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Discussion Starter #1
There are two sensors on the Bentley Eight, one at the front next to the crank pulley/harmonic damper and the other right at the back underneath the gearbox housing (bell housing). The front sensor is for TDC (Top Dead Centre) so is used for determining when to fire the ignition. The rear sensor is an RPM/speed sensor.

Both types have the same part number (0261210047) which is a Bosch part. The good news is that you don't have to pay hundreds of pounds for it as there are aftermarket alternatives which are used on Alfa Romeo and Kia cars made by Intertronic etc. Just take your part to a local autofactors and they will cross match is for you, expect to pay around £70 for a new sensor. The old sensor is a metal housing but the new ones (which ARE compatible) come with a black plastic housing.

The sensor's job is to transmit a pulse to the ECU whenever an 'event' occurs. The pulse tells the ECU that the sensor has seen a certain position reached (be it on the flex plate or the crank pulley).

The job itself is not too difficult and should only take 30 minutes to an hour each if you're a novice. Step 1 to 12 are for the front sensor and step 13 onwards covers the rear.

Step 1 - Pull the bonnet release under the steering wheel and lift the bonnet


 

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Step 2 - Standing on the nearside (passenger side) you should look down past the air con compressor and behind the bottom pulleys to locate the sensor as shown





Step 3 - To improve access (you don't have to do this), I removed the air con belt, slacken off the large (8mm?) allen key bolt as shown in the first picture. Then the 17mm nut/bolt on the other side as shown in picture 2. When you remove the bolt make sure you catch the spacer that sits between the brackets.

Finally, hook the belt off the top pulley and let it fall away (picture 3), note it goes over the front rut in the crank pulley



 

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Step 4 - Now it is just a case of (patiently) removing the 5mm allen key bolt that holds the sensor in place. The quickest way I found was just using a standard allen key and turning 1/4 turn at a time




Step 5 - Now we turn our attention to the connector which can be found up at the top of the engine, you need to unhook the metal retainer (just a small flatblade screwdriver will do) then it pulls apart. The metal piece is highlighted on the first picture




Step 6 - Removing the sensor from the block is a little awkward, it will probably resist! Using the base of the cable entry wriggle the sensor back and forth (a small amount at first then bigger movements until it is free), then you need to get your fingers round it and pull it clear, it will just pull out as shown on the picture. If you are not replacing the sensor then use the flange to rotate it so you don't stress the wire.

 

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Step 7 - You may find debris on the sensor in which case you can try cleaning it up and refitting it to get a clean signal. It is not uncommong for a cps to drop out of spec though so don't bank on this working most of the time




Step 8 - Thread the sensor out (push the connector down rather than pulling the sensor up) and then get your nice new one ready to fit



Step 9 - Feed the connector end up from the crank end as shown in the first picture. There is a tight spot where one of the mounting brackets sits but it will wriggle through (shown in picture 2)


 

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Step 10 - You should be able to get your fingers to the connector between the pulleys as shown in the first picture then work your way back up to rejoin the connectors (ensure the locking tab you removed in step 5 is back in place so it clicks in).




Step 11 - Now put the new sensor in the block (leave the allen bolt in while fitting it and hold it in place with your finger as you put the sensor in), after a couple of goes with the allen key the thread will bite and, 1/4 turn at a time, you can tighten it up




Step 12 - If you removed the aircon belt, refit it (picture 1) and the nut/bolt/spacer (picture 2) whilst applying tension with a pry bar or similar (picture 3) then tighten the large allen key bolt (picture 4)




 

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Discussion Starter #6
Step 13 - For the rear sensor you will want the car up in the air, jack from the front on the mounting bracket shown with a 2 ton+ trolley jack




Step 14 - Looking up from just behind the nearside front wheel you should be able to easily see the rear sensor (first picture) which is held in with a 10mm hex head bolt (picture 2)




Step 15 - Slacken the bolt and remove it then rotate the sensor (probably quite stiff) a few times just like in step 6 for the front sensor. Remove the sensor from the housing and be sure to catch all the little metal pieces that come out (fourth picture). These are little shims or spacers which set the clearance between the sensor and teeth.




 

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Step 16 - Pop up top and you will find the same 3 pin connector as the front used but this is located at the rear of the engine on the nearside and has little slack which makes things a bit awkward. Again, release the tab then slide the sensor out of the connector on the loom





Step 17 - Now this is the difficult bit, getting the old sensor wire out which is attached to the back of the block, access is terrible and there's no easy way, long pliers and willpower will help. Alternatively cut off both ends and leave a bit of cable attached to the engine!!

You can see from mine that this was in bad shape, the shielding was all exposed and covered in oil



Step 18 - Drop the new sensor down from the top and gently twist it back and forth to work your way down (picture 1). Route your connector underneath all the pipework in the engine bay to give as much slack as possible (you will need it), and plug it in (picture 2/3)



 

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Step 19 - Underneath, you want the sensor to come out between the mount and the engine block so it pops out right next to the mounting point as shown in the first picture. To do this you need to route the sensor as I attempted to show in the second picture! This is a view from underneath the car lying with my feet at the front of the engine looking up if that helps locate it!




Step 20 - Secure the sensor in place with the 10mm bolt (don't forget the shims), and use cable ties to ensure it stays put.

Note with regards to shims, strictly speaking you should measure the clearance between the tip of the sensor and the flexplate teeth and adjust as required but in reality, the sensors are likely to be identical in height so whatever shim was used before will work just fine.

 
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