Question about 1992 Lexus Sc 400

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Do i have to take off the intake manifold on a 92 lexus sc400 to replace a knock sensor

Do i have to take the intake manifold off to replace the knock sensor

Posted by Anonymous on

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6 Suggested Answers

6ya6ya
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Posted on Jan 02, 2017

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  • 36 Answers

SOURCE: 92 lexus es300 knock sensor

Need to remove the upper and lower air intake manifold.  There are two knock sensors for the front and rear pistons banks.  If you plan to do this yourself it is about 1 to 2 hours.  While you are at it, there is a short coolant bypass hose sitting in the same spot, replace it.  Another problem with the knock sensor is the wire harness used to connect the two knock sensors into one connection sometimes wears out and contacts the metal on the engine causing false signals to the ECM, so replace this cable also.
Just did this last summer on my 99 ES300.  Pretty easy.
DIYr

Posted on Mar 16, 2009

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  • 36 Answers

SOURCE: Have a 1999 lexus es300.

If you have some common tools the knock sensors are no big deal.  If you take a lexus they will make is sound like you need to completely disassemble the engine and scare you off.
First, do you really have a problem with preignition causing real knocking due to carbon buildup, or diluted gasoline or do you have failed knock sensor(s).  Try to decarbon the engine first.
There is a technique used with water being sprayed into a warm engine intake.  This will clean up the valves and carbon buildup which can result in engine knocking.  

The job will be a couple hundred for the parts and a couple hours of your time.  After you are done, you have entitled yourself to approximately $500 in new tools for your tool chest since this is what Toyota and Lexus will charge to fix (about $1k+).

You will need to buy the following to address the knock sensors and a couple other items while you're in the neighborhood.
- 1x upper intake plenum gaskets - 2x lower intake plenum gasket - coolant bypass hose found in the same area as knock sensors - 2x knock sensors (bank1 and bank2) - short pig tail cable which connects both knock sensors to common wire harness. - toyota antifreeze  (2 gallons, if i remember correctly... when mixed to 50/50 (antifreeze/ water) you will have 4 gallons.
drain the radiator drain the front of the engine using the engine drain plug - this plug is on the front right side facing the engine, behind the right hand exhaust manifold. (this will lower antifreeze enough to avoid dumping antifreeze all over the engine later) remove the air filter box remove the connections into the throttle body remove the cable from the throttle control remove the upper air intake plenum remove the two lower air intake plenums remove the antifreeze fill port
Knock sensors will be in the valley between the lower intake plenums.  You will need to remove the rubber antifreeze bypass hose (little short hose blocking access to the knock sensors).
By the way, the reason you bought a replacement, is that if this short hose splits from normal wear, you need to spend this money and effort to reach it, so just do it now.
The little pig tail cable which connects both knock sensors to the wire harness is said to cause a big majority of the problem due to the plastic getting hot and brittle, falling off and shorting to the engine.  While in this mode the engine thinks knock is occuring and starts to retune the air fuel mixture to get rid of the knock until it goes into minimal operations mode.
After replacing the knock sensors (and tighten to torque specs), replacing pig tail cable, and reinstalling your new short by pass hose.  Replace the lower gaskets, antifreeze fill port, lower intakes, upper gasket, upper intake, air intake, air filter, reattach everything, reconnect all the rubber lines you pulled off, make sure there are no splits in the air intake passage anywhere, retighten the engine antifreeze drain plug, and the drain on the bottom of your radiator, and your done!
Don't forget the easy stuff.  Dilute the antifreeze with water and fill the radiator and overflow tub.  Run the engine for several minutes until its hot and opens the thermistat to allow antifreeze into the empty engine cavities.  Turn the engine off and get a cold one as the engine cools.  Once absolutely sure engine is cold, refill the radiator with antifreeze and refill the reserve tub.  Do this at until all the beer is gone and you are both full of antifreeze (in one form or another)..... obviously red stuff in the car, amber down the gut.

Posted on Mar 16, 2009

Sean80000
  • 1867 Answers

SOURCE: Looking to buy 92 sc400...

Do yourself a favour and walk away unless you want to buy a big repair bill. Only a fool would consider buying a vehicle in this condition.

Posted on Jan 04, 2011

awcforever
  • 359 Answers

SOURCE: I removed the intake manifold,

Thats crazy, they should be underneath the manifold plain as day. I know this isn't the solution you were looking for, but that is exactly where they are located???

Posted on Mar 07, 2011

ginko
  • 19396 Answers

SOURCE: I need to know where

Hi.

The sensor is located in the cylinder head, on the driver side.

The sensor is represented as part nr.3 in the diagram below:

ginko_98.gif

Regards.

Ginko

Posted on Mar 27, 2011

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Hi,

This is a big job, you will need to remove the intake manifold and various other intake components to get to the knock sensor, which is sitting in the V gulley of the engine.

But basically you need to remove all inlet tract components, and the top cooling system components, then remove inlet manifold and there you will see the knock sensor.

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2 Answers

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Need to remove the upper and lower air intake manifold.  There are two knock sensors for the front and rear pistons banks.  If you plan to do this yourself it is about 1 to 2 hours.  While you are at it, there is a short coolant bypass hose sitting in the same spot, replace it.  Another problem with the knock sensor is the wire harness used to connect the two knock sensors into one connection sometimes wears out and contacts the metal on the engine causing false signals to the ECM, so replace this cable also.
Just did this last summer on my 99 ES300.  Pretty easy.
DIYr

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High RPMs


yes its related to knock sensor because car is running rich in fuel, and car runs of on safe mode, so overdrive will be off. have you and a friend replace it. remove intake assembly, then intake manifold, but first remove your anifreeze from radiator, trust me you want to remove antifreeze! their are brackets by the fire wall to hold down the manifold, thats the hard part is taking it off and putting that on since not to much space to work on it. on the block you'll see the two knock sensors, has 2 wires each, knock sensors cost between 150- 200 a piece, still cheaper than dealership putting it on. also buy some liquid gasket because you will need that. after putting it all back together reset the ecu and you should be fine,

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  1. located on top of engine below intake manifoldgraphic.aspx?mod=reptiff&module_id=1&session_id=%7ba7aa889f-b7e3-42e1-9ece-3476a2533f69%7d&image_guid=95d24086&print_bw=0&

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