Do spark plug leads deteriorate over time?

Submitted: Monday, Jul 06, 2009 at 09:50
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I have a '96 80 Series Cruiser on which the leads have never been replaced. Just wondering whether they deteriorate over time and whether they should be replaced.
Thanks from the Moose
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Reply By: Ozboc - Monday, Jul 06, 2009 at 09:57

Monday, Jul 06, 2009 at 09:57
You bet they do ! . also known as HIGH TENSION LEADS - they dop break down over time and cause excessive resistance

as to replacement -- not sure on exact figure - but every few years

Boc
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Reply By: HGMonaro - Monday, Jul 06, 2009 at 09:57

Monday, Jul 06, 2009 at 09:57
they can and do, but in my experience, they work or they don't. Had a Nissan Pulsar that use to need one lead (always the same one) changed on a fairly regular basis (i.e several times in the 240K I had it where the other leads never had issues)

Nige.
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Follow Up By: Member - Peter R (QLD) - Monday, Jul 06, 2009 at 11:00

Monday, Jul 06, 2009 at 11:00
In my old 94 80 series I had a backfire caused by lead arcing and was running on gas at the time.
Major problem with air flow gizmo blowing out and I was 170km from Kununurra with a van on the back.
Was told to change them at least every 80000kms I think it was.

Pedro
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Follow Up By: Member - DOZER- Monday, Jul 06, 2009 at 12:33

Monday, Jul 06, 2009 at 12:33
the hidden cost of gas....whoever installed yours should have put a blow back valve in the line to protect the meter...common for this to happen on these models...
Andrew
b4 you bag me out, walk a mile in my shoes, then your a mile away and have my shoes :)

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Follow Up By: Member - Peter R (QLD) - Monday, Jul 06, 2009 at 13:58

Monday, Jul 06, 2009 at 13:58
Andrew,
It was an Impco LPG system and after the problem someone suggested a sock but the Impco people said their unit was not designed for it.

Not sure if the sock is the same as the valve you mentioned but anyway the vehicle is lno longer mine.

Pedro
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Reply By: tim_c - Monday, Jul 06, 2009 at 12:08

Monday, Jul 06, 2009 at 12:08
Yes, they do. I had to change a set on my Jackaroo because they were arcing when the engine was under load (ie. I wouldn't get enough sparks in the right places at the times when I most needed them!). And it certainly pays to shop around!

If you have a multimeter, you can check the resistance of them to see if they actually need replacing (rather than just replacing at regular intervals). Unfortunately I can't remember what the resistance actually should be but perhaps someone else, or a google search, might be able to inform you?

BTW: If you buy from AutObarn, you'll have to specify that you want them for a Landcruiser with a PETROL engine! :)
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Follow Up By: Member - joc45 (WA) - Monday, Jul 06, 2009 at 12:40

Monday, Jul 06, 2009 at 12:40
Hi Tim,
perhaps I've missed something, but why do Autobahn need to know if it's a petrol engine?
There are not a great deal of diesel engines which need spark plug leads :D
cheers,
(puzzled) Gerry
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Follow Up By: tim_c - Monday, Jul 06, 2009 at 13:05

Monday, Jul 06, 2009 at 13:05
I was shopping around for a set and the staff member at AutObarn was flicking through his book looking for a part number and he asked "petrol or diesel?". More out of habit than anything else, I answered "petrol" (it's the same question I always get when buying bits) then I realised and wished I'd said "diesel" just to hear him say something like "we don't stock them".

A funny look came over his face afterwards as if to say "I'm so glad this dumb customer didn't tweak to it otherwise I'd have looked like a real goose!" Seriously, I think he asked the question out of habit as much as I answered it, but was thankful I didn't say anything! :)
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Follow Up By: Louie the fly (SA) - Monday, Jul 06, 2009 at 17:19

Monday, Jul 06, 2009 at 17:19
I've never had to replace them on a diesel. They seem to last forever.

Louie

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Follow Up By: tim_c - Monday, Jul 06, 2009 at 17:49

Monday, Jul 06, 2009 at 17:49
It's just as well Louie, because I've yet to find a parts retailer that stocks them :)

A bit like the water pump for my Dad's ol' VW...
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Follow Up By: Member - joc45 (WA) - Monday, Jul 06, 2009 at 22:34

Monday, Jul 06, 2009 at 22:34
Interestingly, I did come across diesels with spark plugs back in the early 80's. Well, they were classified as diesels. These were stationary engines used on gas pipeline valve sites, running off CNG, and they (mysteriously) used spark plugs. Dunno how they were classified as diesel if they needed plugs. They certainly sounded like a diesel when running. The primary power source was from Ormat closed-loop gas turbines, with these "diesels" used as a backup or when more than 2kw of power was needed for maintenance work.
Anyway, I doubt if the operators would have called in Autobahn to work on these babies!
Gerry
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Reply By: krawczuk - Monday, Jul 06, 2009 at 12:19

Monday, Jul 06, 2009 at 12:19
hi, also the plugs deteriorate as well , the electrode goes high resistance , and the spark can track along the center ceramic insulator.
mark k
AnswerID: 373300

Reply By: Member - DOZER- Monday, Jul 06, 2009 at 12:30

Monday, Jul 06, 2009 at 12:30
Heat deteriates them, if you run gas,they deteriate quicker due to more heat....bottom line is you can check them, make sure if anyone has been in there that none of them are rubbing on the lloy tappet cover, check resistance of them and compare with spec....but if it is going ok, leave it....you will notice a miss when you put the right foot down if they are sus...U r looking at 200 bux for a set aftermarket and 350 toyota roughly....
Andrew
b4 you bag me out, walk a mile in my shoes, then your a mile away and have my shoes :)

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Reply By: blown4by - Monday, Jul 06, 2009 at 13:08

Monday, Jul 06, 2009 at 13:08
Yes they do break down due to heat, physical damage, ozone and just old age. They can suffer an increase in resistance and the insulation properties deteriorate with age as well. Repco sell a Champion brand of after-market steel core hi-insulation LPG lead set specifically for LPG installations which I personally have found to be very good leads. Also check the dizzy cap where the leads plug in, including the coil lead, for corrosion and any burning caused by high voltage tracking. On re-assembly use silicon grease. Keeps the moisture out and prevents corrosion. Also check the cap internally for burning around the contacts & if the cap material is good just clean the contacts lightly with emery tape. Check the rotor button to make sure it is free to move in the cap and check the rotor for deterioration & clean the end contact if necessary. If I was going to the expense of new leads I would recommend a new cap, new rotor, new plugs, etc. After-market good brands such as Bosch are not all that expensive. Also note that with LPG any electrical will be magnified when compared to running on petrol. Before you do replace anything lift the bonnet on a pitch black night while the engine is running and look for any sparks. The corona glow around the spark plug ceramic insulators is nothing to be concerned about but any visible or audible hi-tension sparks is.
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Reply By: Member - ross m (WA) - Monday, Jul 06, 2009 at 15:41

Monday, Jul 06, 2009 at 15:41
I always remember the time I took my FJ73 for a tune up the 1st time I got it.

When I went to pick it up the old mechanic waved the old leads around and said "it still on its bloody original leads after 20 years and 200000klm"LOL
AnswerID: 373317

Reply By: Member - Malcolm (Townsville) - Monday, Jul 06, 2009 at 17:16

Monday, Jul 06, 2009 at 17:16
In '82 I used to use an Allan Smartscope for diagnostics. Could pinpoint the exact lead or plug that was faulty. Replace one item and everything was again smooth as.

Workshop down the road used to say they were wasting $45 for the diagnostics tests. "We do tuneups for $25 plus parts!!". Sure they did. New set of HT leads and 4/6/8 plugs. Cost certainly was greater than diagnostics with one lead or plug AND they most probably threw away some perfectly good parts.

Fact is nowadays nearly everthing is done by computer diagnostics because the "mechanics" don't know anything else.

Malcolm
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