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Bad plug wire effects?

 
Old 01-10-2019, 07:51 PM
  #1  
merchauser
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Default Bad plug wire effects?

My plug wires (probably original) are arcing and leaking horribly. (call you tomorrow, roger)

what symptoms should I be having? car idles rock steady, and I don't notice any missing?
what specific issues do leaking plug wire exhibit? hard starts, bad idle, poor performance,
odor at exhaust, hesitation? lean or rich condition? generic searches have given generic answers.
(would love to hear that new wires will give me 300 more HP...…………….lol)
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Old 01-10-2019, 10:20 PM
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Chuck Schreiber
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All the above...
If really bad, you can turn out the lights in your garage and see if there’s any “lightning/gremlins” going on.
Sounds like the car is running good.

The experts (Doc B, Sean, Stan, David, Stretch) will chime in. They know better than I.

I put new wires, coils, dist caps, plugs, one day on the GTS under Sean’s tootalige (spelling?) didn’t do a $##T bit of good.
But It ‘felt good’ doing it and knowing it was good to go for another 20 yrs.
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Old 01-11-2019, 07:34 AM
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merchauser
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^^^^^^thanks chuck. I have the fireflies, lightening gremlins, and/or dancing fairies in spades! wires are leaking like crazy.
still want to know what exact symptoms do plug wires present, can the issue(s) be intermittent, and is there a gray area, where
wires are a problem, but the wire is not 100% bad, or 100% good (all or nothing)
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Old 01-11-2019, 09:47 AM
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Ignition leads are good for about 15 years or so and after that it is a bit of crap shoot as to what happens. I suspect the leads from the coil to the distributor are a tad more vulnerable to degradation and of course each one of those feeds four cylinders. Once the insulation breaks down then needless to say spark energy is being lost and the impact will vary from slight to significant. What might also happen is that the impact of the degradation may vary with relative humidity in the atmosphere- the more moisture the thing has to deal with the more electrical leakage will take place and at some point a misfire may well happen
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Old 01-11-2019, 10:01 AM
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merchauser
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can't understand why car idles so steady and smooth since 6 of the 8 wires are leaking excessively.

assuming that poor spark will cause rich condition? fuel not fully burned? I don't have that noticeable rich smell from the exhaust:
is that because the O2 is seeing rich and leaning everything out??
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Old 01-11-2019, 10:01 AM
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Chuck Schreiber
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Originally Posted by merchauser View Post
^^^^^^thanks chuck. I have the fireflies, lightening gremlins, and/or dancing fairies in spades! wires are leaking like crazy.
still want to know what exact symptoms do plug wires present, can the issue(s) be intermittent, and is there a gray area, where
wires are a problem, but the wire is not 100% bad, or 100% good (all or nothing)
Sounds like you are on the right track. Intermittent, fireflies, running issues, etc..
Start w the wires, but you’ll probably end up doing the rotors, caps, etc.
Everything that Fred says above as well.

Forgot to ask, do you know how long it’s been since all that has been changed?
If it’s original, you’re long overdue.
I’m a bit of a fanatic. I’d do coils, wires, plugs, rotors, caps, and I think there’s some ground wires there as well.

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Old 01-11-2019, 10:15 AM
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merchauser
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^^^^^chuck, the caps and rotors were done 8k ago. thinking they are OK? the wires appear to be original, and there are no receipts to show coils were ever replaced, as well.
was not expecting you to report that new ignition parts did nothing for you??

fred, will bad wires cause unburned fuel, which means rich? and then in turn, computer compensations result in lean condition? I bet you know where I am going with this? lol
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Old 01-11-2019, 10:26 AM
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I'd at least replace the wires then. Sound like the rotors and caps are good at 8k old.
if you're seeing fireflies, you're more than likely going to get intermittent or prolonged running issues.

To Answer your other question. When I had my GTS, I was replacing anything that was in question. I had NO records of any of my ignition parts being replaced. They looked good, no fireflies, but it was a while I was in there. So I really didn't think it was going to change the way the car ran, as it ran pretty good to begin with. No issues like you are having currently.
The next project after that was to do the top end refresh. When Sean did that, we replaced EVERYTHING whether it looked like it needed it or not. Sorry, I'm just **** that way.

I'd just replace the plug wires first, not overthink it, and see how it runs. Plugs are a cheap While you're in there as well.
If the wires don't cure your running issues, at least you know it's done (and needed to be done) and at least you eliminate that from the list.

Good luck w the project! The wires are relatively easy, just take your time.
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Old 01-11-2019, 10:35 AM
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merchauser
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^^^^^wires will be ordered today; what I haven't mentioned, is that I have been experiencing intermittent power changes. there seem to be 2 COMPLETELY different driving modes:
1) good power, and 2) amazing power. mode 2 was found by pulling the RH wires up and away from the engine and installing a few wood strips to keep them away from the block.
I am hoping that new wires will keep me in mode 2, and that mode 1 is a result of those bad wires arcing against the block; but I don't want to suffer magical thinking. lol
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Old 01-11-2019, 12:32 PM
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Originally Posted by merchauser View Post

fred, will bad wires cause unburned fuel, which means rich? and then in turn, computer compensations result in lean condition? I bet you know where I am going with this? lol
I suspect that once the system starts leaking electricity it will be a bit like a pipeline with a hole in it -more flow requires more pressure and thus more leakage so the attrition at idle may well be negligible but as the demand increases the leakage will likely increase and be more problematical. I know that when a coil is failing idle and mid range may be ok but at some point the thing will not rev no matter what- whether a similar characteristic can happen remains to be seen. I suspect my earlier theory about relative humidity will be more pertinent in terms of the phenomena you describe wherein there seems to be two modes of operation.

For the closed loop system you operate under, if there is a misfire and fuel flows through unburnt the NBO2 may sense this and tend to lean things off proportionately- again whether that can happen to any noticeable extent remains to be seen albeit there is a limit to the correction the NBO2 can cause to happen.

Bottom line- most engines do not respond well to leaning off the mix beyond about AFR15.5 and the 928 is no exception
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Old 01-11-2019, 01:02 PM
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Bad wires will sometimes run OK at idle because they're not being stressed electrically (frequency of pulses) and they're usually not vibrating around like they do when underway. One of the best test for electrical wires is a spray bottle full of wather that creates a fine mist. When the car is running, you mist around the wires and listed for runnability changes caused by the introduction of the water getting through the isolating insulation. If there's any change in sound, replace the wires. Can do the same test jiggling them too looking for weak spots or breaks in the wires themselves. Another symptom of bad wires is the car stumbling badly under hard acceleration and / or higher rpms where the wires can't efficiently carry the electricity and that causes the plug not to fire, creating a stumble, bog, or dead spot or spots. Be careful how long you diagnose this as you're pumping fuel into cylinders that may or may not be firing, which washes the oil lubrication from the cylinder walls.
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Old 01-11-2019, 01:22 PM
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Poor ignition events will lead to lower fuel economy as the flame front at ignition doesn't fully burn the mixture in the cyl. Reduced power also. Ideally, as the mixture ignites, the flame front progresses from the spark plug across the combustion chamber, and all of the fuel is consumed with the Oxy in the chamber. In a full burn cycle, very little unburnt fuel is left over to exhaust. As the spark weakens, the flame front slows, and doesn't fully burn the entire mixture before being exhausted on the next stroke. The O2 sensor will compensate for this by reducing the pulse width of the injector, which also lowers the power output. But, there is a limit to what the O2 sensor can compensate for within the FI maps coded into the LH. As the spark gets weaker, more unburnt fuel is exhausted into the air, and you may smell a sweet odor at the tailpipe. Noticeable lack of power, as well as the increased fuel used.
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Old 01-11-2019, 01:48 PM
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merchauser
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^^^^^^so if more fuel is not correctly burned, then that would create a rich condition? and then sensors would tell management to lean things
out? is that correct? and in turn would that pull back timing adding another performance issue?
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Old 01-11-2019, 01:56 PM
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I can't say that the timing will be affected, but surely the LH injector pulse will try to be reduced to work toward a leaner condition. Retarding spark would not be indicated, but someone with greater knowledge of the EZK functions might be able to answer. Generally speaking(not 928 specific), timing retard is only needed when one has a detonation event, or pre-ignition due to poor fuel quality, overheating, burning ember in the chamber, over lean condition. If it were me - I would not retard timing for over-rich mixture, but again - this is dependent on the guy who wrote the EZK code, and how it interprets the output of the O2 signal.
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Old 01-11-2019, 01:59 PM
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The ONLY reason why 928 plug wires do not get changed very often is the EXPENSE !!!! And having leakey wires becomes a disaster when a fuel line lets go.....
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