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Knock Sensor Replacement
 
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Pelican Technical Article:

Knock Sensor Replacement

Steve Vernon

Time:

1-4 hours

Tab:

$25 to $90

Talent:

****

Tools:

13mm wrench or socket, flathead screwdriver

Applicable Models:

Porsche 944 Turbo (1986-89)

Parts Required:

New knock sensor

Hot Tip:

Get ready for a long day if the idle speed adjuster is in the way

Performance Gain:

Piece of mind on engine knock

There is one knock sensor on the early 944s. This knock sensor plays an important role in the engine management system. The sensor detects knock or ping in the motor, which is pre-detonation. Pre-detonation can cause serious and expensive damage to the motor. 

The sensor is located between the number two and three intake runners. While it is packed in tight behind the idle speed adjuster, it can be replaced as long as you can access the single bolt holding it in place. If your idle speed adjuster is mounted in a way that it blocks getting a socket on the sensor, you will need to remove the intake manifold to move the idle speed adjuster and change the knock sensor. That was the case with our project car. If it is the case with you, please see our article on intake manifold removal.

The knock sensor is located down between the number two and three intake runners (red arrow).
Figure 1

The knock sensor is located down between the number two and three intake runners (red arrow). You will need to remove the plug wire for the number three spark plug.

With the plug wire removed, you can see the single 13mm bolt holding the knock sensor in place (red arrow).
Figure 2

With the plug wire removed, you can see the single 13mm bolt holding the knock sensor in place (red arrow). Note: the fuel injectors and fuel rail have been removed for photographic purposes.

If you can get a 13mm socket to sit flush on the sensor bolt, you can simply remove the bolt and sensor, disconnect the wiring and install a new sensor (red arrow).
Figure 3

If you can get a 13mm socket to sit flush on the sensor bolt, you can simply remove the bolt and sensor, disconnect the wiring and install a new sensor (red arrow).

On our project car one of the mounting bolts (red arrow) for the idle speed adjuster was blocking access to the sensor bolt.
Figure 4

On our project car one of the mounting bolts (red arrow) for the idle speed adjuster was blocking access to the sensor bolt. No matter what angle we came at it from there was no way to remove the bolt and sensor. Unfortunately, this turned a simple and quick job into a much longer one, as we had to remove the fuel rail, injectors and intake manifold. If this is the case with your car, please see our articles on those procedures for additional assistance.

With the manifold off I could remove the 6mm Allen bolt (red arrow) holding the idle speed adjuster out of the way.
Figure 5

With the manifold off I could remove the 6mm Allen bolt (red arrow) holding the idle speed adjuster out of the way. I then used a 13mm socket to remove the knock sensor (yellow arrow).

Separate the wiring connection from the sensor by releasing the wire clip and pulling them apart (red arrow).
Figure 6

Separate the wiring connection from the sensor by releasing the wire clip and pulling them apart (red arrow).

Use care when releasing the clip (red arrow).
Figure 7

Use care when releasing the clip (red arrow). As these clips get old and go through heat cycles, they can get very brittle. Installation is the reverse of removal.


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