20V 4AGE Engines and Aftermarket ECU's
Covering some of the common and smaller pieces of information covering the interfacing of aftermarket ECU's to 20V 4AGE engines.
Most 20V conversions are for a rear wheel drive form so the original distributer cap needs to be removed as discussed in the 20v RWD Guide, this means that multiple coils are needed for the ignition system. So from the ECU side two ignition outputs in a waste spark setup or four for independent coils.
Both 20V engines have very large diameter throttle blades for their displacement. This means there is very little of a vacuum signal for a map sensor. While it is possible to tune using a MAP sensor many instead use purely a throttle position sensor with map compensation from things such as water and air temperature. This is how the SQ Engineering AE86 is tuned and it has good smooth power and economy. However for a good tune a fuel map that has a decent resolution is suggested, such as better than every 500RPM points.
VVT is ideally turned on at a low revs and off at higher revs. This means if the aftermarket ECU in question has the option of turning an output on/off at a set revs and then the reverse at higher revs then a single relay can be used. The relay would ground the second side of the VVT solenoid and would be triggered directly. For an ECU that can only switch the output once at a certain set revs then two outputs are needed. Each of the outputs would turn on a relay each, where the first relay would activate the VVT solenoid and the second cut the power to the first. This is discussed in the working with VVT guide.
Crank angle sensor interface:
The inductive signal sent from either of the 20v crank angle sensors is quite weak and prone to noise induced issues. This can cause sudden shuttering or idle issues. Consult the maker of the ECU before buying in regard to this issue.
The OEM 20V idle control solenoid (ISCV) is located near the fourth throttle bolted to the side of the head. This uses opposing magnetic fields to adjust the opening of an air-bypass between the air-box and the intake manifold. This may not be able to be controlled by some ECU's. A 20v engine can be run with any form of idle control without any major issues however the original ISCV has to be totally removed in advance. This is because without the signals from the original ECU the opening in the solenoid can drift from being open to shut causing idle issues to at worse the wrong tune if tuned when open. The other option is the idle control valve off another manufacturer, consult the maker of the ECU for a common compatible model.
Adaptronic specific information:
The Australian Adaptronic ECU is a very popular and proven choice of ECU for running 20V engines. It is well supported and affordable, the replacement looms are particularly well priced. To find out more: Adaptronic.com.au or the message boards.
There is a problem noted with the 20v crank angle sensor where the engine will not rev past 7000 RPM, the fix is addressed here.
Change in power/driveability:
All 20V ECU's are over 20 years old now and there have been many reports of leaking capacitors. This can cause the engine to run less than ideal (see below). It has also been discovered that the OEM tune for either 20V ECU's is best described as being very conservative. They are known for having very retarded (no pun intended!) timing and running very rich above a certain revs or load.
Results with the SQ Engineering AE86: This was originally run with an OEM Silvertop ECU before being changed to another of the same model with the capacitors all changed. This 'recoed' ECU let the engine run better in terms of power overall however it was still very unpredictable and as such the engine had significantly more power on some days than others. The exhaust note witnessed from outside the car also had a very harsh and unpleasant rasp sound. The inside sound can be heard in the videos in it's worklog.
At a later date a Wolf 4.1 ECU was installed, the difference was nothing short of astonishing. It was tuned solely for 98 Octane (Australian 98 rated) fuel. The whole rev range had a large increase in power, in particular the mid range. Previously the torque curve just curved from a low point steadily upwards. The change afterwards was a massive and flat torque curve. From 3000 to 5500 revs the torque 'curve' was a dead flat line. Even with the VVT solenoid temporarily unplugged it still has more power over the whole rev range than the previous ECU.
This had a profound effect on the driveability of the car in that it became highly responsive and very easy to drive, there is still no hill yet driven up that needed more than 3000 revs. Even off idle the car previously was quite easy to stall, afterwards even with rough clutch use it would still not stop the engine.
Interestingly the engine note also completely changed. The raspy exhaust note was replaced with a lower pitch more even 'roar'. This was due to the more advanced ignition timing.