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Knock Sensor FAQ & Replacement
Author : Ken Rosengren
Published : 11/23/02
Last Modified : 11/23/02
How-to: Knock Sensor Replacement on a VE30DE (92-94 MaximaSE)


Q) What does a knock sensor do?

A) A knock sensor is a specially designed listening device for car engines. It listens for engine knock, or detonation (pinging). Detonation can be very bad for an engine and is the result of the fuel/air mixture exploding too quickly instead of burning evenly and rapidly. This is due to either bad fuel, ignition timing which is too high, or built up carbon deposits in the engine (which increases the compression ratio). The sensor is small and consists of a piezoelectric sensor that listens for knock by detecting pressure. It is very sensitive and can be considered worthless if dropped. The vibrational pressure is then converted into a voltage and sent to the ECU for evaluation.

Q) How do I know if my knock sensor is bad?

A) Symptoms of a bad knock sensor include a sluggish engine, poor acceleration and poor fuel economy. Knock sensors rarely fail outright and more often get “soft” over time and cause false signals to be sent to the ECU, which thinks the engine is knocking when it’s really not. Thus, the ECU will reduce the ignition timing to the engine. The knock sensor on the VE30DE is prone to corrosion of the terminals and harness connection. This is due to the harness weather seal getting brittle and cracking, allowing moisture to seep into the harness from the rear and corrode the terminals. This creates a poor connection and faulty voltage readings to the ECU.

Q) How do I test my knock sensor?

A) The knock sensor voltage can be checked through an electrical harness located right above the thermostat housing (where the lower radiator coolant hose attaches to the engine). It is a gray connector with an orangish red cap with two wires. Unplug the connector and attach a multimeter (or voltmeter) to the lower harness (the male connector). The wire for this connector should go left and underneath the intake manifold. Check the front most terminal (see pic) and ground out the negative point. You must have a multimeter than can measure more than 10 M ohms. Continuity should exist. This method is per the Factory Service Manual. NOTE: Knock sensors should be considered regular maintenance items. If you have over 100K miles and have never replaced the knock sensor, you can probably consider it bad.

Q) What parts will I need?

A) For knock sensor replacement only, here are the required parts:

-Normal hand tools (8, 10, 12mm sockets, long extensions, 14mm open-end wrench, large adjustable wrench, torque wrench, Philips screwdriver, 6mm hex key socket (I THINK this is right, check the size of the intake plenum hex bolts first to see if it fits before you start)).

-Coolant and distilled water (about a gallon total)

-Knock sensor PN 22060-30P00

-Knock sensor sub harness PN 24078-30P00

-Throttle body gasket PN 16175-53J00

-Intake plenum gasket PN 14032-97E00

-2 Intake manifold gaskets PN 14035-97E00

-Liquid gasket which is impervious to coolant (high-temp)

Q) What are some other things I could do while I’m in there?

A) Since you will be draining some coolant and releasing the fuel pressure, here are some things you should think about doing (though not required):

-Replace all fuel lines with rubber fuel injection hose (don’t get normal fuel line since they are not reinforced for high-pressure fuel injection systems).

-Replace all coolant hoses (radiator hoses, bypass hoses, throttle body hoses, there are a lot of small ones that are very difficult to get to normally, this is your chance to do it easily)

-New vacuum hoses (you’ll need at least 8 ft I believe, there are a lot of small ones)

-Fuel injectors: Might want to get them cleaned and install new o-rings and grommets

-Fuel filter, since the fuel pressure is released, why not?

-Port match intake manifold/plenum and throttle body

-New coolant temp sensor

-New PCV valve

-New thermostat

Q) I’ve never done major work on a car. Can I do this successfully?

A) Replacing a knock sensor isn’t necessarily hard work, but it is time-consuming. As long as you think the project over beforehand and label everything you disassemble, you should go fine. The worst thing that can happen is you end up with a loose hose somewhere or have an intake or coolant leak.

Now the fun part, actually doing the job! These procedures were produced from my 93 SE 5spd. If you have an auto, you might not have as many vacuum lines to disconnect since the 5spds have the power valve and purge canister.

Release fuel pressure

The FSM states that to release the fuel pressure, you need to remove the fuel pump fuse located in the interior of the car under the panel by your left knee when you’re sitting in the driver’s seat. Crank the engine up, let it die, then crank it a few more times until it doesn’t start. Then take out the key and replace the fuse.

Drain coolant

On the bottom right side of the radiator is the drain cock (plastic t-handle with a small clear rubber hose hanging down). Open the drain cock and allow about 3-4 quarts of coolant out. You don’t need to drain the entire engine since the intake manifold only holds a small amount of coolant, and this is the first part to drain since it’s highest on the engine. Remember to shut the drain cock!

Disconnect battery

Very important! You will have open fuel lines, so one spark could start a fire! Remember to disconnect the negative cable first.

Disconnect intake and air box

-Unclamp the 4 latches on the air box as if you were changing your air filter

-Loosen the throttle body air intake tube clamp

-Unclamp the two big rubber breather hose attached to the plastic air intake tube.

-Unhook the two vacuum lines attached to the resonator, then lift the entire air intake unit out and out of the way

Disconnect blow-by tube

This is the small, long metal tube attached to the front of the intake plenum

-Unbolt two 10mm bolts and two rubber hoses.

-Carefully unhook the wiring harness clamps. These are very brittle and if not already broken, will break if you force them! Have some zip ties ready if you do break them

Throttle Body

Just disconnecting the throttle body is the easiest way to do this. You can leave the TB attached but then you must remove many vacuum and coolant lines from it. It’s easiest just to remove it and lay it on the side.

-Remove the throttle and cruise control cables by loosening the left nut with your 14mm open-end wrench (furthest from throttle body, if you loosen the right nut you can change the tension on the cable, not good!). Then remove the cable from the TB bracket.

-Remove a short vacuum hose on the bottom of the TB that connects to the intake plenum

-Remove the 4 hex bolts using a criss-cross pattern and remove the TB

-For added stretch you might have to unclip the TPS harness from its mount

Intake Plenum

-Unplug and remove the three rear coil packs

-Remove three ground straps (10mm bolts) 2 on front of plenum, one on left side *Take a dremel or steel wool or something and clean these ground straps and mounts to get the oxidation off, these need to make good grounds!*

-Remove the vacuum hose from the power valve on the left side of the plenum (N/A for auto)

-Remove the tiny cruise control vacuum hose from the rear of the plenum

-Remove the mid-size vacuum hose on the rear of the plenum that routes to the brake booster

-Remove the mid-size vacuum hose right underneath that (this one meets a metal pipe which eventually winds up at the PCV valve.

-Now, remove the two 12mm bolts that this PCV metal pipe connects to the plenum with

-While you’re down there, remove the two 12mm top bolts of each plenum stiffening plate (only one plate is shown in the picture, there is another to the right by the EGR)

-Take your big adjustable wrench and crack the big nut loose on the EGR valve. Loosen it all the way until it moves freely and you can see a gap between the EGR valve and metal EGR tube

-Remove the 4 remaining vacuum lines by the throttle body location.

-This one’s hard to see, but there are 4 12mm bolts holding on the EGRC valve on the lower right side of the plenum. Two on the right side, two on the back side (one is not visible in the pic)

-Remove the 10mm bolt holding on a metal vacuum line mount on the right side of the plenum, in front of the throttle body. It has a yellow sticker on the mount.

-Now all you have to do is crack loose the 6 hex nuts in a criss-cross pattern and pull off the plenum! If it doesn’t come off freely, hit the “Nissan” part lightly with the palm of your hand. Now, when removing the plenum, make sure everything is disconnected before you rip something off

Fuel Rails

-Loosen the screw clamps for each of the 4 small fuel lines (2 on each rail)

-Remove the fuel “T” line on the left side by removing the two 10mm bolts. Be careful not to drop these down the intake manifold as you’ll have to fish it out of the intake port of the head if you do (speaking from experience here)

-Break loose the fuel lines and be prepared for some fuel to spill out. Have rags handy. Remove the fuel “T”

-Now remove the 4 hex bolts of the fuel rails. Be prepared to gather a plastic spacer and metal washer for each bolt as they will fall and get lost easily. Remember how they fit! Plastic washer on bottom, then fuel rail, then metal washer on top, then bolt.

-Lightly pull up on the rails, when they are loose you can remove the right fuel lines. Do not drop the fuel rails, injectors are fragile and expensive!

-Watch for any loose fuel injector grommets (where the fuel injectors sit in on the manifold). Don’t lose these unless you have new ones ready to go.

Intake Manifold

-Remove the left radiator hose and the smaller bypass hose right next to it. You only have to disconnect them from where they meet the manifold

-On the right side, remove the three bolts that hold on the coolant tubes to the right side of the manifold. You may have to pry a bit to get this off as it’s sealed on with liquid gasket.

-Disconnect the coolant temp sensors (big one and small one, be careful as these electrical connectors are brittle, and you’ll have to pry the small metal wire clip to remove it)

-Now crack loose the 4 nuts (not bolts yet!) in a criss-cross pattern, 2 on each side of the manifold

-Now loosen the 6 hex bolts, again in a criss-cross pattern (important, you don’t want to warp the manifold by improper untorquing)

-Make sure you gather the washers that go with the nuts

-Pop off the manifold (you might have to pry a bit)

Water Pipe

By now, you can see the knock sensor and the pile of crud in the valley of your engine, but there’s no way to break the sensor bolt loose because the water pipe is in the way!

-Remove the two nuts and washers on the left side (connecting to the water pump)

-Remove the two bolts that bolt vertically down into the engine block on the right side.

-Now, using a LARGE flathead screwdriver, pry the water pipe off the studs on the water pump side and you’ll be able to hold the water pipe up to get to the knock sensor. Much easier than removing the thermostat housing and all those coolant lines on the right side

Knock Sensor

Finally, one bolt and it’s off. Clean the contact point thoroughly since any dirt or gunk will make the sensor less effective. Now, put the new sensor in and BE CAREFUL with it. Remember not to drop it or hit it against anything. Even when bolting it down take extreme care, you do NOT want to over tighten it! I couldn’t find a torque figure in the FSM so I just tightened it down until I felt resistance and went about another half turn. My uncalibrated torque right arm says it was about 15-20 lb/ft.

Now it’s time to clan the gasket surfaces on the head, manifold, plenum and throttle body. Use a paint scraper for the best results. A bit a steel wool won’t hurt either. Make sure no debris or anything falls into the intake ports in the head. Also clean off the water pipe where it was sealed with liquid gasket

Installation is in the reverse order of removal. Use a solid bead of liquid gasket on all surfaces. Completely circle around all pipes (on the right side of the intake manifold, the coolant pipes that attach have two pipes. Make a circle around each hole so they don’t leak into each other). Don’t use TOO much liquid gasket though. A thin solid bead is all that is needed. Allow at least an hour for it to dry (by the time you get everything else back together, at least an hour will have passed)

Intake manifold torque for the hex bolts is 20 ft/pounds. For the 4 nuts it is 24 ft/pounds.

Again, torque them in a criss-cross pattern (middle bottom left, middle top right, middle bottom right, middle top left, far bottom left, etc)

Fuel rail bolt torque is 20 ft/lbs

Intake manifold hex bolt torque is 20 ft/lbs. Criss-cross pattern.

Throttle body torque is 15 ft/lbs, criss-cross pattern

Make sure you replace all the plastic spacers and washers correctly when you replace the fuel rails.

When replacing your coolant, fill it up to the top of the radiator cap. Now, carefully open the 10mm nut by the large coolant bypass hose on the right side of the intake manifold (by the two pipes and the coolant temp sensors). This is a purge valve and releases the air in the system as you fill it up.

Start it up and check for leaks. When all done, take it for an easy test drive quick around the block then check for leaks when you return. On the first real drive, drive slowly as if you were breaking the car in. The metal manifold gaskets need a complete heat cycle to seal correctly. You don’t want to risk doing this over again! Then disconnect the battery (negative first, then positive) and let it sit overnight. In the morning, enjoy your newfound VE power!

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