should I replace my knock sensor?

[cprince]

I bought an OBD II scan tool, and it said that my knock sensor is bad(no check engine light, though). From what I heard, if the knock sensor is bad, the car's computer will use the default timing. I the performance maybe a little bad, but it's still drivable. So, should I spent $138 for a knock sensor or wait another year(and hoping that the car still works) until the Chevy Camaro comes out? BTW, it's a '95 Altima with 65,000 miles on it.

 

[Homer Simpson]

if it truely is bad, i would replace it. without it, the car cant pull timing should you have detonation (say from a bad tank of gas). detonation or knock can lead to a blown head gasket if its severe enough. however, im not familiar with an altima and do not know how low the timing gets set too should the sensor fail. if its overly safe and fails over to very low timing, performance will suck as will gas mileage but you'd be safe. if it fails over to just base timing, you could risk the aforementioned knock problem.

 

[Vette73]

How did the scanner say it was bad? Is you engine light burned out? If not erase the stored code and drive to see if anything pops up.

 

[cprince]

Originally posted by: Marlin1975
How did the scanner say it was bad? Is you engine light burned out? If not erase the stored code and drive to see if anything pops up.

The code of the scanner was P0325. I did some research, and I found out that the knock sensor would not cause the check engine light to turn on.

 

[woodie1]

As mentioned above, clear the code, drive a few days and then check it again.

 

[Zenmervolt]

Originally posted by: Homer Simpson
if it truely is bad, i would replace it. without it, the car cant pull timing should you have detonation (say from a bad tank of gas). detonation or knock can lead to a blown head gasket if its severe enough. however, im not familiar with an altima and do not know how low the timing gets set too should the sensor fail. if its overly safe and fails over to very low timing, performance will suck as will gas mileage but you'd be safe. if it fails over to just base timing, you could risk the aforementioned knock problem.

Without it, the car will default to the most conservative pattern. That's a universal fail-safe.

Cars ran fine without knock sensors for decades, as long as he continues to use the required fuel grade specified in the manual, he'll be fine.

ZV

 

[jagec]

Originally posted by: Zenmervolt
Cars ran fine without knock sensors for decades, as long as he continues to use the required fuel grade specified in the manual, he'll be fine.

ZV

:thumbsup: No knock sensor in my car IIRC.

 

[DivideBYZero]

Three KS in my car . 🙂

 

[Minjin]

With a bad knock sensor, the car will feel like a dog and get poorer gas mileage than it should. I don't understand why its even a question.

 

[cprince]

Originally posted by: Minjin
With a bad knock sensor, the car will feel like a dog and get poorer gas mileage than it should. I don't understand why its even a question.

It's $138 that could go toward a new Chevy Camaro when it comes out.

 

[Zenmervolt]

Originally posted by: Minjin
With a bad knock sensor, the car will feel like a dog and get poorer gas mileage than it should. I don't understand why its even a question.

You've got to be kidding me... You know a lot about theory, and are clearly a very good wrench, but this is everyday use on a throw-away car, not a racetrack situation.

This is a '95 Altima. The 5 hp lost because the engine is running conservatively will not be missed. And the knock sensor's impact on fuel mileage is so small as to be effectively none. It's a smaller fuel mileage hit than running the A/C in the summer; it's just not worth caring about in actual practice.

OP, don't worry about it. Just use the required grade of gasoline and don't worry about it.

ZV

 

[Pacfanweb]

Just pointing out, is a 95 Altima even OBDII? That didn't start until 1996. I guess some makers could have started a year early, or your scanner scans the old stuff, too?

 

[cprince]

Originally posted by: Pacfanweb
Just pointing out, is a 95 Altima even OBDII? That didn't start until 1996. I guess some makers could have started a year early, or your scanner scans the old stuff, too?

It's OBDII. I guess Nissan put them in earlier than required. I wish I had bought a more sophisticated scanner with freeze frame and live data recording. It's only $149 at amazon.com. This one costs me $60 already. I might return it.

 

[Gamingphreek]

Originally posted by: Pacfanweb
Just pointing out, is a 95 Altima even OBDII? That didn't start until 1996. I guess some makers could have started a year early, or your scanner scans the old stuff, too?

They should be. My 1995 Toyota Tacoma is OBD II also. It does have another diagnostic port under the hood that, for the life of me, I can't figure out what it does.

 

[theeedude]

Get a used knock sensor from copartfinder
http://www.copartfinder.com/rap/requestMyParts.do
I used it and it was dirt cheap compared to getting new one.

 

[natto fire]

Kind of weird that it has a knock sensor with it's relatively tame compression ratio of 9.2:1, but I guess they must use some pretty aggressive ignition timing. As already stated, it will not be very noticeable running the more mild ignition maps, hence why the CEL is not thrown.