I have an '03 SE, A/T with 157k miles. For the past 6 months, I've noticed quite a bit of knocking when accelerating, once the engine is warmed up. It is more noticeable at 40-45 mph (between 1800-2100 RPM). I have owned 4 cars with VQ35 engines ('02 Max, '07 G35, '08 G35, and this one) to know that they don't like anything lower than 91 octane, and they do let you know. In South Florida, premium fuel is 93 octane. So, that is all I use. I usually use Mobil or Chevron. I thought of changing brands and tried 2 or 3 tankfuls of other brands (BP, Marathon, and even Costco gas with their "5 times the EPA minimum required amount of fuel additives"). There was no change.

I have also noticed a decline on fuel economy. I used to get around 22-23 mpg of normal city/highway driving. Now, it won't go over 20 mpg, and my driving habits are the same.

She's burning a little bit of oil, which is typical with these engines, but I normally check and keep it topped off (every other week). So it is not oil starvation. There are no overheating issues either. I am thinking the knock sensor may be bad. However, the CEL is not on, and after scanning it, I've found no stored codes. In fact, there are no codes at all.

I've heard that knock sensors can go bad and not trigger the CEL, but there should be a stored P0325 or P0327 code.

Now right to the questions:

-Can a knock sensor be bad and not trigger the CEL or throw any codes?

-What kind of damage (whether short or long term) can knocking do to an engine?

Any kind of advice will be greatly appreciated. I don't know how bad engine knocking can be, but I do know it can't be good...

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Knock sensor failure will not trigger SES light but will store an error code. OBD scan tool with live feed will show as pending error code. I believe you need to install a pcv oil catch can to prevent blowby oil contaminating the intake manifold and throttle assembly lowering gasoline octane in the combustion area causing pinging and knocking.VQ35DE has a tapered piston combined with high compression will cause the escape of oil to the secondary piston ring. With that mileage its ideal to replace the knock sensor with OEM Genuine Nissan parts.

 

Please excuse my ignorance, but what is an oil catch can? I've seen this term a lot but I've never known what it is. Thanks.

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I used this kind of catch can.
http://www.ebay.com/itm/ADD-W1-Polish-Baffled-Universal-Aluminum-Oil-Catch-Can-Reservoir-Tank-Ver-1-/111361029651?pt=Motors_Car_Truck_Parts_Accessories&hash=item19eda27613&vxp=mtr
Near the firewall: look for the PCV valve: used 3/8 PCV tubing (not fuel or transmission tubing). Connect one end of the tubing to the PCV valve and the other end to the IN of the oil catch can. Connect another 3/8 tubing to the out of the oil catch can and the other end to the intake manifold.

Read this
http://www.nicoclub.com/archives/max...oil-catch.html
When was the last time you replaced the sparkplug?

 

This could be a sign that one or more of your ignition coils is going bad. What sucks is that its not enough for the ECU to tell you which one(s)....yet. The rear coils (1,3,5) tend to go bad before the fronts due to lack of ventilation in the back of the engine. It could also be a bad MAF.

Have you given your car a proper tuneup? The spark plugs last for 100K miles. You can replace them with OEM NGK platinums for another 100K miles, or go with the much cheaper NGK coppers, but they'll only last about 30K miles. Your fuel injectors may also need cleaning. TC-W3 IMO is the best, least harmful way (no harsh, alcohol like abrasives) of cleaning your fuel system(pump and injectors.) A couple of ounces per full tank. After about 3 tanks you should notice your car running better. Read about it on this thread here;

http://forums.maxima.org/fluids-lubr...itive-new.html

Assuming all other maintenance has been done, replace your primary, upstream O2 sensors. They get tired and do not throw an engine code. When they get tired you lose power and fuel economy.

Watch that oil consumption. 02 and 03 maximas are somewhat known to lose their engines due to pre-cat failures. Look up several threads here on the 5th gen forum. As a preventative measure, you can install a Y-pipe and delete the pre-cats.

If you have no stored codes, the KS is fine.


When a KS is bad, it will not turn on the CEL, but it will store the code. So your OBDII scanner will pick it up. That's why it's called a ghost code.

Knocking can do damage, but when your car is working properly, you should not hear any knock, or if you do, only briefly. Take my car for example. I had a KS ghost code for around 6 months. I knew it and waited till I could get some time to tackle the KS job. My KS was bad and the ECU stored the ghost code. In that state the ECU automatically adjusts the fuel map to prevent any knock whatsoever. In other words, knowing that the KS is bad, the ECU assumes 87 octane is in your tank, no matter what type of fuel is in your tank. I never heard any knock or heard it only briefly sometimes while the kS was bad.


I would get some used OEM coils from the junkyard and replace 1 by 1 until your car acts normal again. Also get a used MAF from the j/y.

Hope this helps.

 

If the knock sensor was bad you would be in safe mode. There's nothing wrong with the knock sensor.

I vote maf or O2s. It's an AFR issue b/c it doesn't do it when cold, since the ECU pumps out more fuel.
That RPM range is a common problem for pinging a little, but is usually resolved with 93 (so you must be running lean).

 

colt149 said: When was the last time you replaced the sparkplug?[/QUOTE] August 2013, around 10k miles ago. NGK Platinum spark plugs used. I had a code for the #4 coil, and I had it replaced with an OEM one.

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You can easily check if you need a catch can. Pull out the the tubing of pcv valve, the end tubing attached to the intake manifold. If the tubing are coated with oil ,that is the source of knocking. . Ignition coil failure, Maf sensor failure, O2 sensor failure will give error code and will trigger SES light. In the future, I highly recommend to replace your flexible pipe with Y pipe, gut the two precat not delete means removal of the mesh inside , so it will be free flow and install nonfouler to the two secondary O2 sensor. Just retain the main or rear catalytic converter.
Read this
http://www.energeticforum.com/renewa...n-foulers.html

In the meantime : install an oil catcher
hook up the engine to OBD Scan tool, Check for error code
Check your air filter: I recommend K&N filter and convert your OEM airbox to ghetto airbox. Drill 4 holes
1 inch diameter on the top of the removable holder of the airfilter.
Use a high octane gasoline
Perform the throttle relearn procedure

 

I just noticed something new that may narrow down the possibilities. It has been raining a lot in South Florida lately, and I noticed that when it is, there is no knocking at all! I thought that because of tire noise riding on a wet road, I couldn't hear it. So I went to a long road that has a long wall along it, so I can hear all the car noises better while driving. I waited when there was no traffic and drove at the speed the knocking usually happens with the windows down. The engine purred along like a cat, and no knocking. Now, you guys have given me a lot of possibilities that can cause knocking, from oil in the PCV valve line, to the MAF, and O2 sensor, and I really appreciate all your input. The question is what of all those possibilities could be affected (positively) by high levels of humidity in the air? Or is it maybe the mere fact that when it rains, the temperature drops enough for the engine to run cooler? Or maybe I'm just full of crap, and I still need to look at all those things... As I said before, I'm just trying to narrow down the possibilities is all. Thanks.
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Your ground points must be corroded. Because you can't tell which one is most affecting the car's running, just clean them all. Any wire connecting to the body or engine or tranny is a ground point. The simplest way to clean them is to unscrew the connector then screw them back in again, or unplug and re-plug a connector. You can be more throrough by polishing the metal contacts till they are shiny etc. Up to you.