Peugeot Forums banner
1 - 12 of 12 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter · #1 ·
I don't have a problem to solve, just curious about something I read and want to expand my knowledge.
Just read that my 206 1.4 uses the wasted spark ignition system. As I didn't know what that was I did some research. The crankshaft position sensor tells the ECU when two of the pistons are at (or near) TDC but as the car does not have a camshaft position sensor it cannot tell which of these two cylinders is on the firing stroke so it sparks both of the plugs. The spark is wasted on the cylinder on the exhaust stroke hence the term wasted spark ignition.
The thing that puzzled me was that how does the engine know which injector to fire. I struggled to find a definite answer but did come across a suggestion that as well as both sparks firing, both injectors fire as well. So for every "cycle" of the engine each injector fires twice, putting in half of the required fuel load each time. If the inlet valve is shut when the injector fires the fuel just sits around until the inlet valve opens and is then sucked in with the other half of the fuel load.
Does anyone know if this is the correct answer to this question.
 

·
Registered
Joined
·
15,376 Posts
No that is wrong as if you fired in fuel on the cylinder not on compression it would go straight out the exhaust !!

Injectors are fired individually its only possible to fire coils in pairs due to the way the engine works.

Its a wasted spark system simply for design simplicity nothing more most cars with coil packs use wasted spark systems
 

·
Registered
Joined
·
2,536 Posts
If the engine has a crankshaft position sensor but no camshaft position sensor, how does the engine ECU know which of the two cylinders is on the inlet stroke, so that it can operate just that injector?
 

·
Moderator
Joined
·
9,537 Posts
It does not need to, the two cylinders are two cycles apart so one cylinder is on exhaust stroke and one compression so it does not matter which is which, one will be ready to fire.

On some models firing cylinder is identified by ecu sensing cylinder via spark plug after firing by looking for ionised air from combustion process
 

·
Registered
Joined
·
1,140 Posts
No that is wrong as if you fired in fuel on the cylinder not on compression it would go straight out the exhaust !!

Injectors are fired individually its only possible to fire coils in pairs due to the way the engine works.

Its a wasted spark system simply for design simplicity nothing more most cars with coil packs use wasted spark systems
No, this is only correct if the engine has direct injection into the cylinder, not into the manifold as is the case here.

If the injection is into the manifold, the fuel will simply hang around in the manifold until the inlet valve opens.

There are plenty of engines [particularly older ones] that employ this system as standard. One that springs to mind is the M20 6 cylinder BMW motor- it injects to 3 cylinders at the same time using a basic signal off the no 6 spark plug wire to determine which bank of 3 to fire at any one time. If this signal disappears due to a faulty sensor, it then injects to all 6 to keep the engine going. This motor does not use wasted spark though, it has the older system of a distributor/plug wires.

Demands for cleaner burning motors drove the need for more precise injection, and resulted [for example] in the modern diesel direct injection where the injectors fire multiple times on each firing stroke to better distribute the fuel to optimise performance/reduce pollution.
 

·
Registered
Joined
·
2,536 Posts
So the OP is correct that his 206 1.4 has two injectors operating simultaneosly, and the fuel from the injector close to the cylinder on the power stroke just hangs around till the next inlet valve opens?
 

·
Registered
Joined
·
2,536 Posts
crank sensor rings often have cut outs so the ecu has a base line (say tdc piston one) for injector duty cycles to work from.
But it follows from that that the ECU still does not know whether the tdc of piston 1 represents an inlet stroke or a power stroke. The only way an ECU can be aware of that is from a camshaft position sensor, because camshaft position determines which stroke is which.
 

·
Registered
Joined
·
36 Posts
But it follows from that that the ECU still does not know whether the tdc of piston 1 represents an inlet stroke or a power stroke. The only way an ECU can be aware of that is from a camshaft position sensor, because camshaft position determines which stroke is which.
Right, so his is a bit like single point it just sprays away, ether the intake charge is cramming up against a closed valve or flowing through an open one interesting!
 
1 - 12 of 12 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top