crankshaft-rotation-sensor.htm¶

1 excerpts.

Crankshaft Rotation Sensor¶

evilution.co.uk/mod/crankshaft-rotation-sensor.htm · p. 1 · Applies to: unknown

Mod Description The crankshaft is what the pistons are attached to. The crankshaft sensor measures the rotation of the crankshaft (and therefore the position of the pistons) so the ECU knows when to inject petrol and to fire the spark plug. Mod Details Premium Yes Difficulty Mod ID 888 Credit evilution For Link https://evilution.co.uk/mod/crankshaft-rotation-sensor.htm Copy to Clipboard Car Cuts Out When Hot The crankshaft rotation sensor plays an important role. It tells the ECU where the pistons are so the fuel is injected and the spark plugs fired at the correct time to create the correct 4 stroke combustion cycle. It is becoming more common now for these to fail, become intermittent or even for the fixing bolt to become loose. If it has failed, the car simply will not start. If the sensor has become water damaged it can cause intermittent starting and occasional stalling. If the sensor fixing bolt is loose, starting will also be intermittent, as will running. However, more often than not, you may find that the car runs really badly or stalls totally only when it has warmed up . These sensors can suffer from internal heat damage which increases the internal resistance. Sometimes the engine will only stall when the sensor is hot and the engine revs are low. Removing the sensor really is the only way to be sure. If the bolt isn’t tight when you try to remove it then try tightening it up. If the sensor drips water when you remove it and turn it upside down you should replace it (or perhaps dry it out and try to reseal it as a quick repair). If the sensor looks fine and the bolt was tight, replace it with a new one. Symptoms Poor running. Misfire. Stalling. Cutting out when warmed up. Not starting. Finding & Removing The Sensor Other sites will tell you to remove the top and bottom intercooler pipes, throttle body, intercooler fan and the intercooler just to get to the sensor! If you you aren’t totally ham-fisted you can save yourself a lot of time and messing about using 1 simple and cheap tool. Firstly, undo the clip holding the intercooler pipe to the throttle body. I have the Forge silicone hoses on mine but the method is the same. Loosen the pipe clip at the bottom of this pipe where it goes into the intercooler, this will allow you to swing the pipe out of the way. Disconnect the throttle body electrical connection, remove the 4x Torx “E” bolts and take the throttle body from the engine. (You could forego removing the top pipe clip totally if you loosen the lower pipe clip, remove the 4 torx bolts and swing the pipe up with the throttle body still attached. Disconnect the electrical connection though). How Can The ECU Time The Engine With Only 1 Sensor? This is a question that came to me a few years ago and it took me some time to work it out. Therefore, there must be at least 1 other person who is interested in knowing. The crankshaft has to rotate twice (720°) for a full combustion cycle, however, the cam shaft only has to rotate once (360°) The crankshaft has a clutch/flywheel with teeth all around except for 2 that have been removed. It’s the gap that the sensor sees as the crankshaft spins. That means the crankshaft sensor sees the gap pass twice during each full combustion cycle because the flywheel rotates twice. However, it only uses 1 of those to inject fuel and fire the spark plugs. But how does the car know which 1 of the 2 rotations it needs to use to do that? Imagine if it picked the wrong one, it’d be firing the spark plugs and the injectors in the wrong order. That wouldn’t work right? Wrong The engine fires the spark plugs for both rotations and initially it injects fuel for both rotations too. 1. The Spark (Wasted Spark) The ignition system is designed to fire the plugs on both the compression stroke and the exhaust stroke. On the compression stroke, the spark ignites the fuel. On the exhaust stroke, the spark fires into empty air (the “wasted” spark). Since it fires every time the piston reaches the top, the ECU doesn’t actually need to know which stroke it is on to get the engine to start and run. 2. The Fuel (Initial “Blind” Injection) This is where it gets interesting. To get the car started, the ECU initially operates in a “Batch Fire” mode. It sprays fuel into the intake ports based solely on the Crankshaft Position Sensor. It doesn’t know if the intake valve is open or closed for a specific cylinder yet. It just sprays, knowing that the fuel will “sit” behind the closed valve for a split second if it’s the wrong stroke, and then get sucked in when the valve finally opens. 3. Finding the “Phase” (Crankshaft Acceleration) Once the engine is actually rotating, the ECU uses a method called Segment Timing or Crankshaft Speed Fluctuation “sync up” for more precise fuel injection: When a cylinder is on a compression stroke, the starter motor (or the engine’s own momentum) has to work harder to push the piston against the air pressure. This causes a tiny, microscopic deceleration in the crankshaft speed. When it’s on an exhaust stroke, there is no pressure, so the crank doesn’t slow down as much. The ECU’ is fast and precise enough to measure these tiny differences in the “teeth” of the flywheel. Once it detects that specific “dip” in speed, it says, “Aha! That’s the compression stroke,” and it switches from “Batch Fire” to Sequential Injection for better fuel efficiency. Clever! Or lazy cost cutting. One of the two. It does mean is wastes a tiny amount of fuel and over-fuels the engine for a second. It also means that the engine can take more rotations to start unlike engines with a separate camshaft rotation sensor. On the flip side, it also means there’s less to go wrong and when you time the engine, the camshaft can be 180° out of phase from how it was and the engine will still run. Click if info helped 172 likes 115008 views Print