at 40,000 volts.

    if wires are changed, plugs are changed and gaps checked.

    and if one cylinder is misfiring because of deteriorated plug wires, why would you believe the other three, five, or seven are in significantly better shape? the mopar garage in Fargo had a land-office business going in the 60s and 70s replacing one spark plug wire at a time. I didn't have to keep going back once I 'gunned them all with MSW wires.

    not all of my experience has been with cars, but I've been stung before (yes, it's a pun) by doing half the job.
  • desi501desi501 Member Posts: 66
    In 35 years in the business I have never seen an ignition wire fail for a reason other than
    excessive heat
    oil deterioration
    old age
    human destruction

    His statement that it is triggered more from temperature rather than
    moisture could open other possibilities as Intake temp sensors, CTS, mass air flow etc, or even a vacuum leak . Many of these won't set a code. If it did come down to a plug wire, I don't think I'd blame the spark plug.
  • swschradswschrad Member Posts: 2,171
    one problem is that the "wires" aren't wire, but carbon fiber. carbon fiber develops cracks in handing the wires, and as current flows across them jumping the cracks, they erode further. the arcing will also raise temperature in the area and if there is oxygen in the materials of the cable, generate ozone... both beat insulation up. if you can't sink the voltage through the plug, you now have an increased chance that if contamination along the plug wires becomes conductive, you could have the VHV break through the insulation at or near one of the cracks, and once you have deteriorated the sheath with a pinhole, the wire will go downhill rapidly.

    the principle is demonstrated in the wired telephone system every day, where cables subject to lightning strikes or inductive voltages from near-strikes will develop enough voltage to arc through the insulation of the individual wires. you will also, often enough, pinhole the sheath of the cable. this allows water, more deterioration, etc. some of the cable can be and is rehabilitated, some isn't. the problem is most commonly seen in telco land as "bad pairs" that exhibit voltages from Hell due to shorts to ground or to adjacent wires' sources on special circuits, imbalance, shorts, opens, or high attenuation due to multiples of the above between the wires in a communications pair. excessive water in a cable will cause the whole cable to damp out all signals on all pairs. wet cable, once the standing water is drained by piercing the jacket at a low point, is dried using arc welders, one lead on the "tip" and one lead on the "ring" of each pair in the cable. it can take hours or days, and occasionally wrecks the cable.

    it is a well-known fact among cable engineers, from whence I learned it, that PVC deteriorates rapidly when wet, even faster when wet and under voltage, and that voltage and ozone will deteriorate all insulation types at various rates. hypalon rubber, the old standard of ignition wires, was moderately better at water resistance, but heat, cold, and ozone did a number on it. silicone rubber, the new insulation used in primary ignition wires, is much better, but is not endless. teflon is probably more durable electrically and under water, but worse exposed to oil, and it doesn't like to be mechanically shocked at all. nylon overcoat is used in commercial wiring expected to be exposed to oil or heat or motion, like THHN, as environmental protection for the underlying electrical insulation.

    temperature as a deteriorating factor in insulation can be simply explained by one reference. if heat didn't kill plastic or rubber insulation, why are hand irons wired with cords insulated with cal sil or (in the old days) asbestos? or, why are some of the cables in my truck's harness set insulated by paper-coated foil where they run along the back of the engine?

    I got tired years ago of using an ohmmeter clipped to the ends of ignition wires and rolling them in loops to gauge how bad the wire is (10,000 ohms or less, new... over 40,000 ohms, replace.) if it's time for plugs, it's time for wires. and I don't have stumbles any more.
  • desi501desi501 Member Posts: 66
    OK, you went round and round. You mentioned a couple of scenarios that were "human damage" Other than that, the plug didn't ruin that wire! Believe me. It just doesn't happen. The only way a wire that new can be ruined is exposed to extreme heat, oil saturation or mechanic mishandling(which includes punctures). I've seen wires attached to a dead plug for years and just replace the plug ant it fires fine.
  • swschradswschrad Member Posts: 2,171
    most of the chain failures I've seen are in TV and transmitters and so on. if you haven't seen it, and sounds like you're a long-term mechanic, the car VHV system must be built stronger than that. but I sure got tired of gutless plug wires under the Mopar label in the 70s.
  • desi501desi501 Member Posts: 66
    Plug wires still have their share of problems nowadays. The thing that helps now is we have coils putting out 30K volts now so the wire doesn't have to be perfect. An OE set of wires on most vehicles will last about 60-80K except for the 4.6 Fords. They are so long that they're only getting 30-40K. Oil saturation and heat will accelerate the process also but a bad plug doesn't have any effect on them.
  • irishalchemistirishalchemist Member Posts: 152
    Sorry it took so long. I posted in the protege board a week or so ago - The problem is fixed. While I was changing fuel fitler/air filter, I had to wrestle with the air duct from the air box to the throttle body. I decided to re-check everything a couple of weekends ago, and noticed a) the air duct clamp was loose on the air box side right after the MAF, and b) the throttle body was dirty. So, I cleaned the TB, while I was at it cleaned the MAF, and then retightened the air duct clamp firmly. The hessitation is now gone, at least on the butt-o-meter. I know, I may never know what it really was (the loose duct, the dirty MAF, or the dirty throttle body), but I was not about to do one at a time to satisfy my curiosity (I was close to do it that way, but I would be divorced by now if I had taken that route...).

    Cheers, and thanks for all the suggestions,

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