Starting about a week ago, my car has been sluggish accelerating through about 2k RPM. Sometimes it seems as if it is hesitating and then the engine will catch and it accelerates normally. Then, the car stalled (it's an auto) 3 times, all while stopped at lights. The car stared back up easily each time. I did some searching and it seems like this could be caused by a number of things, among them, a faulty knock sensor, clogged fuel filter or a bad coil. I pulled code 0304 today, which is the knock sensor. I checked the resistence on the knock sensor (following the Haynes Manual instructions) and got infinite resistance, i.e. the sensor is bad.

So, from what I have read, a bad knock sensor can certainly cause sluggish or hesitant acceleration, but will it cause the car to stall as mine did on three seperate occasions? Is there a larger problem here, or will replacing the knock sensor fix the stalling?

Also, will driving 2000 miles on a bad sensor affect anything other than gas mileage? I would prefer to replace it when I am home from school, but if I am going to damage the engine by not replacing it, then I'll do it ASAP.

It's a 96 GXE with 108K miles on it.

 

A knock sensor that doesn't work will do nothing to your timing or engine performance. It will also allow your car to ping & knock, which isn't good.

An overactive knock sensor will pull your timing back to much and cause a decrease in performance.

A working KS should read almost infinite resistance. You need a good quality Ohm meter capable of reading more then 10Meg Ohms to correctly test it.

The KS works by producing AC voltage which increases with the severity of the knock. If the KS isn't working, no AC voltage will be produced thus nothing will happen to your car's timing. You ECU will think "all is ok". The 0304 code is generated when the AC voltage is out of the acceptable range, that means something is telling the ECU the car has to much knock. Now you either have something going on in your engine thats causing it, or your KS is a becoming a bit to overactive.

According to the Nissan Factory Service Manual (thanks Sprint) a dead knock sensor will never throw an error code. This can be bad as well, because now your car's timing may be to far advanced which can cause ping and knock. That will also hurt performance as well as your engine.

Bottom line, if your only getting 0304, just make sure your engine is running correctly before you change that sensor. If everything else checks out OK, you may have an overactive sensor.

 

i've gotta question to add on this topic. about how much should one cost? courtesy has a knock sensor "kit" for $157. is that decent priced?

 

A bad knock sensor won't cause stalling. It is more likely a dirty throttle body, dirty IACV, or idle set too low. Like njmaxseltd said, be sure you eliminate all other symptoms before springing for a KS. Other problems that cause the engine to run rough could trigger an overative KS into thinking the engine is pinging, which reduces timing even if not needed and can lead to 'surging' acceleration. A new KS can be had for around $110 or so if you shop around.

 

I've suspected an overactive knock sensor on my car for a while as a cause of the low power and surging power curve. As I accellerate up a slight incline at a constant rate I can feel the power coming on in waves. What's an easy test? If I just unplug the damn thing when I drive home today and the car drives at full power without surging (watching out for the pinging, of course) then that should be a slam dunk, yeah?

 

A non functioning knock sensor will not "do nothing" to you timing and engine performance. When your ECU detects a non functioning knock sensor, it defaults your ignition timing to a safe mode table that is based on low octane gas. (to save your engine from any possibility of a recurring knock) So a non functioning knock sensor will retard your timing and cause slugishness and hesitation.