Quote:
Originally Posted by Lizard29
Check to see if you have a damaged Knock sensor
this is what happened to my car & once replaced, was running fine
it not only effected acceleration, but also engine timing etc.
|
Wrong. What you experienced is actually a symptom of a symptom, and replacing the knock sensor probably didn't fix anything. It just put a temporary band-aid on it and hid the actual problem. The knock sensor doesn't constantly affect engine timing. It only tells the ECU that it needs to retard the timing a certain number of degrees when you get spark knock/pinging. If the knock sensor was damaged and was constantly sending a signal, the ECU would still only retard the timing to a certain point, and your engine should have still run decently. Not at 100% performance/efficiency, but still decently.
This is gonna be a long post, but bear with me if you want to learn about what the knock sensor is actually for. Note that it IS possible that a damaged knock sensor was the sole reason for your problem, but the chances of this are extremely low due to the design of our ECUs. And keep in mind that I'm not a Corolla guru, but the following principles have nothing to do with Corollas specifically; they apply for ALL engines that are computer controlled.
Retarding the timing will actually make your engine run worse unless it was already advanced too far to begin with. From factory timing, retarding the timing a couple degrees will make the ECU run the engine slightly richer (more fuel) while advancing the timing a couple degrees will make the ECU run the engine slightly leaner (more air.) A richer mixture will be more prone to flooding and sputtering because the injectors are dumping way too much fuel into the cylinders, as well as raising the flashpoint of the mixture slightly. A lean mixture will be more prone to early detonation because of the higher air/fuel ratio, which lowers the flashpoint of the mixture. Your engine can also ping if it's simply running too hot, which will cause a correct air/fuel mixture to detonate early. This is called pre-ignition, and if your engine has ever overheated and 'dieseled-out' when you turned it off, you experienced pre-ignition from the heat.
Technically, if it was timed perfectly, and the igntion and fuel systems were both in good order, the engine should have run at it's best performance with the knock sensor dead or unplugged at acceleration/WOT. The drawback might be a little bit of pinging/spark knock, which would mean that the engine is running slightly lean. This could be normal. Many modern engines that are controlled by an ECU are timed slightly lean from the factory to increase fuel mileage. Not enough that detonation or pre-ignition occurs frequently and damages the engine, but enough to save a couple mpg at high RPM. The knock sensor is only there as a contingency, in case it DOES ping.
If unplugging the knock sensor magically makes your engine run worse, there are a few things you should check. First, try replacing your plugs, wires, distributor cap, and rotor. Worn ignition components can cause pinging/spark knock. Going to NGK spark plugs that are one step colder can also help in extreme cases. NGK has a diagram on their site that explains this, if you cant find it just Google 'spark plug temp.' We try the ignition system first because it's usually the cheapest possibility.
If replacing the ignition components doesn't make the engine run better without the knock sensor plugged in, the next step is your fuel system. Your fuel pump may be dying, causing fuel PSI to go down, which in turn causes your injectors to move less volume, which in turn causes the engine to run lean and ping. Another possibility is a plugged fuel line or filter. This will actually increase PSI in the line, but the pressure will be regulated at the Fuel Pressure Regulator on the fuel rail, and as a result, the volume of fuel moved will again drop sharply, again resulting in a lean condition.
If checking those components doesn't solve anything you'd better check your timing. It could be advanced a few degrees too far. From factory timing, this could be caused by the timing belt slipping a tooth or two (happens frequently) or a fouled/dead Crank Position Sensor (much less frequently, but also possible.)
And finally, if all else fails, it's possible that your ECU is on it's way out the door. It DOES control the timing, after all.
EDIT: By the way... If it is running rich with the knock sensor unplugged, it means that your timing was retarded a little too far to begin with, or you're getting too much fuel to the cylinders. As a result, the knock sensor told the ECU to compensate for it. Again, this is not an ideal condition. The ECU should never be compensating for incorrect timing or fuel delivery.
Linear Mode
