99/00MY OEM ECU Comparison

This article discusses the differences between the various versions of ECU that have been used in the 99/00 model year Subaru Impreza Turbo/WRX/GT throughout the UK, Europe and Australia.

From the dyno plot below, you can see that not all Imprezas are created equal. These tests were done within 30 minutes of each other on the same car - no other changes, only the ECU. Both ECUs are standard original equipment on the same model of car. This car is entirely standard with no modifications.

The two sets of lines on the graph. The lower line is 'power at the wheels' whilst the higher line is 'power at the flywheel'. Swapping an AE802 ECU for an AE801 on this entirely standard car caused the power to rise from 202 to 217BHP !

Checking your ECU Version

The ECU is situated in the passenger footwell of the car, whether RHD or LHD. To check the version of your ECU, simply remove the carpet clips holding the carpet down in your footwell. This will reveal the passenger footwell kick plate. This must now be removed by unscrewing the 4 retaining screws. Lift off the kickplate, and there is your ECU. You can now read the version number from the top of the unit.

ECU Labelling

When viewed externally, the ECUs may be split into two categories:

• Right Hand Drive - RHD ECUs are labelled ae80x, where x is the version number.
• Left Hand Drive - LHD ECUs are labelled ae78x, where x is the version number.

The physical mountings of RHD and LHD units are a mirror image of each other. Other than the mounting differences, and ae78x is functionally equivalent to an ae80x. I.e. for the same value of 'x', the circuit board, software, maps and pin connections are the same. That we have found so far, any version of either RHD or LHD ECU will work in any car, with varying performance results.

Note that STI ECUs will not work in standard cars due to wiring differences, so don't try it. You Turbo/WRX/GT car is also missing the air temperature sensor which STI rely on in their maps.

Aside: ProDrive ECUs for these model years of car were only warrantied in the UK. I have spoken with people who have ProDrive ECUs in mainland Europe, and it appears that the brackets have been adapted from RHD to LHD for sale there. I.e. A left hand drive ProdDrive ECU was never made. Not that it matters though.

Revisions

The following list may not be exhaustive. If you have seen an ECU variant that is not on this list, please contact us so that we can update the information shown here. We have not yet tested an ae780 or ae781, but from the table below, you can see that the pattern is obvious:

Version	RHD ECU Name	LHD ECU Name
1	ae800	ae780 (to be confirmed)
2	ae801	ae781 (to be confirmed)
3	ae802	ae782

Software

The software in an ecu can be split into two categories

• Code - This is the program running inside the ECU.
• Data - This is the maps that determine engine operation including ignition timing, fuelling and boost maps.

Code Versions

There are two code versions that we have seen so far. The ae800 has the earlier version, whilst the ae801 & '802 share a newer code version. The differences are fairly minor.

Data Versions

The are two main versions of data, and they are not paired in the same way as the code versions. The ae800 and ae801 share the same basic mapping data. The newer ae802 has very different maps. There are significant differences in these maps, which goes a long way to explaining the perceived performance differences between seemingly identical cars. The section that follows, highlights these differences.

Map Differences

Fuelling

The newer ae802 runs richer than the older versions. Since the early versions already run rich, this extra fuel will reduce power. The increased fuel will however increase cylinder cooling and move the knock point even further away.

ae800/ae801

ae802

Load 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 03 05 08 0A 0C 0F 12 15 18 1B 1E 21 24 26 28 2A RPM 600 0C 79 79 7A 7C 7E 80 82 82 82 82 82 82 82 82 82 82 800 10 79 79 7A 7C 7E 80 82 82 82 82 82 82 82 82 82 82 1200 18 7B 7B 7C 7F 81 84 86 83 83 83 83 83 83 83 83 83 1600 20 7B 7B 7C 7F 81 83 82 83 83 83 83 83 83 83 83 83 2000 28 7B 7B 7C 7E 80 82 83 83 85 88 88 90 90 90 90 90 2400 30 7C 7C 7E 7E 80 82 83 83 88 98 A8 B0 B0 B0 B0 B0 2800 38 7C 7C 7E 80 80 82 83 8C 98 A0 A8 B0 B0 B0 B0 B0 3200 40 7F 7F 80 80 80 82 84 8C 98 A0 A8 B0 B0 B0 B0 B0 3600 48 80 80 80 80 80 82 82 8C 98 A0 A8 AE AE AE B0 B0 4000 50 80 80 80 80 82 83 88 8B 98 A0 A0 A6 AC AC B0 B0 4400 58 82 82 82 82 84 88 8E 93 98 A0 A2 A6 AC B0 B0 B0 4800 60 84 84 84 85 88 8E 94 9B 9E A0 A4 A8 AE B0 B0 B0 5200 68 87 87 8A 96 97 98 99 9F A5 A8 AB B0 B5 B5 B5 B5 5600 70 92 92 95 9A 9A 9A 9E A5 A8 AC AD B0 B5 B5 B5 B5 6000 78 97 97 9A 9B 9C 9D A2 A6 AC AC AE B2 B5 B5 B5 B5 6400 80 99 99 9C A0 A1 A3 A6 A9 AC AF B1 B5 B5 B5 B5 B5

Load 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 03 05 08 0A 0C 0F 12 15 18 1B 1E 21 24 26 28 2A RPM 600 0C 79 79 7A 7C 7E 80 82 82 82 82 82 82 82 82 82 82 800 10 79 79 7A 7C 7E 80 82 82 82 82 82 82 82 82 82 82 1200 18 7B 7B 7C 7F 81 84 86 83 83 83 83 83 83 83 83 83 1600 20 7B 7B 7C 7F 81 83 82 83 83 83 83 83 83 83 83 83 2000 28 7B 7B 7C 7E 80 82 83 83 85 88 88 90 90 90 90 90 2400 30 7C 7C 7E 7E 80 82 83 83 88 98 A8 B0 B0 B0 B0 B0 2800 38 7C 7C 7E 80 80 82 83 8C 98 A0 A8 B0 B0 B0 B0 B0 3200 40 7F 7F 80 80 80 82 84 8C 98 A0 A8 B0 B0 B0 B0 B0 3600 48 80 80 80 80 80 82 82 8C 98 A0 A8 AE AE AE B0 B0 4000 50 80 80 80 80 82 83 88 8B 98 A0 A0 A6 AC B2 B4 B4 4400 58 82 82 82 82 84 88 8E 94 9E A4 A6 AC B0 B4 B4 B4 4800 60 84 84 84 85 88 8E 96 9E A6 AA AC B3 B7 B7 B7 B7 5200 68 87 94 9A 9D A0 A4 A6 A8 AA B0 B5 BA BA BA BA BA 5600 70 95 95 9A 9E A4 A4 A6 A8 AA B0 B5 BA BA BA BA BA 6000 78 97 97 9B 9F A4 A4 A6 AA AE B4 B7 BA BA BA BA BA 6400 80 99 99 9C A0 A4 A8 AC B0 B0 B4 B7 BA BA BA BA BA

Ignition

The ignition maps on these ECUs differ. All ECU versions have the same high octane ignition map. However, on the more recent (ae802) version, the low octane ignition map is more retarded at high load and high RPM.

ae800/ae801

ae802

Load 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 03 05 08 0A 0C 0F 12 15 18 1B 1E 21 24 26 28 2A RPM 600 0C 0C 0C 10 12 10 0B 07 03 00 00 00 00 00 00 00 00 800 10 0C 0C 10 14 14 0E 09 06 04 00 00 00 00 00 00 00 1200 18 10 10 14 18 1C 19 14 0F 0B 07 07 07 07 07 07 07 1600 20 14 14 18 1C 20 1E 1A 14 10 0E 0C 0C 0C 0C 0C 0C 2000 28 20 20 26 26 26 24 20 1A 14 0F 0C 0C 0C 0C 0C 0C 2400 30 2A 2A 2A 2A 2A 2A 24 1F 1A 15 11 0E 0C 0C 0C 0C 2800 38 2A 2A 2A 2A 2A 2A 24 20 19 15 12 0F 0C 0C 0C 0C 3200 40 2A 2A 2A 2A 2A 2A 28 24 1F 19 17 13 0F 0E 0D 0D 3600 48 2A 2A 2A 2A 2A 2A 2A 28 22 1C 18 14 0F 0E 0D 0D 4000 50 2A 2A 2A 2A 2A 2A 27 24 20 1D 1C 19 15 12 10 0F 4400 58 2A 2A 2A 2A 2A 2A 28 25 20 1D 1C 18 16 14 12 12 4800 60 2C 2C 2C 2C 2A 2A 28 24 1F 1B 19 17 14 13 12 12 5200 68 2E 2E 2E 2E 2C 2C 2C 28 22 20 1F 1D 1B 18 17 17 5600 70 2E 2E 2E 2E 2E 2E 2C 29 27 25 22 20 1D 1B 19 19 6000 78 2E 2E 2E 2E 2E 2E 2E 2B 27 25 23 21 1E 1C 1A 1A 6400 80 2E 2E 2E 2E 2E 2E 2E 2D 29 25 23 21 1E 1C 1A 1A

Load 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 03 05 08 0A 0C 0F 12 15 18 1B 1E 21 24 26 28 2A RPM 600 0C 0C 0C 10 12 10 0B 07 03 00 00 00 00 00 00 00 00 800 10 0C 0C 10 14 14 0E 09 06 04 00 00 00 00 00 00 00 1200 18 10 10 14 18 1C 19 14 0F 0B 07 07 07 07 07 07 07 1600 20 14 14 18 1C 20 1E 1A 14 10 0E 0C 0C 0C 0C 0C 0C 2000 28 20 20 26 26 26 24 20 1A 14 0F 0C 0C 0C 0C 0C 0C 2400 30 2A 2A 2A 2A 2A 2A 24 1F 1A 15 11 0E 0C 0C 0C 0C 2800 38 2A 2A 2A 2A 2A 2A 24 20 19 15 12 0F 0C 0C 0C 0C 3200 40 2A 2A 2A 2A 2A 2A 28 24 1F 19 17 13 0F 0E 0D 0D 3600 48 2A 2A 2A 2A 2A 2A 2A 28 22 1C 18 14 0F 0E 0D 0D 4000 50 2A 2A 2A 2A 2A 29 26 23 1F 1B 19 16 12 10 0E 0D 4400 58 2A 2A 2A 2A 2A 29 26 23 1F 1B 19 17 13 11 0F 0F 4800 60 2C 2C 2C 2C 2A 29 26 21 1C 18 15 13 10 0E 0D 0D 5200 68 2E 2E 2E 2E 2C 2C 29 24 1D 1B 19 18 16 14 13 13 5600 70 2E 2E 2E 2E 2E 2E 2A 25 22 1F 1C 19 16 15 14 14 6000 78 2E 2E 2E 2E 2E 2E 2C 28 24 20 1D 1A 18 17 15 15 6400 80 2E 2E 2E 2E 2E 2E 2C 2A 26 22 1F 1C 19 17 15 15

Boost Control

Boost control on Imprezas uses two main maps. Both are 8x8 in size, though their function is different. These maps are known as 'boost achieve' and 'duty cycle aim'.

The boost maps in these ECU versions are significantly different. In the '802, the maps are progressive. I.e. the higher the engine load, the higher the desired boost. This contrasts with the constant desired boost (for a given RPM, regardless of load) for the '800/'801. Also, note that the RPM scaling maps are significanty different for these ECUs, meaning that the actual RPMs that each row corresponds to differs between ECUs.

Boost Achieve

The boost achieve map specifies the desired shape of the boost curve. The map is two dimensional, and so desired boost can be varied according to both RPM and engine load.

ae800/ae801	ae802
Load 1 2 3 4 5 6 7 8 00 28 30 40 60 80 A0 C0 RPM 0 00 B6 B6 B6 B6 B6 B6 B6 B6 2400 30 B6 B6 B6 B6 B6 B6 B6 B6 3000 3C B6 B6 B6 B6 B6 B6 B6 B6 3400 44 B6 B6 B6 B6 B6 B6 B6 B6 3600 48 B6 B6 B6 B6 B6 B6 B6 B6 5400 6C B0 B0 B0 B0 B0 B0 B0 B0 5800 74 AA AA AA AA AA AA AA AA 6200 7C 9D 9D 9D 9D 9D 9D 9D 9D	Load 1 2 3 4 5 6 7 8 00 3C 46 50 68 80 98 B0 RPM 0 00 87 92 9D A3 AA B0 B6 B6 3000 3C 82 8C 97 9D A6 B0 B6 B6 3800 4C 7A 85 91 9A A3 B0 B6 B6 4600 5C 71 78 82 91 9D AA B0 B6 5000 64 5F 6B 74 80 91 9D AA B3 5400 6C 4C 58 65 70 80 91 A0 B0 5800 74 46 52 5F 6B 7B 8A 9A AA 6200 7C 42 4E 5B 66 78 84 91 9D

Duty Cycle Aim

The duty aim map specifies the 'best guess' duty cycles required to produce the desired boost curve, specified in the boost achieve map. This map allows the ECU to take a guess at the required actuator duty before closed loop control homes in on the boost actually required. Get your aim map too high, and the boost will overshoot. Get it too low, and spool up will be impaired in lower gears.

ae800/ae801	ae802
Load 1 2 3 4 5 6 7 8 00 28 30 40 60 80 A0 C0 RPM 0 00 00 E8 E8 E8 E8 E8 E8 E8 2500 32 D8 D8 D8 D8 D8 D8 D8 D8 2650 35 C8 C8 C8 C8 C8 C8 C8 C8 2800 38 B8 B8 B8 B8 B8 B8 B8 B8 5000 64 C0 C0 C0 C0 C0 C0 C0 C0 5600 70 BC BC BC BC BC BC BC BC 6000 78 B4 B4 B4 B4 B4 B4 B4 B4 6600 84 88 88 88 88 88 88 88 88	Load 1 2 3 4 5 6 7 8 00 3C 46 50 68 80 98 B0 RPM 0 00 00 E8 E8 E8 E8 E8 E8 E8 2500 32 D8 D8 D8 D8 D8 D8 D8 D8 2650 35 C8 C8 C8 C8 C8 C8 C8 C8 2800 38 B8 B8 B8 B8 B8 B8 B8 B8 3800 4C 98 98 98 98 98 B8 B8 B8 5000 64 80 80 80 80 80 BC BC BC 5400 6C 00 20 20 20 50 80 B0 BC 6200 7C 00 20 20 20 50 80 88 88