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Thread: Replacing Knock Sensors

  1. #1
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    Replacing Knock Sensors

    RogRacer gave everyone the definitive knock sensor DIY a few months ago. I just replaced mine following his instructions and thought I would add a few things to help the next person looking at how to do this. This is a fairly major job, but it is an excellent time to replace the fuel filter and clean the ICV, etc.

    The usual caveats: All credit is due to RogRacer for the original DIY; proceed at your own risk according to your abilities; YMMV, etc.
    My additions are in blue.
    ___________________________
    From RogRacer's writeup:

    Knock Sensor Installation Instructions for ’95 M3

    Approach
    These instructions will explain how to replace the knock sensors on a ’95 US-Spec E36 M3 using the "from above" approach that requires removal of the intake manifold. On late-build ’95 M3s and beyond, it may be possible to replace the knock sensors using the "from below" approach by removing the starter and a few other things, but that approach is not possible on early-build cars like mine.

    These instructions will explain the "from above" approach as was required on my early-build ’95 M3. These instructions may also be useful for any early M50, and perhaps M52s if using the "from above" approach, but as always, YMMV. (As a side note, if you just need to replace the number 1 sensor, you can get to it without removing the manifold and you can skip all this stuff) Other cars may differ, but there is no way that this could be done on my car. I had to take the manifold and ICV off to get to the connector - even for #1.

    Parts
    Two (2) knock sensors. You’d be nuts to replace just one sensor if you’re going to the trouble of removing the manifold (no kidding!!). They’re only about 50 bucks each. I’d also suggest new manifold gaskets and a new throttle body gasket. You may also want a new set of fuel-injector O-rings, but I didn’t bother. You’ll also need some new hose-clamps for the fuel lines. This is also a good time to put in a new fuel filter so you might also want to get one of those too. Also - be prepared to replace vacuum line on the fuel pressure regulator - it cracks with age/heat.

    Tools
    Just the usual assorted wrenches, sockets (mostly 10 and 13 mm), extensions and swivels. You’ll also want an inspection mirror, a magnet to pick up dropped fasteners, and some petroleum jelly.

    Instructions
    1) Remove the #18 fuse to kill the fuel pump and try to start the car. The car will not start, but the fuel system will depressurize. Actually mine started and ran for about 15 seconds.

    2) If you’re going to replace the fuel filter, you will need to get the car up on ramps or jack stands. Otherwise, you can perform the entire procedure with the car on the ground.

    3) Disconnect the battery, because you’ll be working around the starter and alternator and welding is not part of any of these instructions. (No kidding - the starter is RIGHT THERE and you will contact it.)

    4) Remove the intake system from the filter all the way back to the throttle body.

    5) Remove the alternator-cooling duct.

    6) Remove the cosmetic plastic covers for the valve cover and fuel-injection harness.

    7) If you’re replacing the fuel filter (on early build cars), this is a good time to do it. Get to the top filter clamp from above the car, and the lower one from below. Be prepared for a significant amount of fuel spillage with a catch-tray, but once the filter drains, the flow will stop. After the new filter is in, you can put the car back on the ground, but I left mine up on ramps because I found it useful to look at things from "underneath" at times, and to make collecting the dropped fasteners a little easier. I found it easier to replace the fuel filter on my early build (8/94) AFTER I had the manifold off.

    8) The next few steps (9-13) are all required so you can get to the rear most manifold nut, which is obscured by the fuel rail, the pressure regulator, and the wire harness box at the firewall. It is my understanding that some cars can access this nut without doing all this, so you may want to check before proceeding. I think Roger's suggestion to do all of this is absolutely right and is the difference in making the job workable. This greatly improves access.

    9) Remove the windshield wiper arms. On my car, this was easier said than done. The arms are pressed onto a spline and are a tight fit. You need to wiggle them while pulling them off. Mine were on so tight, I ended up using a puller, but you might get by with a screwdriver to pry them off.

    10) Remove the plastic cowling beneath the wipers. You don't have to remove it completely. I just removed the little screws holding down and lifted it up as needed. It is a pain to replace in the corners if you remove it all the way.

    11) Remove the DME from it’s compartment in the firewall and separate it from the wire harness connector.

    12) Unscrew the harness box from the lower cowling underneath the wipers.

    13) Remove the lower cowling (2 screws on passenger side, one on the drivers). Essential for easing the work in the rear of the manifold.

    14) Cut the wire-tie above the brake booster, and pull the wire harness as far up off the manifold has possible to gain clearance with the rear most manifold nut. Temporarily secure the harness in this position with a tie-wrap or string.

    15) Disconnect the electrical connector at the throttle body and unbolt the throttle body from the manifold. Leave the all the hoses attached to the throttle body.

    16) Using the inspection mirror, look under the manifold at the Idle Control Valve vacuum hose attachment to the manifold. It is held in place with a finger-clip type latch. You press up on this latch while pulling the large hose out of the manifold, but, again, it is easier said than done. I needed to put a small flat- head screwdriver in the latch to help coax it out. This was impossible for me to remove so I removed everything else, pulled the BACK end of this hose off the ICV, then took the manifold off, flipped it over and removed this as the last connection.

    17) Remove the front and back side manifold support brackets. I removed the bolts that connect the brackets to the manifold. The rearmost one has another bracket sandwiched in with it than holds fuel lines.

    18) Remove the fuel line from the front side of the fuel rail. Note that this is secured with a one-time clamp, like the other fuel line clamps, so you’ll need to use new ones for the install.

    19) Remove the brake booster vacuum line at the manifold. Again, you will need a new clamp. Mine just pulled off and pushed back on. No need to replace or diddle with the clamp.

    20) Remove the vacuum line at the fuel pressure regulator (no tools required, just pull it off). I had to replace this hose. It was old and hard and rotten. A real pain.

    21) Remove the wire that runs to the fuel injection harness from the Vanos securing bolt.

    22) Remove the nuts securing the wire harness box and fuel injection rail to the manifold.

    23) Remove the restraining clips that anchor the coil wires to the valve cover to gain a little freedom of movement in the fuel injection harness.

    24) Next, you need to remove the fuel rail/harness/injectors from the manifold as an assembly (they stay together as a unit). However, you will note that you have not yet removed the rear fuel line at the fuel rail. This is because the rubber hose is so short that it lacks the flexibility to pull off the rail with the fuel rail in place. So, as you remove the rail/harness/injectors from the manifold, you will simultaneously pull the fuel line off the rear of the rail. Work slowly, and remove the rail/harness/injectors off the manifold by pulling upward. Set the assembly back over the valve cover as far as it will go and secure with temporary cable-ties. This is a bit tricky - the injectors are plastic and fragile (and $70-80 each!). You need to be gentle in removing and reinstalling and even in how you sit it aside. I did tie it off, but I placed it on a towel. This is another area where taking the lower cowl out makes a big difference in freedom of movement. Some people take 1 or 2 injectors out to help. I left them all in.

    25) Unclip the hard fuel line from the front underside of the manifold.

    26) Unscrew the retaining nuts on the manifold. These are 11mm nuts and access to the 7th in the rear is made feasible by removing the lower cowl.

    27) Pull the manifold from the cylinder head. Before you do this, blow the grit and dust off to keep particles from falling in your intake ports. As you begin pulling it off, reach under the manifold and disconnect the electrical connector from the Intake Air Temp sensor. The intake manifold should now be in your hands. The only thing dangling from it should be the vacuum line to the pressure regulator. Removing the manifold requires even pulls across the whole length of it. It takes patience.

    28) Take this opportunity to inspect your intake valves. Mine had no significant carbon deposits! Gotta love Mobil gas with regular shots of Techron! Cover the intake openings with clean shop towels to prevent crap from getting in there while open.

    28a) Significant addition: In my car, I could see the knock sensor heads, but not the connectors. I had to remove the ICV to expose the connector portions (and even then it took some time to figure out which connectors belonged the knock sensors.) So - remove the ICV. A good time to clean it out and get rid of that erratic idle that 95 M3's seemed to have. (at least mine did). I also replaced my fuel filter at this time.

    29) Remove the Number 1 knock sensor and wire connector,
    noting the orientation of the sensor on the mounting boss. Clean the mounting surface, and replace with a new sensor. Use a torque wrench and torque to 15 ft-lb. You have to feed the sensor connector behind some other stuff to get it in place.

    30) To get to the Number 2 sensor, you need to remove a bracket that sits over it. Once that is done, replace the sensor like you did on Number 1.

    31) Replace the intake manifold and throttle-body gaskets and lube with petroleum jelly. Lube the fuel injectors o-rings, as well as any vacuum line fittings with rubber-type sealing rings.

    32) Reassemble reversing the steps above. The biggest headache that I had on reassembly was rebolting the brackets to the bottom of the manifold. Two things helped: 1) don't tighten the manifold to the engine completely - allow some give. 2) loosen (but don't remove!) the lower mounting bolt on the bracket (esp rear) to allow some extra given while you blindly line it up with the hole on the manifold.

    33) Let the fuel pump run a while before starting the car. Use this opportunity to reset any stored codes with your Peake Reset tool. If you don’t have one, I believe the stored codes will clear after 10 starts (assuming no additional faults). It may take several attempts to get the car to start. When it does, the idle may be erratic, but it will soon settle down and be smooth once the DME adapts. It took 3 tries to start, but when it did it ran very smoothly.

    34) That’s it! Enjoy life without those annoying CE light flashes! Agreed!! Could not have done it without these instructions. Thanks RogRacer!!!!!!
    2006 Z4 3.0 si
    6 spd


    2004 325i auto (DD). GONE.

    2013 Honda Ridgeline

  2. #2
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    I've had replacements for about 1.5 years now but haven't got around to putting them in. Did you notice any differance in the engine after replacing them?
    Dakar 95 M3 (4/95 manufacture)
    Techno Violet 97 M3 (12/96 manufacture)
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    "I have no idols. I admire work, dedication and competence." -- A. Senna
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  3. #3
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    Quote Originally Posted by Casebrius
    I've had replacements for about 1.5 years now but haven't got around to putting them in. Did you notice any differance in the engine after replacing them?
    Besides the absence of occasional CEL?

    Yes and no. When first driven, the car revved smoothly, but felt sluggish and stumbled a bit - probably from adapting after having the battery disconnected. After the first drive, it has run great - with no CEL's. It seems like I used to get an odd stumble occasionally under acceleration before (knock sensor kicking in to retard timing?). THat seems to be gone.

    The old sensors were visibly cracked when I removed them. Clearly a job that had to be done.

    Jeff
    2006 Z4 3.0 si
    6 spd


    2004 325i auto (DD). GONE.

    2013 Honda Ridgeline

  4. #4
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    Nice additions to the write-up M3Griff!

  5. #5
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    This link rulez. Thanks.
    PM is full. Do not PM me. EMAIL me to communicate!!

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  6. #6
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    Quote Originally Posted by M3griff
    Besides the absence of occasional CEL?

    Yes and no. When first driven, the car revved smoothly, but felt sluggish and stumbled a bit - probably from adapting after having the battery disconnected. After the first drive, it has run great - with no CEL's. It seems like I used to get an odd stumble occasionally under acceleration before (knock sensor kicking in to retard timing?). THat seems to be gone.

    The old sensors were visibly cracked when I removed them. Clearly a job that had to be done.

    Jeff

    Sorry, for bringing this up back from the dead, but my car has been having the same symptoms....

    Did you notice any better performance or gas mileage from changing the knock sensor. Mine did this a while ago and I ran a full tank of High Octane Gas and it went away, but is now coming back. I need to replace my Fuel Filter soon as well. Just wondering if it has affected your performance in any way?

  7. #7
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    Quote Originally Posted by m3beemer16
    Sorry, for bringing this up back from the dead, but my car has been having the same symptoms....

    Did you notice any better performance or gas mileage from changing the knock sensor. Mine did this a while ago and I ran a full tank of High Octane Gas and it went away, but is now coming back. I need to replace my Fuel Filter soon as well. Just wondering if it has affected your performance in any way?
    Well - I did notice that the car quit flashing the CEL and quit stumbling (concurrent with the flashes). Otherwise, no difference. If you have a 95 M3, you can replace the fuel filter while doing the knock sensor replace. But, before you do anything, read the CEL codes.
    2006 Z4 3.0 si
    6 spd


    2004 325i auto (DD). GONE.

    2013 Honda Ridgeline

  8. #8
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    Quote Originally Posted by m3beemer16
    Sorry, for bringing this up back from the dead, but my car has been having the same symptoms....
    Did you check your codes?
    Dakar 95 M3 (4/95 manufacture)
    Techno Violet 97 M3 (12/96 manufacture)
    ___________________________________
    "I have no idols. I admire work, dedication and competence." -- A. Senna
    Illegitimus Non Tatum Carborundum

  9. #9
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    Quote Originally Posted by Casebrius
    Did you check your codes?

    Yea, its registering knock sensor.

  10. #10
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    Ok did it but one problem

    Hey guys this is my first post... I followed your write up and sure enough one of my knock sensors was cracked. But now I have a problem, I do not have a tool to clear the codes and now my check engine light is on all the time with only the same knock sensor code. is this normal and how do I get it to go away?

  11. #11
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    No, that is not normal. In fact, I've never heard of the CE light being on continuously with a knock sensor code. Are you sure that is the stored code?

  12. #12
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    1226

    yea the only code is 1 2 2 6...

  13. #13
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    Interesting....and the CE light is on constantly? I've never heard of that with a knock sensor fault. You must have a problem beyond the "normal" knock sensor code. You sure you got the connectors properly seated? In any case, I'd clear the code, and see what happens. If it immediately comes back...with the CE light constantly on....I'd say it's a wiring problem or the sensor you installed is bad....

    BTW...I think you will need a Peake reader to clear the code.....

  14. #14
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    Quote Originally Posted by RogRacer
    Interesting....and the CE light is on constantly? I've never heard of that with a knock sensor fault. You must have a problem beyond the "normal" knock sensor code. You sure you got the connectors properly seated? In any case, I'd clear the code, and see what happens. If it immediately comes back...with the CE light constantly on....I'd say it's a wiring problem or the sensor you installed is bad....

    BTW...I think you will need a Peake reader to clear the code.....

    After I replaced my knock sensors, I also got a continuous CEL. I took everything back apart, cleaned the knock sensor mounting points (use electrical contact grease) and retorqued VERY carefully (I think overtorquing was my problem). No more CEL. I thought that the CEL cleared itself when no source of problems was around. (unlike the SRS light). Don't worry - the second time getting to the sensors was MUCH faster due to the practice

    Hope this helps
    2006 Z4 3.0 si
    6 spd


    2004 325i auto (DD). GONE.

    2013 Honda Ridgeline

  15. #15
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    Well I learned something! There must be at least 2 levels of severity with the knock sensor codes: 1) an intermittent flashing of the CE light at about 4 k rpm and light throttle, and 2) a continuous CE light.

    On my own car, I've only experienced Case 1. I guess the stored code is the same regardless....but I wonder if there is an effect of ignition retard between the two cases........

  16. #16
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    Quote Originally Posted by RogRacer
    Well I learned something! There must be at least 2 levels of severity with the knock sensor codes: 1) an intermittent flashing of the CE light at about 4 k rpm and light throttle, and 2) a continuous CE light.

    On my own car, I've only experienced Case 1. I guess the stored code is the same regardless....but I wonder if there is an effect of ignition retard between the two cases........
    Rog,

    Until I changed out my sensors, I had only experienced Case 1. I did the swap on a Sat. and all was fine until Monday afternoon when my CEL came on and stayed on (your Case 2). The code was 1226. It did feel like the ignition was retarded, but I was so sick about it that it would have felt different regardless. I drove around trying to tell what was happening - and ended up getting stopped by a cop - who asked what I was doing (running from 45 to 65 and back on a 45 road, revving the engine up and down, etc.). I showed him the CEL and explained - he started asking about the car - how many miles (120K), what year, etc., so I figured he was OK. No ticket!!
    2006 Z4 3.0 si
    6 spd


    2004 325i auto (DD). GONE.

    2013 Honda Ridgeline

  17. #17
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    Man I just payed bank to get new ones in last week.

  18. #18
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    Quote Originally Posted by Mr.Cosmos
    Man I just payed bank to get new ones in last week.

    Sorry! Ain't it fun, though!
    2006 Z4 3.0 si
    6 spd


    2004 325i auto (DD). GONE.

    2013 Honda Ridgeline

  19. #19
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    Success!!!

    Well I found out that I did not reconnect the Intake Air Temperature sensor on the manifold all the way. So I had to fumbling around where I couldn’t see to reconnecting it. Then I unplugged the battery for 5 min to clear the codes, thanks heifetz17. So no more codes and the car runs great. M3griff thanks for the write up. Everyone else thanks for your input. To anyone else who has this error defiantly get it fix, I noticed a good performance difference when I was coming out of my neighborhood sideway . anyways Thanks again

  20. #20
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    I replaced BOTH sensors without removing intake.

    It is possible, but you have to do it arthroscopicly using retrieval magnets and mechanical grabbers normally used to retrieve dropped nuts and bolts. Also had to use heavy gauge wire to pull the sensor up the side of the engine and work my hand back in well enough to thread the bolt on. It amounts to how well your creative mind can keep you from going insane and get it done.

    FitzRoger
    HotRedM3
    ..............Form following function; the true pathway to beauty..............

  21. #21
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    Quote Originally Posted by FitzRoger
    It is possible, but you have to do it arthroscopicly using retrieval magnets and mechanical grabbers normally used to retrieve dropped nuts and bolts. Also had to use heavy gauge wire to pull the sensor up the side of the engine and work my hand back in well enough to thread the bolt on. It amounts to how well your creative mind can keep you from going insane and get it done.

    FitzRoger
    HotRedM3
    Bet you didn't use a torque wrench.

  22. #22
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    This is true but I could have. 15 foot pounds isn't hard to judge when you've done it enough. The bracket covering #2 isn't being used on my car, so it is now residing on the workbench. I reinstalled the left bracket bolt, which is being used to hold a second loom bracket. Bottom line is, the car runs great and I am happy. :atom

    FitzRoger
    ..............Form following function; the true pathway to beauty..............

  23. #23
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    Sorry to bump an old thread, but I was curious about the part numbers for the knock sensors. Via realoem.com I could only find one part number for a ping sensor.

    Is this part number for both knock sensor 1 and 2?

  24. #24
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    Quote Originally Posted by SQ Bimmer
    Sorry to bump an old thread, but I was curious about the part numbers for the knock sensors. Via realoem.com I could only find one part number for a ping sensor.

    Is this part number for both knock sensor 1 and 2?
    yes.
    Just bought mine.
    Highend Landscape Lighting in Florida.
    Check us out!
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    /


  25. #25
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    OK thanks, wasn't sure! Will be ordering two of these puppies here shortly.

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