Zack342

iTrader: (89)

oh since my recent dyno i have been trying to figure out why my engine is a bit down on power. in trying to figure out why some have suggest that it could be the knock sensor which would maybe explain why the car is about 10hp shy of what it should be doing. my best run was 160hp and 181Tq. the car is a 1999 SE-L CA spec. i was hoping it was a simple bad knock sensor so i decided to go to AUTOZONE again today and have the codes read of the ECU since i know that the 0304 is a ghost code. so the guy read the ECU and nothing no codes i was dissappointed but this leads to my question. if the knock sensor needs to be replaced then it would trigger a code which should be read by the ECU right?

if i read the ecu and there are no 0304 code does this mean the KNOCK SENSOR IS FINE? could bad plugs and fuel filter and dirty throttle body rob 10HP or so?. there are no codes in the ECU. no 02 sensors or knock sensor. also the gas mileage is ok, as well as throttle response.

here is my eariler thread http://forums.maxima.org/showthread.php?t=305422

DAVE Sz

iTrader: (2)

It may still be bad. Before it goes completely POS it works intetmittently. Disconnect the harness from it, reset the ECU and drive a few miles. It could be the O2 sensors, EGR maybe.

Zack342

iTrader: (89)

you wouldn't happen to have a pic of the harness which needs to be disconnect do you? also i can't manually reset the ecu from the screw since the 99's don't use a flathead screw driver. but this is possible though. that the knock sensor can be bad yet not trigger the light and at the same time affect perfromance at the same time allow the car to behave close to normal. i can notice some diffrence in acceleration. the car is still quick but it doesn't chirp the tires on 1st to 2nd like it did when it was totally stock. i am thinking the y pipe may have adversly affected the performance some how. the car ran better before i put on the y pipe. i had replaced the rear 02 sensor the week before due to 0901 code. well i bought the knock sensor off of ebay and its going on when my mechanic does my tune up. i am just trying to isolate wat the problem could be for my own piece of mind. car idles smooth., leaks no fluids and i use 93 octane abd synthetic. but i know its missing power for what's on there. http://forums.maxima.org/showthread.php?t=302270
that guy dyned 18 more hp and 10 more tq than me with almost the smae mods. if its not the knock sensor that is bad can need fore tune up result in almost 15 hp loss? i am confused and lost

95stillenmax

iTrader: (11)

its allways good to have a extra knock sensor buy a new one anyway its gonna go bad sometime anyway well thats what I would do

Zack342

iTrader: (89)

true but i wish i knew what was wrong with my car and why its making sure awful #s. i have been trying to figure this out since saturday but, i can't come to any difinitive explaination as to why it is the way it is. its not like it shudders, or surges or has a looping idle. normal operations is quite good. accelerations is good. i mean the torque is there 181 isn't too bad. should be more but it is obvious something is wrong as one can tell from the dyno which looks like the a nice mountain range. and all 3 dyno graphs yielded diffrent #s overall so maybe its an ignition or timing thing? but then there are no misfireing codes and i would told i would be able to feel a "bad coilpack". i have to wait until my mechanic gets back in mid may for my tune up untill then i will see if anyone has any ideas .

i just wish someone had a dyno of a car with a bad knock sensor for comparasion. so i can see what it looks like when the car retards the timing. the dyno starts off pretty good then about 3500rpm it starts getting all flocked up.

DAVE Sz

iTrader: (2)

I can get a pic tomorrow. But try this, when you look at the engine there is a valley under the intake runners and over the heads. From that valley comes out one batch or wire. At one end of that wire, inside the valley, you can't reach whilw the other is a black connector that is close to a smaller green connector. The black connector is the KS wire, trace and make sure it's right.

Max-2-GTR

Does that mean that if the ks is bad, the CEL won't turn on? If that is so, I'm gonna check my ecu cause my max seems to have lost power also.

Zack342

iTrader: (89)

well according to what i have learned it could be any # of reason why your car has lost power, KS, plugs, airfilter, fuel filter, a bunch of stuff

Max-2-GTR

Well, I changed my plug not to long ago...I've just cleaned the air filter.....the fuel filter, does the guy at the garage change it at every oil change?

Zack342

iTrader: (89)

fuel filters should be replaced every 15,000 miles or so.
They have a MUCH higher resistance than that. Mine measured 0.550 MEGA Ohms, which is 550,000 ohms.

The old one had a similar resistance, but was obviously bad.... since the installation of the new one GREATLY improved power output. According to the Haynes manual, they provide an AC output, which will change with engine knock... so they are tough to diagnose in a 'static' state.

Without a reader that can measure its output while the car is in operation, diagnosing a bad knock sensor is pretty much a 'crap shoot'.

Mine threw NO codes and still measured around the right resistance, but was still bad. Go Figure...

Also be sure to check the condition of the wiring leading to the KS. Check for continuity with a meter (to make sure the wires are connecting) to be sure there's no problem there.

Here's the rundown of my install from a previous post...

I just replaced mine... and D*MN, what a difference!

The fuel mileage had suddenly fell off a few mpg, and the power was feeling a little soggy.... Plus, there was a little hesitation just over 2k rpm.

Now, the part throttle low end and midrange feels like a totally different car! I can't believe the difference. It runs WAY better all the way across the rpm range!

One trick I've heard is to mount the knock sensor to the firewall, where it won't feel any 'knock' and will never retard any timing. This would work great as long as premium fuel is used..... and is what I would probably do if I raced this car a lot.

Just a thought.

Oh, I purchased mine on ebay for $90 'buy it now' and $1 shipping.

It was removed/installed with a 1/4" drive 12mm socket and a good swivel.... and a long extension. My wife's small hands came in handy with the initial installation of the new unit. I then tightened it down.

BTW, my car's check engine light was not on, and it showed no codes. The fuel mileage and power just fell off.... and it had a bit of a hesitation, which led me to believe it was bad. If your car suffers from these symptoms, GET A NEW KNOCK SENSOR!

Good Luck!


this is what i found in another post from n2omike

i am going to go with me having a bad knock sensor even though there are no codes in the ECU but it is missing power so this is my lats hope to redemption

maximka

what is fuel filter? where is it located? is it hard to replace?

nismo_SHA

i have a bad knock sensor any descirptions on how to fix is this a job not suitable for an amateur? how much does it $$$ to take it to the shop

Zack342

iTrader: (89)

this may help you a bit more than it helped me, your car is a 96 unfortuneately i have a 99 http://www.motorvate.ca/mvp.php/507

catalinoiu

http://vbxmaxima.8m.com/fuelfilter.html