Yet another Spark Plug thread.

[Nick Mann]

My knowledge of spark plugs is currently rapidly increasing. This is because I had a very disappointing rolling road run yesteday, recording 174.3 BHP and 287.3 lb/ft torque.

The operator came out to me and instantly asked when the last time I change the plugs was. He said that the plugs were breaking down under load and I was easily losing 50 bhp by 6500 rpm.

I have ordered the NGK Iridiums mentioned all over these forums, in the 7 heat range rather than the 6, (BKR7EIX) so I shall fit these as soon as they arrive. I have removed the plugs from the car and discovered that they are PFR6G11's. Can anyone enlighten me as to what these are? The standard platinums are PFR6J11 but what difference does the G make? I have cleaned them up, checked the gap and re-fitted them until the new ones arrive.

Also, do people think that these spark plugs could be the reason I am losing so much power?

[Kieran]

I don't think the G makes much difference. In fact, the NGK cross reference lists the BKR6EIX as a match for both.

I think the more significant part is the '11'. This indicates 1.1mm plugs - that's too big a gap and on a boosted car like yours, I wouldn't be surprised if it's blowing the spark out.

[Nick Mann]

The gaps had all been set much smaller - at around 0.6-0.7mm. Except one which was more like 1.0mm. I have re-gapped tham all to 0.75. They all had a brown halo at the bottom of the white glass insulator, where the part number is printed. Does that mean anything? The halo cleaned off with elbow grease.

[swinks]

Smokey-brown traces may indicate faulty HT leads/ignition coils.

[Nice But]

I had a set of NGK's on my supra thet leaked compression when I wound the boost up......... swore never to use them again. Guess what I've got in all my cars...... that'll be NGK's then.

Could be as Swinks says though a bit of tracking......... 50hp is a shed load to lose, it seemed bloody quick to me /rally

[Davezj]

so the gap on a vr4 should be about 0.8mm, that's interesting. as i think mine are gapped bigger than that, at about 1mm. maybe i should reduce the gap. it will also give me a reason to take the inlet manifold off, and inlet pipeing so i can do some messing about with boost gauges.

[White Lightning]

Blimey, that's a bit down Nick ... :speechles

At least the torque is good ... so that would suggest a problem in the high rev range. I guess that's why the guy suggested plugs. It certainly sounds like a good starting point anyway.

[Nick Mann]

Sorry - should have said that the BHP quoted was ATW. I have had MUCH higher torque and a good 50 bhp more in the past, so the guys idea of plugs is certainly the first place to look.

Kieran - have you still got a selection of leads lying around anywhere? :P

[Nick Mann]

Smokey-brown traces may indicate faulty HT leads/ignition coils.

There is a coil pack for a pair of cylinders. As all 6 plugs had the same brown ring at the base of the insulator, I guess the coil pack theory is not so likely. But leads could be an idea. They look original, and certainly have no markings on them to indicate that they are not. Do leads ever break down? I assume they do, but at what point? My car has 150,000 on the clock now, so if they are original, they have carried a fair amount of power now!

[Kieran]

I'd say the brown is just plug corona. Have a look here:

http://ngkntk.in/english/techinfo/qa/q17/index.html

And yes Nick, if you need them I have a choice of two Sets of plug leads here!:scholar:

[Nick Mann]

Yep - that looks like it! So hopefully just a sign that the plugs are old.....

Kieran - I hope that my leads are fine, but I'd rather not buy a set to discover they mde naff all difference. If I'm still having issues when we meet next month, I'll ask if I can borrow a set for a while. :iloveyou:

[Kieran]

No problems. :scholar:

[swinks]

There is a coil pack for a pair of cylinders. As all 6 plugs had the same brown ring at the base of the insulator, I guess the coil pack theory is not so likely. But leads could be an idea. They look original, and certainly have no markings on them to indicate that they are not. Do leads ever break down? I assume they do, but at what point? My car has 150,000 on the clock now, so if they are original, they have carried a fair amount of power now!

Brilliant.../pan You should do it at 100k miles at least. Yes, HT-leads use to wear as the result of ageing (i.e. resulting in misfiring, lack of ignition, overheating plugs). How can you expect any heavy performance using old leads...?

[Nick Mann]

It doesn't seem obvious to me? The lead is a conductor? Do you change your earth strap or starter motor cables every 100,000 miles?

I don't mean to sound irritable!

Any explanation of why the leads break down? I can see that improved leads can give improved performance, the same as with any electrical improvement, but I can't see why age kills a conductor. Does the high voltage break down the insulation or something?

[Davezj]

It doesn't seem obvious to me? The lead is a conductor? Do you change your earth strap or starter motor cables every 100,000 miles?

I don't mean to sound irritable!

Any explanation of why the leads break down? I can see that improved leads can give improved performance, the same as with any electrical improvement, but I can't see why age kills a conductor. Does the high voltage break down the insulation or something?

I would imagine so, think of the HT lead as a pressure pipe with high pressure fluid running through it, it will fatigue at some point and split. the HT lead has 20-30 thousand volts (very low current) running throuh them so eventually this contained high voltage will break through the insulator (pipe).

There is a way of easily test your HT lead breaking down, but it is pianfull. just grab the lead when the car is running. if it is breaking down you get a shock. A bit extream but it is a good detection method.

or you could get a good earthed cable and run it along the HT lead if you see a spark it is breaking down.

Often HT lead break down where they are clipped in place due to the continuous vibration and rubbing. you can also use a piece of bent wire in the end of the ht Lead and hold it to the engine block (good Earth). and look to see how strong the spark is, and compare it with the rest of the HT leads.

Just some thoughts.

[bradc]

I'm in the same mind set as Nick, I don't see how HT leads break down, I've always thought it was just BS perpetrated by guys who want you to spend money (and lots of it) on stupid cables

[Kenneth]

I'm in the same mind set as Nick, I don't see how HT leads break down, I've always thought it was just BS perpetrated by guys who want you to spend money (and lots of it) on stupid cables

From what I understand the shielding, or the ability for the sheath to resist conducting degenerates and can lead to leakage. If bad enough you can see the cable arching to the cylinder head.

[bradc]

I'd pay to see a video of that :)

/searches youtube

[Eurospec]

The leads do break down, and when they do you will start to see them sparking across amongst themselves, or between lead and block/head/whatever bit of metal is there.

As to why they do it, i dont know, but i assume its because the insulator coating starts to get stiff and brittle from all the heat cycles and eventually they split, leaving the conductor free. In extreme cases, the conducter will also start to break too.

Moisture obviously doesnt help.

If your rolling road has an afr trace on it, you will see the missfire as a lean spot on the fuel curve, and you will feel the car spitting as you drive.

Hope that helps,

Cheers,

Ben.

[Nick Mann]

If your rolling road has an afr trace on it, you will see the missfire as a lean spot on the fuel curve, and you will feel the car spitting as you drive.

Now that is interesting info. I haven't got a print out of AFR. I have ordered new plugs, so I was intending to go back to the same place and recheck with them in. I'll get them to log the AFRs as well then.

Thanks for all the info on leads deteriorating too. I'm still unconvinced about losing conductance, but I can wrap my head around losing insulation. I'll try the shorting the lead out routine when I get a chance, to see if the insulation has broken down. If I get no sparking, then I might consider grabbing the lead! But to be fair, I'd want to do that test on a good car too. In the meantime I will see if I can find out anything more.

[swinks]

Yeah..., guys. HT-leads - the wire with running few kVolts. Nobody is bothered. The insulation got ageing so within several years (usually 10) or mileage (after 100k check) 'cos of moist, engine hot, shakings etc. It's only a rubber/silicone. So I'd suggest to check and eventually replacement. Cracks on insulation are not visible, 'cos of hi-voltage surface outflow of course, so problems with sparks, fuel burning itc.
My simple way of checking is (not painfull):
1. wait till darkness
2. open bonnet, remove engine cover
3. run engine
4. from 15 cm distance spray water fog all over leads (i mean real fog, not making leads just wet)
5. if could see shinning leads like x-mas tree - you leads rubbish
6. if still darkness below bonnet - OK

And... it's NOT an expensive stuff. In Poland it's replaced every 150k km in service.

[White Lightning]

I'm still unconvinced about losing conductance, but I can wrap my head around losing insulation.

I think the two things go hand in hand don't they? If the insulation has broken down somewhat then some of the electricity that should be going to said spark plug will be "leaking" elsewhere. And thus not giving you as good a spark as it should ...

[Nick Mann]

They are not quite the same.

Conductance is a measure of a materials ability to carry current, and is dependant on the materials resistance and the amount of it. For the conductance to change, the resistance of the conductor must change, or the cross sectional area.

Insulation is something that has very low conductance, or very high resistance.

The performance of the HT lead will be dependant on both, for sure.

Swinks - I like the fog misting idea. It sounds better for my health than seeing if I can conduct several thousand volts through my fingers!!

[White Lightning]

Okay, maybe I didn't articulate myself very well ... /pan

I understand the difference conductance and insulation (I work in a hardware engineering team so I should do ... :uhoh: ) but what I mean is that even if the conductance has remained the same, the fact that the insulation may have broken down somewhat will mean that some of the juice that should be going to the plug is now going elsewhere ... and thus giving you a weaker spark.

[Nick Mann]

Yeah - potentially!

You could be losing power through broken down insulation. No argument. In the post where I proposed that as a question, that was the only way I could see the leads deteriorating. I had just never heard of HT leads dieing without physical damage or corrosion of the contacts at one end. So I was sounding a bit confused!

[Eurospec]

We always have the 'nope, i'm not grabbing them, you do it' discussion here when it comes to a suspect lead. Once you get a good belt off them, it does make you think twice!

Cheers,

Ben.

[Nutter_John]

done it on my first car , engine was running never crossed my mind how much volatge was being push through the lead , until i shout fecking hell very loud having just grabed a lead to move it out of the way .

Never again

[Paul Beazer]

Yep, you do it once, you wont do it again!

[Nice But]

I suppose not just the breakdown of the insulation being a factor also the actual connections at either ends may degrade over time.

I remember I had a lead problem on my V8 rover some years ago - expensive silicone leads - one lead went intermittant at high temps..... never happened in the winter only when it was warm...... eventually found it after pharting around for several months...... So I spose they are the same as everything, they have an ultimate shelf life....

[Turbo_Steve]

It's only a little jolt, ya girls! It doesn't even sting, (well apart from your fingertips) it just makes your arm go all floaty.

Something with a little more current and even higher voltage...that leaves you seeing stars, a massively achy neck and spine and achy teeth / jaw.

Please note, I wouldn't advise anyone gets an electric shock. Especially accross your heart which is likely to kill you.

[Davezj]

i seem to remeber the service schedule in a workshop manual that had the HT leads as service it of 2 years 24k miles. but this was about 15 years ago and i imagine the ht leads produced today are better than 15 year old designs.
But look at my HT leads on my car they look original and the car is a 1996 which is 11ish years old anyway.
There is somthing else to consider as well, only the 3 back cyliders actually have HT leads, the front 3 are directly connected to the coil packs.
The original leads on my car are very thin and look quite weedy only about 3-4mm across not like the 8-10mm leads i used to get for old Mk2 Escort.

[Kieran]

I got 'belted' by a leaky kettle when I was younger. It's a weird feeling. It felt like my arm had suddenly gone magnetic, I flicked my arm (or my arm WAS flicked, i'm not sure which!) away, staggered backwards into the opposite worktop and then noticed that my legs had gone all feeble!:inquisiti

Could have been a lot worse I guess but certainly not an experience I would recommend, nor one I wish to repeat!!:speechles

[miller]

I got 'belted' by a leaky kettle when I was younger. It's a weird feeling. It felt like my arm had suddenly gone magnetic, I flicked my arm (or my arm WAS flicked, i'm not sure which!) away, staggered backwards into the opposite worktop and then noticed that my legs had gone all feeble!:inquisiti

Could have been a lot worse I guess but certainly not an experience I would recommend, nor one I wish to repeat!!:speechles

you were lucky there wasnt a garage door behind you/pan


Its my next job the leads. You wouldnt believe the world of difference it made replacing them on my old GTO. it idled like a dream, just an all round sensible replacement. Due to the age of the cars i suppose you could call it an upgrade.

Camskill do them right?


Mike