Fitting and Tuning a Haltech Interceptor
Tuning a Haltech Interceptor
Tuning a Haltech Interceptor is quite different to tuning a standalone ECU. Although the theories for tuning remain the same in terms of tuning each load point for desired fuel mixture and ignition timing, the response of the factory ECU to Haltech Interceptor changes can be quite different. This section sets out to detail the recommended methods and potential issues that should be considered when tuning an interceptor. This section considers basic tuning theories and methods as assumed knowledge.
Basic Fuel Tuning
The Haltech Interceptor stores corrections in its internal tables as percentages. The actual percentage change applied is a percentage of the signal level. Therefore +100% corrections will double the signal level (not increase it to the maximum), and －100% will reduce the signal level to zero. This gives very high-resolution correction. The actual response of the factory ECU to these corrections is dependent on two main factors: the load sensor type and the factory ECU maps.
MAP and TPS type load sensors will generally give a signal level range from the minimum level to the maximum level at any RPM site. An AFM signal will give the highest signal at the engines max power (high RPM) and the lowest signal at the engine minimum power (low RPM). The result of this is that a smaller signal range is used at any RPM site for the range from minimum load to maximum load. Therefore, when applying corrections to an AFM load sensed factory ECU, small changes (<5%) can make a large difference to fuel mixtures. In contrast, MAP and TPS load sensed factory ECUs often require larger percentage changes (>10%) to get a measurable change in the fuel mixtures.
In addition to the load sensor type affecting the sensitivity, the fuel tables within the factory ECU can also affect the sensitivity. The actual sensitivity is dependant on the fuel mixture variation with load of the factory ECU. Some ECUs tend to enrich the mixture quite aggressively when the load is detected above a normal level as a safety response. Unfortunately the results can be quite non-linear, and sometimes some trial and error is required. Because the Haltech Interceptor has a very high resolution of fuel control with variable load and RPM sites, the desired fuel mixture curves can be achieved with some tuning time.
Closed Loop Mode
Most factory ECUs use closed loop control of injection times at light loads. This means that the actual injection times are calculated after monitoring the exhaust mixtures with the O2 sensor. This is generally only done at light loads (cruising, idle) with a stoichiometric fuel mixture.
During closed loop mode, the factory ECU only uses the engine load sensor for the base injection time, and it then applies corrections to this time to get the mixture to stoichiometric. The impact of this on the Haltech Interceptor is that the factory ECU will tune around any fuel corrections made whilst in closed loop mode as it attempts to get back to stoichiometric fuel mixtures. If large corrections are made in the Haltech Interceptor fuel tables during the factory ECU closed loop mode, the factory ECU could generate a fault code if the closed loop corrections it must do fall outside of its normal expected range. It is recommended that fuel corrections done in closed loop mode should only be done to bring the tune closer to stoichiometric fuel mixtures. This may even be necessary if mechanical modifications have been made, resulting in the factory ECU base maps being well away from the required stoichiometric fuel mixture. Modifications that would likely cause this are: larger injectors, higher fuel pressure, modified cams etc.
Basic Ignition Tuning
Haltech Interceptor ignition tuning is quite consistent in its response across all vehicle applications. The units in the internal tables are in degrees that are then added to the ignition timing generated by the factory ECU ignition tables. It is important to realise that the ignition tables are a correction, and not the actual ignition timing being run. The factory ECU should be quite close to the desired ignition timing on an unmodified car, but performance gains can be made if tuning for higher quality fuels or the factory ECU tune is very conservative. If the engine is modified, large power gains may be possible. As always, it is important to monitor for any pinging that may occur with too much ignition advance.
Unlike fuel corrections, ignition corrections can generally be made at any load and RPM site, as there is no closed loop control of ignition timing. Often the factory ECU can be very conservative at light loads, and noticeable gains in throttle response can be achieved with additional ignition advance in these areas.
Knock Control
Many factory ECUs employ knock control to prevent engine damage due to pinging. Generally the factory ECU will monitor pinging using the knock sensor and retard ignition timing to get rid of it. The problem with this for the Haltech Interceptor is that in the quest for more power, a tuner may advance the ignition timing, but this may cause pinging. The factory ECU then retards the timing to get rid of the pinging, and the result is that the power curve becomes inconsistent and makes no more power. Haltech recommends that before applying advance, the tuner should retard the ignition timing to see if power is lost. If power is lost, then the advance can be gradually added until max power is reached. It is recommended that the tuner run the minimum advance that achieves the performance requirements. Haltech has found on several cars that maximum power was achieved with ignition retarded from the factory ignition curves, as the factory ECU was tuned to run on the verge of knock control all the time. Therefore more power was made by pulling the ignition advance back to a level that would prevent knock control operation and still make good power.
Diagnostic Scan Tools
Haltech strongly recommends the use of diagnostic scan tools to aid in the tuning of the Haltech Interceptor. Some of the issues mentioned above can be easily diagnosed and worked around with knowledge of the correction factors and modes of the factory ECU. The following parameters can be very useful whilst tuning a Haltech Interceptor:
- Fuel Mode － Often a parameter is available that indicates if the ECU is in closed loop mode or open loop mode. This aids in preventing factory ECU errors resulting from applying inappropriate corrections whilst in closed loop mode
- Long Term Fuel Trim － Often factory ECUs monitor the closed loop control corrections, and if they average away from 0%, a long term fuel correction is added to enable the closed loop to work with a base injection time that is close to correct. This is to allow the system to maintain correct operation as mechanical parts wear and affect the fuel mixtures. Sometimes mechanical modifications can change the long-term fuel correction significantly (larger injectors), and this could cause fault conditions. If the tuner monitors the long term fuel correction, they can tune to minimize this value to prevent any ECU fault conditions
- Ignition Timing － This parameter is useful to give the tuner the ability to know the actual ignition timing being run. Note that the actual ignition timing is this value added to the interceptor correction value.
- Knock Control Retard － This parameter indicates if the factory ECU is retarding ignition in response to detection of pinging. It is recommended that the tuner adjust the tune so that pinging does not occur in normal circumstances in order to get a consistent power curve.
There are many generic scan tools available now that support a wide range of vehicles. It may be necessary to research into the best scan tool to suit the vehicles that are dealt with most commonly.