While driving the car runs fine, but when stoping at a stop it idles rough and try to cut off. pulled code gave code p0325. I changed the knock sensor but still gets code p0325, and car still misses at...
Hi Thomas,
We have a couple different issues here.
First, your Maxima is either NOT a 1995 model, or it is a very late 1995 model that "thinks" it's a 1996. The reason I say this is because a 1995 model Maxima is NOT OBD compatible and is not capable of outputting "P-codes" to a generic OBD scanner.
Those Nissans that were claimed to be OBD compatible in the late 1995 model year only output certain codes. To find out the rest of the story, you still need a scanner that has software capable of accessing the engine computer through the Nissan-2 connector (usually in the fuse block area).
Then you need to understand about Diagnostic Trouble Code (DTC) P0325.
This code does not necessarily mean that you need a new knock sensor. I think you will be a little less confused if you know the facts. What you need to know about ALL fault codes is that they NEVER tell you what parts to replace. Fault codes only tell you that the computer has a problem with one of the many circuits and systems that it monitors. The fault code will tell you which system is failing or which circuit is failing. They DO NOT tell you what is wrong with the circuit or system that it is reporting. The person diagnosing the vehicle is supposed to figure that one out.
Most people think that "diagnostics" means plug in the "magic box" and replace everything the computer tells you to replace. I WISH it was that easy!
Now that you know all of this, we can examine the code itself. What causes this code to set? ...I'm glad you asked. The computer controls the ignition timing in your car. The trick is to advance the timing as far as possible (for more power and efficiency) while not advancing it too far, which will cause pre-detonation (also known as "ignition ping"). Pre-detonation can cause serious engine damage, including burning holes through a piston.
Here is where the knock sensor comes in.
SCENARIO 1: The computer advances the ignition until the knock sensor "hears" an ignition ping. When this happens, the knock sensor sends a signal to the PCM to let it know that the engine is "knocking". So the computer responds by retarding the timing a little to stop the knock. When the knock stops, the knock sensor will stop sending a knock signal to the computer.
DTC P0325 sets when the computer has ******** the ignition timing as far as it possibly can and the knock sensor is STILL sending a knock signal.
SCENARIO 2: The computer also tests the knock sensor by deliberately advancing the timing too far for a few seconds to see if it gets a signal from the knock sensor.
So, P0325 can also set if there is NO signal from the knock sensor when the computer is EXPECTING a signal.
For scenario 1, the cause is usually a mechanical knock in the engine. Loose timing belts, worn/loose timing chains worn distributor shafts, bad pulley bearings, etc. The knock sensor does not know the difference between a knock caused by pre-detonation and a knock caused by a loose valve lifter (or other mechanical reason). The knock does not go away when the timing is ******** because the knock is not CAUSED by timing....code P0325 sets.
For scenario 2, the cause is usually either the knock sensor itself or a problem with the wire between the knock sensor and the computer or the knock sensor is not grounded properly. These things will cause the knock sensor to not be able to get a message through to the computer....code P0325 sets.
Now, the misfire at idle is a whole other issue. The computer will default to base ignition timing settings if there is a knock sensor fault. You may notice a little loss of performance, particularly during heavy acceleration, but there is NO WAY that your knock sensor is the CAUSE of ANY misfire - especially not at idle. However, it is VERY possible that whatever is causing the misfire could also be the cause of the knock sensor code.
Basically what I am saying here is that you need to put the knock sensor problem "on the back burner" until you find out what is causing your misfire. Unfortunately, misfires can be cause by a LOT of different things ranging from a bad spark plug to a cracked cylinder head or worn-out piston rings. The misfire simply has to be diagnosed using the proper procedures to avoid replacing a bunch of things that will not fix the problem.
With all that said, WHEW! I hope you got through all that!
The older Nissans are notorious for the distributor shaft bushing going bad and causing a loud "rattling" noise. The movement of the shaft can cause a cylinder misfire, and the rattling can cause a knock sensor code to set. I have fixed many of the Nissan V-6 engines with this same problem by replacing the distributor. This is the FIRST place I would look. If your distributor is not rattling, try revving the motor just a little and see if it rattles. If it does, replace it. If it does not, let me know and we will look elsewhere for the cause of your problem.
-Dave (dttech)
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