Ignition timing, in a spark ignition internal combustion engine, is the process of setting the time that a spark will occur in the combustion chamber (during the compression stroke) relative to piston position and crankshaft angular velocity.
Setting the correct ignition timing is crucial in the performance of an engine. The ignition timing affects many variables including engine longevity, fuel economy, and engine power. Modern engines that are controlled by an engine control unit use a computer to control the timing throughout the engine's RPM range. Older engines that use mechanical spark distributors rely on inertia (by using rotating weights and springs) and manifold vacuum in order to set the ignition timing throughout the engine's RPM range. There are many factors that influence ignition timing. These include which type of ignition system is used, engine speed and load, which components are used in the ignition system, and the settings of the ignition system components. Usually, any major engine changes or upgrades will require a change to the ignition timing settings of the engine.
Source: Wikipedia.
The two most common terms you'll hear regarding ignition timing are advance and retard. The ignition timing is carefully set so that the spark plug is fired at a specific point in the engine's rotation. In most cases, the spark plug is fired just before the piston reaches top dead center (TDC)--the highest point it can reach in the compression stroke. This is generally expressed in angular degrees, as the piston's position is directly associated with the angular rotation of the crankshaft. When the piston is at TDC, the crankshaft is at 0°.
Advancing the timing means to adjust it so that the plug fires before a specified time. For example, if the factory setting is to fire at 15°BTDC (before top dead center), adjusting it to fire at 20°BTDC would be an advanced setting. Advancing the ignition yields more power, but increases the risk of detonation.
Retarding the timing is the exact opposite: setting the ignition to fire later than the specified time. If the factory setting is to fire at 15°BTDC, adjusting it to fire at 10°BTDC would be a retarded condition. Retarding the ignition usually reduces the chances for detonation, but can cause excessive combustion chamber temperatures, as well as resulting in reduced power output from the engine.
Ignition Power Distribution Control The cylinder pair to be ignited is determined by the ECU from the crank angle sensor (CAS) and top dead center sensor (TDCS; also called the cam position sensor, CPS) signals. The design of the CAS and TDCS changed in 1993. Flash point - the lowest temperature at which vapour of a volatile material can be ignited whit an ignition source present; Values of autoignition temperature are generally higher than flash point, as given for pure hydrocarbons in the tables and figures below. With an increase in. Ignition is a powerful integrated development environment with everything you need to create virtually any kind of industrial application – SCADA, IIoT, MES and beyond – all on one platform.
The most important aspect in concern to ignition timing is detonation. Also known as knocking, pinging, or spark knock, detonation occurs when the combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition from the spark plug, but one or more pockets of air/fuel explode outside the envelope of normal combustion time for the engine. This creates a shock wave in the combustion chamber, which creates a characteristic pinging sound (often equated to dropping rocks or BBs into a Folger's can), and dramatically increases combustion pressure. Consequences range from inconsequential to complete engine destruction.
Detonation should not be confused with pre-ignition.
Detonation is most often caused by running too-low an octane of fuel for the given air/fuel mixture, or advancing the ignition timing too far for safe conditions.
Pre-ignition is a different phenomenon, though similar in behavior and sound (pinging noises). Pre-ignition occurs when the air/fuel mixture ignites before the spark plug fires. Pre-ignition is initiated by hot-spots in the combustion chamber, running a spark plug too hot for the application, or carbon deposits becoming heated from previous combustion events. Pre-ignition is heavily destructive, and in boosted applications can lead to melted and burnt pistons, and can lead to complete engine destruction.
The Z32 comes equipped with a detonation sensor. It consists of a simple peizo microphone that enables the ECU to literally listen for the pinging sound detonation causes. When the ECU detects detonation, it switches to a 'Low Octane' map that uses more retarded ignition timing than the regular maps. In a TT ECU, the wastegate solenoids are also activated, which lowers maximum boost pressure to around 7 PSI.
Setting the ignition timing on the Z32 is simple but VERY vital to good performance and longevity for the engine.
Tools Required:
Image credit: Ash's fantastic writeup, The 6 P's.
There are a few other methods often used and recommended for setting the timing.
The most common difficulty when setting timing is getting the timing light to detect the firing signal through the inductive pickup. This is best resolved with a high tension extension, as noted above.
Another, less common problem, is the inability to set the timing to the specified range. That is, the CAS physically cannot rotate enough to get it to 15 degrees. There are three possible causes for this:
There seems to be a lot of confusion regarding how the Z32 sets its timing, and how to 'adjust' the timing.
In a traditional setup, a car has a distributor which rotates. As it rotates, it bridges a connection to points on the distributor cap--one for each cylinder, and that sends high voltage to the respective spark plugs. These setups allow you to change the ignition timing slightly by rotating the distributor cap, which advances or retards the ignition timing. You can check this setting with a timing light, in a similar fashion as described above.
However, the Z32 doesn't have a distributor. It uses electronic, computer-controlled ignition. While classic, distributor-based ignition systems used elaborate vacuum-variated and centrifugal-weight-based devices to 'tweak' the ignition timing at different engine loads/RPM speeds, the Z32's electronic ignition is completely computer controlled. The ECU contains maps detailing where to set the ignition timing for different engine loads and RPMs. When you have your car tuned, a big part of what the tuner is doing is tweaking the ignition timing maps on the ECU for maximum power and safety.
At idle, under normal circumstances, the ECU sets the timing for 15° BTDC. This is why when you check the timing for the Z32, you're looking for 15° on the crank, and this is correct. Many wrongly assume that this number never changes, and that if it's not flashing at 15°, the CAS needs to be adjusted. However, a lot of times, the ECU isn't timing for 15°.
If, for example, the TPS is set incorrectly, the ECU might not be in 'idle mode,' and time for, say, 20° BTDC, meaning the ECU is trying to fire at 20° BTDC. When the owner checks the timing and sees it's flashing at 20° instead of 15°, he incorrectly assumes that the timing is off by 5° and adjusts the CAS so that the timing light's flash is occurring at 15°. Now when the ECU thinks it's firing at 20°, it's actually firing at 15°, effectively retarding the ignition timing by 5°.
This creates further confusion when owners believe they can check their timing by simply looking at Consult. Consult often reports 15°, so they think their timing is correctly set. The ECU might be timing for 15°, but if the CAS isn't in the right spot, the timing will be off. Checking with Consult only tells you what the ECU is timing for, not what's actually happening under the hood.
The CAS is not a distributor, it's just a sensor, and adjusting the CAS is not the proper method to 'modify' your ignition timing--its only job is to give the ECU an accurate reading on the speed and position of the engine. The adjustment factor is only to ensure that this reading is accurate. The ECU is what adjusts ignition timing, so looking at just one of these factors won't tell you if your timing is right--you have to look at what the ECU is doing in addition to using a timing light to make sure what the ECU is trying to do is actually happening. If the ECU is (for whatever reason) firing at 25°BTDC, the timing light should be flashing at 25°.
Note: This article includes photos of a 1.6l engine. Additional photos of a 1.8 provided by Phil Ethier
The objective here is to change the Cam Angle Sensor (CAS) O ring in about 10 minutes without removing the cam cover.
Have a spare CAS, so we can look at one to see what we are trying to do.
A different view shows the two little “tangs” at the end of the rotating tip.They are slightly off center.
The size of O Ring needed is 1/8” – 1 ½” x 1 3/4”.They run around 59 cents each at about any local auto parts store, or can get this little pack of 4 each for $1.79.As far as I can tell it is made from the same material as the Dealership replacement units.BUNA-N.
Another option is a Viton ring, rated for higher temperatures.
As a side note for those that frequently prefer to change ignition timing, scribe a timing gauge here for different ignition settings.Will only take a moment to change it later and no need for a timing light or engine to warm up.Just remember as the timing belt stretches with age, or belt is replaced, this extra gauge will probably not be accurate.
Remove the 12 mm bolt.Does not matter if the CAS gets rotated slightly since you have the ignition timing marked.Just need to be careful we don’t slide the CAS out of the back of the head during this stage.
Dave let me use this picture of his 1.8 CAS bolt.Little different shape and has a longer bolt head.
Now for a bit of dexterity!Slide the CAS straight back toward the firewall.Do not twist it during removal and try to avoid hitting the tip on anything.
Used pocketknife to cut the old ring off, or when you pry up on it a little, it may shatter and fall behind the engine.Have a new ring handy to fumble in place.The barrel should have enough oil remaining for lubrication.
Note.Many instances it is difficult to remove the CAS from behind the head, but still easy enough to replace ring as shown.
If you see this little space on the barrel between the new O ring and
In this position the new O ring is flush against the yoke.
Why do it like this?