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ENGINE MANAGEMENT
The electronic control unit on this car is found inside the vehicle, behind
a trim panel the bonnet on the left of the front passenger's footwell.It
features no fewer than five separate connectors. Other primary components
include
The beauty of this Bosch management system is that it's essentially a very straightforward set-up.
The only really complicated aspect is the 'fly-by-wire' throttle control system.
While this is normally reliable, when problems do occur they are more awkward to put right
than on a conventional system. When things do start to go wrong Simon says that the most common
telltale sign is that the engine will lose its ability to rev. It will tick over quite happily and
very evenly, but acceleration will be impossible. This is an easy problem to spot, but can be
rather more time consuming to actually confirm. The system must be tested manually with careful
voltage measurement. You need to observe the varying voltage being sent to the ECU from the
throttle position sensor at the pedal. In the worst cases, there will be no voltage output at
all and the switch will have defaulted to its basic setting which will be sufficient to keep
the engine at idle (0.4-0.5V).
In many cases you will find this Alfa engine to be cleaner than most, thanks to the fact that
it is completely enclosed from below by a bolt-on undertray, which keeps road dirt and moisture
at bay. Nevertheless, carry out all the usual pre-diagnostic checks for obvious signs of trouble.
Work your way around the engine looking for loose or damaged connectors, split rubbers,
missing clips etc. In the case of a non-runner, never forget the basics.
The car is fitted with an engine immobiliser, activated by an electronic chip on the
ignition key fob. This system has its own control unit and if the dashboard warning light
remains flashing during cranking,
then suspect an immobiliser problem. Never ignore the possibility of something as simple as a
blown fuse, or the chance that the inertia switch might have been triggered by an impact of
some sort. It's also worth knowing that there is an important earth connection point inside the
boot, and another under the bonnet, close to the relay box. Check that both of these are clean
and securely located to ensure a good contact and an efficient earth. The same warning light on
the dashboard, which informs about immobiliser problems (marked with a fuel injector symbol),
doubles as a fault indicator as well. Unfortunately, its only function in this respect is to
highlight that a fault has been registered - it remains lit. No clue is given about the cause of
the problem, and the system must be interrogated using specialist diagnostic equipment if an
answer is to be found.
Thankfully, this type of failure is extremely
rare. If either the sensor or the actuator are found to be faulty then replacement is the only
solution. This is a simple nut and bolt job, although Simon says that a new pedal sensor is
£190 while the actuator costs £400. Knock sensor failure can be a hard problem to detect on an
engine like this. There are two of these sensors used on this V6, and the failure of one will
present no clues apart from lighting the engine management warning lamp on the dashboard.
You certainly won't hear the engine knocking in the old-fashioned way. Obviously, illumination
of the warning lamp means that the fault code memory will have to be interrogated to identify
the specific problem. Once the offending component has been identified, testing it involves
using an oscilloscope or a digital voltmeter. It's a relatively simple procedure. Connect the
scope to either one of the knock sensor's two signal wires (the third wire has a braided screen
and is easily identifiable) and, with the ignition switched on, use a metal object to gently tap the
sensor. What you're looking for is a tiny voltage output which is generated in response to the
tapping. To register this the scope must be set on a very low voltage scale (maximum 200mV), and
the signal will be clearly visible. There is no ideal output to check for here, the important point is
that there is one at all - anything will do! The most common problem with knock sensors is that they
get broken. They are bolted directly on to the engine block and so, with time, suffer the effects of vibration.
Once they've packed up replacement is the only answer, and Simon says that new ones cost about £50. The final
problem concerns the ignition system. This engine is fitted with six coils, one for each spark plug. While these
units are relatively reliable, problems do occur and they do fail .Normally when this happens, the resultant misfire
will be noticeable, although it's always harder to spot such defects on a six-cylinder engine, compared to a
four. Another practical pointer is a higher than normal HC emission reading from the exhaust. Identifying the
faulty coil is relatively straightforward. All the injectors on this engine are individually connected and access
to them is good. The best way to identify the problem is to disconnect one injector after another, Secondary -
5.0-8.0 Kohms and note which of them has the greatest effect on lowering the HC emissions value. In some cases,
faults like this may well be intermittent. This type of problem can be more noticeable because the engine hesitation,
when it occurs, will be obvious and the motor may even come close to stalling. This is caused by the ECU's
attempts to sustain the faulty coil. Back-feeds to the ECU from the faulty coil cause it to momentarily switch off,
in an effort to protect itself from damage. As the problem develops there will come a point when the engine will
simply stop, and will have to be restarted using the key. Then once the coil fails completely the engine will
revert to five-cylinder operation, and ironically will probably become smoother again. Coil failure is essentially
an age-related problem and is therefore very difficult to predict. Simon says that most will last for well over
100,000 miles but that he has known some fail after just 35,000. But it is important to realise that one failure
does not mean that the rest are sure to follow. Replacements cost about £60 each and are very easy to fit. Each is
held in place with four bolts, although those at the rear are much more awkward to reach because the
inlet manifold has to come off first, to gain access. If the car you are looking at is suffering with a
definite misfire and you are unable to pin the cause down with an HC emissions check because the fault is not
regular enough, or perhaps only occurs when the car is being driven, then try the following testing procedure.
Remove the plastic protectors which cover the coils on the front and rear cylinder banks - this is part of the inlet
manifold at the rear, so the whole lot will have to be stripped off. Remove each of the six coils and measure the
resistance across each one, and their end caps (which fit on to the spark plugs). Hopefully, this systematic test
will highlight one coil which has gone open-circuit, or which is displaying a noticeably higher resistance than the
rest. Under normal circumstances the primary coil resistance should be just below one ohm, around the 0.8ohm mark.
The secondary resistance should be about 12,000-15,000ohms. The end cap will usually have a resistance of about
1,000ohms. Any significant departures from these figures should arouse your suspicions.
Crank Angle Sensor: 1200 ohms Approx
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