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Ignition
Is the stock setup adequate?
To coin the words of Kevin Cameron, Engine lore is filled with tales of secret ignitions, coils or spark plugs that mysteriously produce extra massive power. But the fact is that a match burns the house down as well as a blowtorch. The power is in the air/fuel mixture, not in the spark. If the mixture is correct and well-mixed, it requires only a minimal spark to ignite it.
As we'll see later on, the stock LET ignition is not too bad, and if maintained properly it can cope with a lot more horsepower before it needs a serious revamp.
Under the punishing underbonnet temps, rubber and electric parts tend to deteriorate quickly. Everything needs to be in tip-top condition if strange faults are to be avoided.
Battery
Everything starts from the battery. If it produces less than 12V (or 13.5V with the engine running) the ignition will never give it's best shot. Most later turbos have a voltmeter, if not it's a good idea to add one. Low voltage is the root of many 'weird' electrical or fuelling problems. Bad earth connections also account for many X-files type of faults.
If the battery is more than 3 years old and it can't hold charge properly, it's better to ditch it for a new one. If it's in a good condition though and just needs a good, slow charging, then an 'intelligent' charger like this "OptimateII" is a good investment:
Coil
It should never be touched with the engine running, the shock could be lethal! The stock coil comes with an 'ignition module' on the side, which is just an overpriced transistor regulating the voltage. Although the official parts guides have a different (i.e. rare, expensive!) part number for it, rumour has it that the XE coil is practically the same. Similar case to the Oxygen sensor.
The battery terminals tend to corrode and need cleaning thoroughly. Perhaps the connector washers and nuts need replacing with new ones, too. It's stupid to let dirt and oxidisation compromise the voltage it receives from the battery.
If the coil is suspected of not delivering the goods (misfires under boost) then a couple of drops of water on the top of the coil will show if there are hairline cracks. With the engine running, look for tiny bubbles. Easy on the water, we don't want to short it out, just see the bubbles. If there are cracks, it's got to go.
Left: stock coil
Right: alternative coil that NOS people use routinely. Unfortunately I didn't find it to be compatible with the engine. Maybe it's the primary resistance that's 1.6Ohms instead of 0.9OOhms, who knows...
At some point I'll come across a coil that fits the LET nicely and will produce a stronger spark.
Beware though, a stronger spark is not necessarily a good thing, as it will demand a pristine path and will try harder to earth itself through the chassis (causing misfires)
Note the lead with optimised shape and length (aircon engine bay). Also note the different plug.
Too many coils, too little time... Here is how to check your coil as well as the poor man's coil tester (local copy here)
Aftermarket Super-Duper Coils
There is a lot of hype regarding 'spark amplifiers', 'hyper 50KV coils' and the like. I've fallen for it myself too in the past - it just sounds reasonable and techno. You know, loads of KiloVolts igniting your pressurised mixture - hey, it can only help, right?
The sad truth is that most are snake oil, much like Slick50, Splitfire plugs and the like. Those that do produce a stronger spark (many don't even achieve that!) have no measurable difference whatsoever, simply because the stock system produced enough spark in the first place. The 'ectstatic' reviews (where they were real) would be from people who had replaced a half-dead ignition system with a brand new aftermarket one - of course it felt better! Mind you, it's not always easy to diagnose a coil that doesn't perform. It may measure right, look right and perform right at most engine speeds, but micro-cracks in the insulation might lead to misfires at full boost. In bad cases just placing a few drops of water on the top of the suspect coil would show this - if they appear to 'boil' then there are cracks hidden.
Modern ignition systems (like the LET for example) are capable of producing more than enough spark energy than that needed for combustion (even at 20psi). If there are misfires, they're probably because of dead leads/plugs/rotor/dizzy/lead routing, or the wrong AFR.
Yes, a wrong AFR can make ignition a nightmare. Either too lean or too rich - it just won't ignite, no matter what the coil output is. It's just NOT COMBUSTIBLE.Changing bits around, like the chip or the oxygen sensor, would probably also change the AFR at those conditions, making it more (or less) combustion-friendly. But because you've also changed the coil (or the leads or whatever) you think it was the coil (or the 'trick' leads) that solved your problem.
This doesn't mean that they are ALL junk: some might indeed be a genuine improvement.
What I would question is the *need* for a (so-called) stronger spark when we're talking about an LET doing 20psi overboost. We're not in 30 or 40psi territory here - now that would definitely ask for some serious ignition improvements!
Distributor
It consists of the main body on the cylinder head, the dizzy cap and the rotor. There are three O-rings in there, change them for new ones if it happens to be disassembled.
These engines eat dizzy caps and rotors for breakfast. They should be treated as consumables, along with spark plugs and the various filters.
These points are less than 5K miles old: (click for larger image)
The dizzy cap is the same as the one from the early 2.0XEs, so it can be found everywhere. The rotor can be a genuine part for peace of mind, but it's cheap anyway.
Be careful, as many motorfactors supply the wrong dizzy cap for the turbo - this is the correct one:
(click for larger image)
Just because a rotor arm fits in the shaft, it doesn't mean it's native.
Both of these arms are sold for the LET, but the thinner one also sits 2mm lower
The (vertical) distance between the centre of a dizzy point and the mating surface is around 21mm
Ideally the distance between the rotor arm tip and the mating surface should also be 21mm.
With some rotor arms this distance can be a few millimetres off. Not good for the quality of the spark, and could potentially lead to misfires. Since everything will be pushed in firmly, there will be no easy way to troubleshoot what's wrong.
Rotor Arm Mod
Also known as the "NOSWizard mod", because it was first described by the NOSWizard. It aims to increase the strength of the spark by 10-20%. It involves scrapping the inline resistor that lives in the rotor arm. (Click for larger images)
Below is a new rotor arm intact. The resistor is within the black bit.
Scratching the resistor reveals a lot of the stuff:
I used a Dremel with an engraving tip, but other tools might do the job:
Below are two rotors - one is stock with the whole resistor, to the right is the modified one. It's filled with solder, effectively short-circuiting the two copper ends.
The stock rotor measures 1KOhm between the two ends. The modified one is practically zero Ohms.
This has to be done with attention to detail because it rotates at half the engine's speed, which is a few thousand rpm. If it's not secure it might disintegrate, leaving you with a weak (or none at all) spark. Also try to use some epoxy resin to cover the lot, in the manner the OEM item does it. Good quality solder has a resin in the core, which floats to the surface once molten - but add more if it doesn't look enough. This will prevent the air within the cap from becoming ionised (used to be a source of inexplicable intermittent faults in older automotive designs). Better safe than sorry.
Be careful to measure the resistance afterwards, and verify that it's zero (or thereabouts). If the copper ends are not electrically connected, then the resistance will be infinite, of course. The car may still run though, as the spark can jump a few millimetres - but it will be weak, and under boost it will misfire.
This is a no-nonsense mod. The car feels stronger and smoother at full boost - no question about it. It also appears to pull cleaner through the whole rev range, an effect similar to advancing the ignition timing by a few degrees. I can only think of two reasons that this could happen:
- Without the resistor the coil now discharges slightly quicker.
- Without the resistor the spark duration is now slightly longer, increasing the chances of finding an ignitable charge specimen within the plug tips.
An inspection of the spark via an oscilloscope would indicate which of the above two is actually happening. Either way, the mod works a treat. Stock turbos may not feel the full benefit, but high-boosted engines will definitely feel happier (apart from the higher cylinder pressures, they also tend to run 'colder' plugs that are less efficient off-boost).
Then why did the manufacturer fit the resistor in the first place? Good question:
One reason is to contain the 'backfire' that occurs after the coil has discharged (a high-voltage spike is sent back into the coil). Having zero-resistance wires is regarded by most people as a 'good thing'. In fact it just shows that they don't understand how these ignition systems work. The manufacturer has added resistors on the path for reliability reasons, these cars are not meant to be rebuilt every 1000 miles!
Another reason is to reduce interference, which is why the recommended spark plugs also have inline resistors ("R" in the name). The stock ignition leads have carbon resistors in there, too (that's why they age and weaken the spark). Getting rid of all these resistors should theoretically make the car fizzle like a mobile phone mast - interfering with the ECU, the radio, the ABS - even the aeroplanes and satellites. In reality it runs just fine - all the people in the NOS forum run their cars like this and they've reported no dental fillings tuning to radio stations.
Please note that the long-term effects of such a modification are not known. There is now extra load on the coil and it might be forced to fail prematurely. Try it at your own risk - just like every other attempt to deviate from the manufacturer's design.
NASA knew of the beneficial effects (in terms of reliability of ignition points) of resistive leads back in 1945!
There is nothing wrong with the OEM leads, quality-wise. But after a few years they will have deteriorated, although this is not always visible. When I comes to replacement leads, my preference is for Magnecores, the 8.5mm red ones. They fit nicely, click everywhere, seal the plugholes, and insulate well.
Leads need to be physically clean, with no carbon deposits or marks at all. Neither should they touch each other or anything metallic. The reason is that sparks find the easiest path to earth themselves, and if they find an alternative route, they'll take it. Misfire or crossfire might result (a lead sparking another cylinder). The stock (plastic) spacers are there for a reason. Use them.
There is a lot of claptrap 'hyperconductivity' theory surrounding trick leads. Read here about Magencore's version of the truth (local copy here)
Tip #1: make sure the leads are securely pushed in, especially on the distributor side. The engine will run fine even if one or two have not fully clicked, as the spark can still jump the small gap (but it weakens). The car however will feel sluggish and that is a fault hard to pinpoint.
Tip #2: if you have an aircon engine, the coil is probably very close to the distributor. This means that the king lead might be far too long. If you cannot source a shorter lead, it's better to coil and secure it with cable-ties (nothing metallic!) so that it doesn't touch anything metallic in the bay, even as the engine rocks wildly under load. The spark can (and will) leak through intercooler pipes, aircon pipes, steel clamps, gearbox cable, whatever. Beware of anything metallic within an inch distance from the leads.
Ideally you'd want a shorter king lead though. Various 'experts' might say that you need a special crimp tool for the Magnecors. Rubbish.
Here is the king lead in pieces
The famous core: wound up spring, nothing exotic
Just cut half of the lead length, and put it back together. The rubber boot will be a bitch to slip back into the outer silicon body.
Don't worry - use some liquid soap, and it will just slot in. After the soap dries, it's good as new
Special crimp tool?
Yeah, right...
Short versus stock lead.
Much better.
Another by-product of the shorter lead is lower electrical resistance. The stock one is 2KOhms, the shortened one a bit less than 1.5KOhms. Every little helps.
Here is more about leads (or 'wires' as americans call them). If it's down, try a local copy
Plugs
The OEM plugs are fine for a stock car. But when the power is raised by 50%, then they are no longer optimal. As a very rough rule-of-thumb, every 50-60 bhp increase should be accompanied by plugs one grade colder. Therefore modified LETs should go for plugs one or two grades colder. Be careful, because not all manufacturers use the same naming conventions for their heat ranges. The 'width' of their ranges can be different, too.
As boost increases, typically the plug gap has to shrink, if misfires are to be avoided. Go too small, and misfires is all you'll get. Ideally the gap should be as wide as possible, just enough to avoid misfires. The stock gap is 0.7mm. An engine running 1 bar would be better around 0.65mm. A high-boost LET at 20psi will probably need 0.6mm.
Iridium and platinum plugs are the best, because they last longer under high-boost conditions. Cheaper ones will also work (if the gap and heat range are correct) but they will need replacing more often. In theory at least.
For a stockish turbo running high boost the NGK BCP-7EV is a good start. It has no extra resistor to weaken the spark (no "R" in the name), it is gold/palladium-tipped for long(er) life (that's the "V") and it's one grade colder than the stock LET items (heat range 7 instead of 6).
The nearest equivalent Iridium is BCPR7 EIX, and can be bought for £36/set from the internet.
Tip: if the car has trouble passing the MoT because of too high HC, and everything else appears fine, then try again with a set of plugs one grade hotter - like BCP - 6EV, or better still, some OEM-replacements.
The instructions recommend that you do not try to adjust the gaps on these, simply verify that they are correct (0.7mm). Banging the ground electrode gently (ish!) on a wooden bench should close the gap if you have to, but pulling it back again can be more tricky as you could exert pressure on the thin (and fragile) tip.
Iridium plugs are claimed to operate more efficiently under high boost and last longer too. Their heat range is claimed to be broader as well. The secret is that the tips are very thin indeed.
My experience - and those of others- however tends to differ a bit.
Robustness is an issue apparently, as Denso iridium plugs have been reported to lose their tips during high-boost operation.
The Denso iridium to the right was lucky and only lost some of the insulator in the centre. Others lose the whole tip.
One wonders where the lost tip ends up eventually. Probably the exhaust valves won't appreciate the encounter, no more than the turbine blades...
The claims about longer life have not materialised in my experience, either. What's worse, I've had them foul (dry) under rich conditions, and they could not 'burn' themselves clean afterwards, resulting in misfires. A new set solved the problem immediately, but left a few question marks on the manufacturers' wild claims about 60K miles service life...
This is an article on iridium plugs from a specialist, trade magazine.
Nothing is substantiated, looks like an infomercial really...
Another similar 'trade' article, both kindly scanned by Chris Hall
Another important aspect is spark plug tip protrusion
The image above shows how I measured protrusion (the gasket thickness is excluded obviously, as it can vary)
ZFR6FIX: quite clearly it protrudes in the combustion chamber 2mm more than the other ones. Hmmm...
BCP7EV
If you feel that this stuff is totally elementary, here is a slightly deeper view of some ignition aspects, explaining detonation, preignition and more
More on NGK's plug naming conventions
Here is a typical page on spark plug diagnosis (local copy here)
Here's another one (local copy here)
Here is yet another one - quite interesting, too (local copy here)
Pseudo-science meets spark plugs with the Fuel Blaster. (local copy here) More ridiculous than Splitfire.
Trivial note: The animation at the top of this page is from How Stuff Works. And either the Yanks have different firing sequence on their 4-cylinder engines, or they don't know exactly how stuff works...
On to Lubrication...
