How a TD5 starts.

Here is a little teaser for you TD5 fans....
Being that the TD5 only has a crank sensor and no cam sensor,(Unlike the BMW engines in TD4 and TD6.) how does the ECU know when piston 1 is on the correct stroke,(IE firing stroke,not inlet stroke.) to commence injection and fire it up ?
I think I know how it does it but I wondered what others thought or indeed know.

eightinavee said:

Here is a little teaser for you TD5 fans....
Being that the TD5 only has a crank sensor and no cam sensor,(Unlike the BMW engines in TD4 and TD6.) how does the ECU know when piston 1 is on the correct stroke,(IE firing stroke,not inlet stroke.) to commence injection and fire it up ?
I think I know how it does it but I wondered what others thought or indeed know.

Click to expand...

From RAVE:

The CKP sensor is located in the transmission housing with its tip adjacent to the outer circumference of the
flywheel. The CKP sensor works on the variable reluctance principal, which sends a signal back to the ECM in the
form of an ac voltage.
The ECM uses the signal from the CKP sensor for the following functions.
• To calculate engine speed.
• To determine engine crank position.
• To determine fuel injection timing.
The CKP sensor works as a Variable Reluctance Sensor (VRS). It uses an electromagnet and a target ring to
generate a signal. As the target ring passes the tip of the CKP sensor the magnetic field produced by the sensor is
cut and then re-instated. The ECM measures the signal as an ac voltage.
The outer circumference of the flywheel acts as the target ring for the sensor. The flywheel is divided into 36
segments, each of 10deg. 31 segments have drilled holes and 5 segments are spaces. This equals 360deg or one
engine revolution. The 5 spaces correspond to the TDC position of the 5 cylinders. This allows the ECM to control
fuel injection timing for each of the cylinders.

Ratty,you need to read the question again.

eightinavee said:

Ratty,you need to read the question again.

Click to expand...

I was under the impression that it knew it was on the firing stroke not the inlet stroke by the position of the flywheel segements without holes as explained in my post above.

The 5 spaces correspond to the TDC position of the 5 cylinders. This allows the ECM to control
fuel injection timing for each of the cylinders

Click to expand...

ratty said:

I was under the impression that it knew it was on the firing stroke not the inlet stroke by the position of the flywheel segements without holes as explained in my post above.

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Yea,but the flywheel turns 360 degrees twice for the four stroke cycle,so how does the ecu know which of the two it is ?

eightinavee said:

Yea,but the flywheel turns 360 degrees twice for the four stroke cycle,so how does the ecu know which of the two it is ?

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AAAAH that's easy. The missing holes are placed unevenly around the circumference of the flywheel. By having
the crankshaft drilled in a unique sequence, the ECM is able to determine its position in the engines cycle within a
maximum of 130th of crankshaft rotation.

Yer still not gettin it,start with the piston on # 1 going down the bore on the inlet stroke - the crank sensor is reading the same flywheel segment sensor signals as it will after the piston has gone back up on the compression stroke and is then belted back down on the firing stroke.
So how does it know ?

eightinavee said:

Yer still not gettin it,start with the piston on # 1 going down the bore on the inlet stroke - the crank sensor is reading the same flywheel segment sensor signals as it will after the piston has gone back up on the compression stroke and is then belted back down on the firing stroke.
So how does it know ?

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what you mean is that the top end knows what the bottom end is doing due to the position of the followers but how does the bottom end know what the top end is doing? Correct?

ratty said:

what you mean is that the top end knows what the bottom end is doing due to the position of the followers but how does the bottom end know what the top end is doing? Correct?

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That be it .

provided the ECU is told the initial starting conditions, then it should inject on every other pulse from the relevant segment.

Treworgey 90 said:

provided the ECU is told the initial starting conditions, then it should inject on every other pulse from the relevant segment.

Click to expand...

So what tells it ?

Treworgey 90 said:

provided the ECU is told the initial starting conditions, then it should inject on every other pulse from the relevant segment.

Click to expand...

In theory as the engine is in TDC when the timing chain is fitted it would already know it's position. In practice it could lose it's position if the engine was turned by hand while switched off for example. There has to be some way of it knowing what it's doing should the engine be rotated once off.

ratty said:

In theory as the engine is in TDC when the timing chain is fitted it would already know it's position. In practice it could lose it's position if the engine was turned by hand while switched off for example. There has to be some way of it knowing what it's doing should the engine be rotated once off.

Click to expand...

Now yer thinkin,plus what happens if you let the handbrake off with it in gear and the car moves a bit turning the engine whilst the ignition is off so the ecu is dead - wot happens then ?

What is a 'Crankshaft Sensor'?

A Crankshaft Sensor (also known as a Crankshaft Angle Sensor - or CAS for short) watch's the position of the camshaft and its relationship with the piston position inside the engine. The CAS is an inductive signal generator, it measure reluctance. The CAS is typicality found on injection engines, and its an important sensor. Without it, the engine will not run at its optimum, and if faulty, the ECU warning light shall illuminate on the dash.

How does a CAS work?

The CAS is typically positioned beside the cam belt or crankshaft (Figure 1). A number of steel pegs or steps (i.e. different thickness of material) are set at regular intervals around the circumference of the flywheel or crankshaft (Figure 7). Typically a pin or a step may be set at every 10° (but this number does vary depending on what the engine is). The flywheel thus becomes a reluctor.

A permanent magnet, which acts as a inductive signal generator, is mounted in close proximity to the flywheel. This radiates a magnetic field. As the flywheel spins and the pins or steps are rotated in this magnetic field, an alternating (AC) waveform output signal is produced and the EMU (Engine Management Unit) uses this information to calculate the speed of rotation.

If a pin is omitted at two points on the flywheel the signal also changes at these points, and a reference to TDC (Top Dead Centre) will be returned to the EMU. The location of the position signal is not TDC, but may be at 90° BTDC (or some other point fixed by the vehicle manufacture - depending on engine type).


TDC stands for Top Dead Centre. Its a termed used to express the position of the piston head within its stoke, i.e. its maximum compression stage. At TDC, the spark plug should be ready to ignite the fuel within. BTDC stands for Before Top Dead Centre.

In addition as the flywheel spins, the missing pins or double pins cause a variance of the signal which is returned to the ECU as reference to the TDC position.

Although most modern systems utilise a single CAS, some older systems use two CAS - one for the RPM (Revs per Minute) and one for the position. The 2L 16v C20XE engines commonly use this system (as found in the Cavalier, Calibra and Astra GTE's). The waveform produced by each type of CAS will be slightly different.

The peak-to-peak voltage of the speed signal varies according to engine speed, the faster the rotation, the bigger increase in voltage produced (Figure 8). For example it can vary from 5 volts at idle to over 100 volts at 6000rpm. Because the EMU is a computer, its works on digital information (on or off signals). The output signal produced by a CAS is analogue, which isn't compatible with the EMU. So the EMU uses a ADC (Analogue to Digital Convertor) which transforms the AC pulse into a digital signal.

When used the CAS provides the primary signal to initiate both ignition and fuelling.

eightinavee said:

Now yer thinkin,plus what happens if you let the handbrake off with it in gear and the car moves a bit turning the engine whilst the ignition is off so the ecu is dead - wot happens then ?

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This is purely a guess. Does the position of the 3 bronze links in the timing chain help acertain the cycle it's on?

ratty said:

This is purely a guess. Does the position of the 3 bronze links in the timing chain help acertain the cycle it's on?

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Now yer tekin the pi--,I have to sleep,I'm knacked - just finished doing an engine fit in an 8.9 ltr Cobra replica.

eightinavee said:

Now yer tekin the pi--,I have to sleep,I'm knacked - just finished doing an engine fit in an 8.9 ltr Cobra replica.

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snigger

magic + ignition key

Int injection timing set by the lobe on the camshaft. crank sensor just adjusts fuelling depending on RPM