Practical Automotive Maintenance: Ignition

Back to course

Watch This Course

$99 USD

-OR-

Or 8 easy payments of only $12.38 USD Instant access. Easy checkout. No fees. Learn more

Enroll Now
8 easy payments of only $12.38 USD

Course Access for Life

60 day money back guarantee

Ignition

10.22

00:00	In this section of the course we're going to cover some of the miscellaneous service items and consumables that are regularly replaced or inspected with performance focused servicing and maintenance.
00:10	Let's start with the basic consumables found in ignition systems.
00:14	But first we need to understand how the system functions.
00:18	The ignition system is responsible for igniting the air fuel mixture inside the engine cylinders to create the combustion necessary for engine operation.
00:26	Understandably, the quality of this combustion process relies on the ignition system components being in good working order.
00:33	Over the years, ignition systems have evolved from complex mechanical designs to sophisticated electronic setups.
00:39	But the objective remains the same, to provide a controlled spark that initiates combustion in each cylinder at the correct time.
00:47	In older ignition systems, a mechanical distributor was incorporated to direct the high voltage electrical energy to the correct cylinder.
00:54	The distributor contains a spinning rotor arm which turns at half engine speed.
00:59	Hence, it's correctly timed to a full engine cycle which takes two full engine revolutions or 720 degrees of crankshaft rotation.
01:09	The rotor directs the electrical energy to the appropriate spark plug wire which is also called an ignition lead, sending it to the correct cylinder at the right time.
01:17	This is achieved via a distributor cap which has a post for each cylinder which aligns with the spinning rotor arm.
01:25	The electrical energy travels down the wire to the spark plug where it jumps the gap between the centre and ground electrodes, creating a spark that ignites the compressed air and fuel mixture.
01:35	This explosion pushes the piston down, generating the torque that propels the vehicle.
01:39	Modern ignition systems usually ditch the distributor in favour of individual ignition coils.
01:44	These can be incorporated in a range of different ways and we'll start with wasted spark coils.
01:50	This is where a single coil provides spark to two cylinders simultaneously, one on the power stroke and the other on the exhaust stroke of the opposing cylinder.
01:59	The spark that occurs on the exhaust stroke has nothing to combust, so it doesn't do anything, hence the name wasted spark.
02:05	Next we have coil near plug where each cylinder has its own coil and a short ignition lead connects the coil to the spark plug.
02:12	Lastly there's coil on plug where every cylinder has a coil that fits directly onto the spark plug, eliminating the need for an ignition lead.
02:21	Regardless of the specifics of the ignition system layout, modern fuel injected engines utilise a range of sensors to calculate load and engine speed, so the spark can be triggered at precisely the right point.
02:33	Let's next talk about some ignition system components that are considered consumables, meaning they wear out and require periodic replacement for optimal performance.
02:41	First spark plugs which are the most frequently replaced ignition system component.
02:47	Spark plugs wear out due to the constant arcing and high temperatures they endure, potentially leading to fouling, electrode erosion or carbon build up.
02:56	Worn spark plugs can cause misfires, poor fuel economy and hard starting.
03:00	Under normal driving conditions most copper plugs will last 30-50, 000km whereas platinum or iridium plugs generally get anywhere from 100 -160, 000km.
03:13	The reality is though as enthusiasts we're often not driving these cars under what's considered normal conditions.
03:19	So, plug changes tend to be more frequent in high performance vehicles that are driven hard on the street or the racetrack.
03:25	Thankfully, in most cases at least, spark plugs are easy to remove and replace, requiring a simple removal of the lead or coil.
03:33	It's then just a case of using a spark plug specific socket and an extension on a ratchet to unwire and remove the plug.
03:40	So, exactly what should we be looking for once the plugs are out? Plug reading is part science, part art and would require an entire course of its own to do justice to.
03:50	That being said, most people who use the term plug reading are trying to infer tuning related information from the spark plug condition.
03:58	And that goes beyond the scope and purpose of this course.
04:01	Instead, we're solely interested in the physical condition of the plug and whether or not it's still able to perform its job adequately or is in need of replacement.
04:10	So, let's start with an overview of the plug itself.
04:12	A used spark plug that's in good working condition should present with a light tan, brown or grey colour to the ceramic insulator in the centre of the plug, as well as the ground strap.
04:23	The specifics of the colouring will depend on the fuel used as well as any additives.
04:28	Thick black carbon or oily deposits on these parts are a red flag that something is either mechanically wrong with the engine or there's a tuning issue.
04:35	The electrode and the ground strap should be clean with sharp edges and no sign of erosion or rounding.
04:41	It's also worth checking the ceramic insulator for any sign of cracking.
04:45	If this cracks it can fall out and create a lot of damage inside our engine.
04:50	If there's visible erosion to the electrode and ground strap or in extreme cases if the ground strap is missing partly or entirely, this is also an indication that there's an issue with our tuning.
05:01	Problems like this are important to note since just replacing the spark plugs with a new set will likely end up with the same situation a few hundred or a few thousand kilometres down the road.
05:11	Looking at the plug externally, the white porcelain insulator section can crack, often due to over tightening when being installed.
05:18	In which case the plug is unusable and must be replaced immediately.
05:22	We should also take a good look at the condition of the threads on the body of the plug as it's not all that difficult to do damage by cross threading during installation.
05:31	Lastly it's important to understand that even if it appears that only one plug has an issue, it's always best to replace them all at the same time.
05:39	Let's move on to the spark plug wires, also known as ignition leads.
05:43	As we touched on earlier, in traditional non coil on plug systems, these carry high voltage from the coil or distributor to the spark plugs.
05:51	Over time the thick insulation material can degrade, leading to potential misfires or poor engine performance.
05:57	Essentially the same problems we might encounter with a damaged spark plug.
06:01	Visually we can carefully inspect the wires, checking for cracks, splits or brittle insulation.
06:06	Burn marks or melted spots from arcing or touching a hot part of the engine are another big red flag.
06:12	If nothing obvious shows itself during a visual inspection and the problem is bad enough to result in one cylinder not firing at idle, we can unplug one lead at a time, listening for the variation in engine behaviour or sound.
06:25	If we unplug a lead and nothing changes, we've found the problem lead.
06:29	This is what's known as a cylinder drop test.
06:32	Just ensure if you're performing this test that you only touch the lead and not any other part of the engine or car, as you could inadvertently end up giving yourself a nasty shock.
06:42	We'll also be able to find a specification for the resistance of our spark plug leads, either in the workshop manual for stock leads or from the manufacturer for any aftermarket leads.
06:52	This spec can then be checked with a basic digital voltmeter with the lead removed.
06:56	A word of caution here though, I've personally not found this to be a 100% conclusive test.
07:01	And if we're messing around with our cars often enough, it's usually advisable to keep a handful of spare ignition leads that we can swap in to test a potential dud instead.
07:12	If our car is more modern and uses a coil on plug system, we'll generally be able to get more life out of these components than we would with the leads.
07:20	And they'll often last the life of the vehicle.
07:22	However, they're not indestructible, especially if they're seeing any type of harsh environment.
07:27	If they do fail, we'll usually be looking at the same symptoms as we'd find with a lead failure, rough running or a misfire under load.
07:34	As it's going to be a more modern car, we may also get a MIL or MIL light on the dash and a scan tool plugged into the OBD2 port will generally be able to tell us exactly which coil is the problem.
07:46	If this is the case, it's always a good idea to pull out that coil and swap it into a different cylinder and check that the code has moved with it.
07:53	This just allows us to be sure that it's a coil that's the problem and not something else before we go out and spend money replacing it.
07:59	Failing that, we can also perform the same test as before, removing one coil at a time while the car is running and listening for a change in engine behaviour.
08:08	Again, if there's no change, the coil is well and truly dead.
08:11	Coils are replaced, not repaired, though they're usually not astronomically expensive unless we're dealing with something special.
08:18	One point worth considering with any ignition system problem is that these are most likely to become an issue when the engine is under high load, particularly if it's an engine with forced induction.
08:29	The reason is that as we increase the mass of fuel and air being crammed into the cylinder, it becomes harder to ignite the fuel air charge and this requires more spark energy.
08:39	So, be mindful that some of the ignition system problems that we've just covered may only make themselves noticeable at wide open throttle and high RPM.
08:47	Some stock coils are absolutely adequate for this task in stock form, but with insufficient additional headroom to reliably create spark once an engine is modified with additional boost.
08:58	An example of this is the stock wasted spark coils fitted to the Mitsubishi CD5A GSR Lancer.
09:05	This was the little brother to the Evo and powered by a turbocharged 1.8 litre 4G93 engine.
09:11	Despite the coil packs on face value appearing to be the same as the 2 litre 4G63, the 4G93 coil packs would consistently suffer from misfire once boost was increased.
09:23	Fortunately, the workaround in this case was to simply switch to the Evo coil pack which was a plug and play upgrade.
09:30	Let's summarise what we've learnt about ignition system maintenance.
09:33	Key consumables in an ignition system include spark plugs which wear from heat and arcing and are normally replaced at intervals of 30-50 , 000km for copper and 100-160, 000km for platinum or iridium.
09:48	But this becomes irrelevant if the vehicle is used for high performance driving on the street or the racetrack.
09:54	Worn or damaged plugs cause misfires, poor economy and rough running and should be inspected for electrode wear, cracks, thread damage and ceiling washer leaks with all plugs being replaced together.
10:06	Traditional ignition leads can also fail from cracked insulation or burns while coil and plug systems last longer, but show similar symptoms when faulty, typically diagnosed with scans or cylinder drop tests.