As requested by gorganl2000 below is some background information on the TCCS electronic spark advance system.
Spark Advance Control
The advent of ECU spark management systems provides more precise control of ignition spark timing. The centrifugal and vacuum advances of conventional systems are eliminated, in their place are the engine sensors which monitor engine load (PIM) and speed (Ne). Additionally, coolant temperature, detonaton and throttle position are monitored to provide better spark accuracy as these conditions change.
To provide for optimum spark advance under a wide variety of engine operating conditions, a spark advance map is developed and stored in a look up table in the ECU. This map provides for accurate spark timing during a combination of engine speed, load, coolant temperature and throttle position while using feedback from a knock sensor to adjust variations in fuel octane.
The Spark Advance Control system maximizes engine efficiency by continuously adjusting spark advance timing to deliver peak combustion pressures when the piston reaches about 10' after TDC. Incorrect spark timing can have a significant effect on emission output and vehicle driveability. If ignition timing is excessively advanced during certain conditions, detonation will occur resulting in increased HC and NOx levels. Since NOx production is most predominant under loaded engine operating conditions, the spark advance system must ensure accurate ignition timing during these conditions. If ignition timing is incorrectly retarded, only partial combustion will take place resulting poor engine performance and increased emission levels.
Electronic Spark Advance Operation
For maximum engine output efficiency, the air/fuel mixture must be ignited so that maximum combustion pressure occurs approximately 10°-15° after TDC. As engine RPM increases, there is less time for the mixture to complete its combustion at the proper time because the piston is travelling faster. The ECM controls when the spark occurs through the IGT signal. By varying the time the IGT signal is turned off, the ECM changes ignition spark timing.
Causes of Incorrect Spark Timing
For systems that use the ECM to compute ignition spark advance, there are only two conditions which are likely to cause spark timing to be incorrect; initial timing or a false input signal to the ECM.
The first step in troubleshooting emissions and driveability concerns should always include a quick check of initial ignition timing. Any error in initial timing will be reflected throughout the entire spark advance curve. If engine load is miscalculated because of incorrect input signals, the spark advance angle will not be appropriate for engine operating conditions. This will result in driveability and emission problems.
Effects of Spark Advance on Emissions and Driveability
•Too much spark advance, particularly during high engine load conditions, increases the likelihood of engine detonation and increases combustion temperature and pressure. This results in an increase in HC and NOx output, decreased engine performance, and possible permanent damage to the engine.
•Too little spark advance causes only partial combustion of the air/ fuel charge, resulting in very poor engine performance and fuel economy. Partial combustion will also result in an increase in CO levels.
Functional Testing
Spark advance problems can result from an incorrect initial timing setting or a problem with spark advance during operation. Before attempting to check spark advance during operating conditions, the initial or "base" ignition timing setting should checked and adjusted. This procedure varies between systems, but on TCCS equipped vehicles, it generally requires jumping terminals at an underhood check connector (DLC1) to default the TCCS system to initial timing. After checking or adjusting initial timing, remove the test wire to inform the ECM to re-establish corrective control over timing.
Even with initial timing correct, it is still possible that the system is miscalculating ignition timing as a result of incorrect sensor inputs. For example, if a MAP sensor indicates light engine load, when in fact, the engine is experiencing high engine load, the ECM may incorrectly respond by over advancing ignition timing to the point of causing detonation. If inaccurate sensor inputs are suspected, it is recommended that standard voltage checks are performed of all major sensor inputs to the ECM. Compare these readings to those listed on the standard voltage chart on the Repair Manual or readings obtained from other known good vehicles. Some of the more important spark control parameters include engine speed, engine load, throttle angle, and coolant temperature.
NE Signal and G Signal
The NE signal indicates crankshaft position and engine RPM. The G signal provides cylinder identification. By comparing the G signal to the NE signal, the ECM is able to identify the cylinder on compression. This is necessary to calculate crankshaft angle (initial ignition timing angle), identify which coil to trigger on Direct Ignition System (independent ignition), and which injector to energize on sequential fuel injection systems.
Starting Ignition Control
Ignition timing control consists of two basic elements:
• Ignition control during starting
• After start ignition control
Ignition Control During Starting
Ignition control during starting is defined as the period when the engine is cranking and immediately following cranking. The ignition occurs at a fixed crankshaft angle, approximately 5°-10° BTDC, regardless of engine operating conditions and this is called the initial timing angle.
Since engine speed is still below a specified RPM and unstable during and immediately after starting, the ignition timing is fixed until engine operation is stabilized. The ECM recognizes the engine is being cranked when it receives the NE and G signal. On some models, the starter (STA) signal is also used to inform the engine is being cranked.
After-Start Ignition Control
After-start ignition control will calculate and adjust ignition timing based on engine operating conditions. The calculation and adjustment of ignition timing is performed in a series of steps, beginning with basic ignition advance control. Various corrections are added to the initial ignition timing angle and the basic ignition advance angle during normal operation. After-start ignition control is carried out during normal operation.
The various corrections (that are based on signals from the relevant sensors) are added to the initial ignition timing angle and to the basic ignition advance angle (determined by the intake air volume signal or intake manifold pressure signal) and by the engine speed signal:
Ignition timing = initial ignition timing angle + basic ignition advance angle + corrective ignition advance angle
During normal operation of after-start ignition control, the Ignition Timing (IGT) signal is calculated by the microprocessor in the ECM and output through the back-up IC.
Basic Ignition Advance Control
The ECM selects the basic ignition advance angle from memory based on engine speed, load, throttle valve position, and engine coolant temperature.
Relevant Signals:
• Intake air volume (Intake manifold pressure (PIM)
• Engine speed (NE)
• Throttle position (IDL)
• Engine Coolant Temperature (THW)
Corrective Ignition Advance Control
The Corrective Ignition Advance Control makes the final adjustment to the actual ignition timing.
Warm-Up Correction
The ignition timing is advanced to improve driveability when the coolant temperature is low. In some engine models, this correction changes the advance angle in accordance with the intake manifold pressure and can advance approximately 15° by this correction during extremely cold weather.
Over Temperature Correction
To prevent knocking and overheating, the ignition timing is retarded when the coolant
temperature is extremely high. The timing may be retarded approximately 5° by this correction.
Relevant Signals:
• ECT - THW
• MAP - PIM
• Engine Speed - NE signal.
• Throttle position - IDL
Stable Idling Correction
When the engine speed during idling has fluctuated from the target idle speed, the ECM adjusts the ignition timing to stabilize the engine speed. The ECM is constantly calculating the average engine speed. If the engine speed falls below the target speed, the ECM advances the ignition timing by a predetermined angle. If the engine speed rises above the target speed, the ECM retards the ignition timing by a predetermined angle. This correction is not executed when the engine exceeds a predetermined speed. In some engine models, the advance angle changes depending on whether the air conditioner is on or off. In other engine models, this correction only operates when the engine speed is below the target engine speed.
Torque Control Correction
This correction reduces shift shock and the result is that the driver feels smoother shifts. With an electronically-controlled transaxle, each clutch and brake in the planetary gear unit of the transmission or transaxle generates shock to some extent during shifting. in some models, this shock is minimized by delaying the ignition timing when gears are upshifted. When gear shifting starts, the ECM retards the engine ignition timing to reduce the engine torque. As a result, the shock of engagement and strain on the clutches and brakes of the planetary gear unit is reduced and the gear shift change is performed smoothly. The ignition timing angle is retarded a maximum of 20° by this correction. This correction is not performed when the coolant temperature or battery voltage is below a predetermined level.
Relevant Signals:
• Engine Speed (NE)
• TPS (VTA or IDL or PSW)
• ECT (THW)
• Battery voltage (+B)
Air/Fuel Ratio Correction
The engine is especially sensitive to changes in the air/fuel ratio when it is idling, so stable idling is ensured by advancing the ignition timing in order to match the fuel injection air/fuel ratio feedback correction. This correction is not executed while the vehicle is being driven.
Relevant Signals:
• Oxygen sensor.
• TPS (VTA or IDL).
• Vehicle Speed (SPD).
Knock Correction
Engine knock, if severe enough, can cause engine damage. Combustion chamber design, fuel octane, air/fuel ratio, and ignition timing all affect when knock will occur. Under most engine conditions, ignition timing needs to be near the point when knock occurs to achieve the best fuel economy, engine power output, and lowest exhaust emissions. However, the point when knock occurs will vary from a variety of factors. For example, if the fuel octane is too low, and ignition takes place at the optimum point, knock will occur. To prevent this, a knock correction function is used.
When engine knock occurs, the ECU monitors the knock sensor signal feedback to determine the degree of detonation taking place. This is accomplished by filtering out sensor signal voltage which does not go above preprogrammed amplitude parameters. Because other background noise and vibration cause some signal output from the knock sensor, the ECU is also programmed to filter out any signal which does not fall within certain frequency ranges.
When the ECU judges that detonation is taking place, it retards ignition timing until the knocking stops. Timing is then advanced back to a calulated value or, if dentonation continues, retarded again until detonation is stopped. In this manner, the ignition system can be operated at maximum efficiency, on the borderline of detonation, while avoiding and audible 'ping'. In the event that the ECU continues to sense detonation, timing retard is limited based on a clamp value stored in memory. If the ECU determines that the knock retard is not functional, it will enter a fail-safe mode and fix the retard angle to prevent engine damage.
Some mechanical problems can duplicate engine knocking. An excessively worn connecting rod bearing or a large cylinder ridge will produce a vibration at the same frequency as engine knocking. The ECM in turn will retard the timing.
Maximum and Minimum Ignition Advance Control
If the actual ignition timing (basic ignition advance angle + corrective ignition advance or retard angle) becomes abnormal, the engine will be adversely affected. To prevent this, the ECM controls the actual advance so that the sum of the basic ignition and corrective angle cannot be greater or less than preprogrammed minimum or maximum values.
Approximately, these values are:
• MAX. ADVANCE ANGLE: 35°-45°
• MIN. ADVANCE ANGLE: 100°-00°
Advance angle = Basic ignition advance angle + Corrective ignition advance angle
The Effects of Fuel Octane
Toyota engines equipped with a knock detection system are very sensitive to fuel octane levels. Motor fuels with low octane ratings will cause the engine to detonate, which will in turn, cause the detonation retard system to retard timing. An adaptive memory factor is used to track signals from the knock sensor.
When detonation occurs frequently, the ECM relearns the basic spark advance curve, retarding spark throughout the entire engine operating range. This retarded spark curve will negatively effect engine performance and fuel economy under all driving conditions, even after a tank of higher octane fuel is purchased. The retarded spark curve will remain stored in the ECM keep alive memory until the engine is operated for a substantial amount of time on the higher octane fuel, or until the "keep alive memory" is cleared by removing power from the BATT terminal.
i use an AEM one. im using adj. fpr at 2.3 bar (as stock), at idle afrs are between 14.7-15.2 and on boost 0.9(wot) mid to high 10s. nt bad but prefer it in 11s, either than that it fuels very gd when coming on boost etc quite satisfied with it
