My question is, what does the knock sensor control? Would it cause an engine to lose substantial power after a few minutes of driving?

 

It detects cylinder knock (caused by detonation). Detonation can be caused by several factors; low octane fuel, too much spark advance, or a lean fuel mixture. The knock sensor will send a signal back to the PCM (power control module) to lower advance and/or enrichen the fuel mixture.

If you are suspect this is going on, have it checked ASAP, as valve and piston damage can happen.

Did you install a tuner recently?

 

No tuner intalled. Happened after my injectors failed and hydrolocked my engine.

 

Replaced my injectors and catalytic converters. The engine would run great for the first few minutes after starting it up in the morning, but would then seem to lose power after about 5 or 10 minutes.

 

When you start a car/truck, the knock sensor allows the PCM to adjust timing by sensing pinging or knock immediately. This allows the engine to get the most power out of the fuel you happen to be running. If the knock sensor malfunctions, the PCM just runs a default timing routine (like running 87). You would not notice the change, as it adjust to knock in fractions of a second. Because of the default program, some manufacturers won't flash the code for a bad knock sensor, but you will see it if you hook up a reader. Nissan does this. This is more noticeable in engines that specify 93 or above octane as there is a ton of power in those high compression engines. If you run 87 in those engines, sometimes the timing can't deal with the knocking alone. My Maxima knocked when I accidentally put in 87 and the engine could only reduce it, not eliminate it because of the high compression.

I hooked up my scanner to my Maxima once and it told me the knock sensor was bad. Once I replaced it, the power gain was huge. I was just used to driving so long in that default timing scheme. Nissan really should throw the CEL when those sensors go bad. Not sure if other manufacturers throw the CEL when their knock sensors go bad.

Your sensor could be in the middle of failing and what you are experiencing is the PCM switching between the default timing scheme and active (sensor working intermittently). They are easy to replace. The locations for them can be pretty bad though...

 

On my 05 5.4 they had to remove the intake to change the sensor.