| 3B Description
| ABY Changes | Schematics
The main differences between
the Motronic system on the 3B and ABY engines are as follows. More details
to follow soon...
- The ABY uses a completely distributorless
ignition system. A pair of ignition packs are used to generate ignition trigger
voltages which in turn generate a high tension spark by means of tiny coil
packs which are located just above each spark plug. This is the main reason
that the rocker covers on the 3B and ABY engines look so different. This distributorless
system was first introduced on the AAN engine (UrS4) and is also used on
the ADU engine (RS2). Similar technology has followed in more recent Audi vehicles from entry level 4-cylinder A3 models to top of the range S8 vehicles and beyond.
- The lack of a distributor on the ABY engine
dictates that the hall effect sensor (G40) resides elsewhere on the ABY engine.
The location of G40 on the ABY is at the timing end of the camshaft where
it provides the same function as on the 3B engine i.e Allowing the ECU to
determine the position of the camshaft to establish a firing point for cylinder-1.
For this reason, the workshop manuals on the AAN engine give G40 the name of
camshaft position sensor (CMP). As on the 3B engine, a faulty (or disconnected)
G40 device will prevent the engine from starting - it will crank forever but
the ECU will not generate any sparks.
- The ABY engine uses slightly higher fuel
pressure and higher flowing fuel injectors than the 3B. The ABY runs at 4.0
bar above manifold pressure whereas the 3B runs at 3.0bar above manifold pressure. Reduce those figures for ~0.5bar for the guage pressure you should see idling due to vacuum in the inlet manifold.
- The ABY injectors utilise a 4-hole pattern for improved vapourisation in
comparison to the 1-hole injectors on the 3B. Even higher rated injectors
are used on the RS2 (ADU) engine in conjunction with a slightly higher rated
fuel pump. As far as I know, the 3B, ABY and AAN engines all use the same
- The pinout of the ECUs on the 3B and ABY
engines is COMPLETELY different. They cannot be interchanged without major
surgery on account of the different ignition systems on the two engines. The
internal software workings of the ABY (AAN and ADU) ECU are somewhat advanced
in comparison to the 3B as they provide much more diagnostic info on the
engine's operation. The 3B ECU only provides visibility of basic settings
via the OBD port, but the ABY has much more intelligence to assist diagnostics.
More details in the VAG-COM section.
- The ECU of the ABY engine has one other fundamental
difference compared to the 3B in that it has a special 'overboost' mode which
allows boost pressure up to a maximum of 1.15bar in short bursts to allow
increased torque to be generated when needed e.g overtaking. Outside of the
'overboost' mode the ABY generates the same 0.83bar of boost as the 3B in
normal circumstances. The overboost mode is limited by the factory ECU to
bursts of no more than fifteen seconds.
- Another intelligent feature of the ABY ECU
is that in the event of failure of the mass air flow meter (MAF) it uses the
throttle potentiometer as a substitite input for determining air flow into
- One significant (though hidden) mechanical
difference between the ABY (AAN / ADU) is the use of a different dual mass
flywheel from the 3B engine. On account of this the 3B and ABY engines use
different clutch components, but I have no details on the reasons why the
3B flywheel was changed for the ABY, AAN and ADU engines. The latter flywheel
is approx three times the price of a 3B item, so the reasons must have been
compelling for someone in Ingolstadt to make such a change.
- Other mechanical differences on the ABY
include a revised oil pump pickup and increased baffling in the sump. The
ABY also has a slightly larger intake manifold than the 3B engine. Differences also apply to the crankcase ventilation system. Finally the ABY engine has a slightly different mechanism for automatic tensioning of
the timing belt.
Last Updated 5th September 2007