Remotecontroller

Hey Folks,

I got a fault code on my 94 968 which is for Knock Sensor #2, but after searching numerous sites and threads haven't been able to discern whether #2 is the front or rear knock sensor. Anybody know off hand?

Thanks in advance!

968workaholic

Rear, the one that needs the intake manifold to come off unfortunately

spanky

I know this is a old thread but I thought I would pass on the good news that the 968 # 2 knock sensor can be removed and replaced very quickly WITHOUT removal of the intake manifold. I did mine today and replacement of the # 2 sensor took all of 7 min.
1.Locate # 2 knock sensor : its located on top of and near the rear of the cylinder head 6 inches to the left of the engine oil separator.
2.Gather reqd tools: 1/4" drive 13 mm flex shallow 6 point socket
1/4 long extension
1/4 long handle ratchet.
1 long elect wire tie wrap
2 small/short elect tie wrap
1 long handle needle nose 90 deg bend
1 Flat head screw driver
Lets get started.
1. Loosen the hose clamp on the large vacuum pipe that is located under the intake manifold, directly in front and above the sensor, rotate the hose clamp out of your way.
2. Move to the very end of the intake manifold directly above the oil seperator and insert the 1/4 extension until you can see its end near the knock sensor that's to be removed. Using the 90 deg needle nose insert the 13 mm flex socket onto the extension.
3. Insert ratchet onto the 1/4 long extension,
4.Place the 13 mm flex socket onto the sensor bolt head and leave it in place
5. Using the 90 deg needle nose remove the wire connecter from the sensor, be gentle, this stuff is old.
6. Loosen the sensor bolt and back it out completely. remove sensor and toss.
REMOVE THE RATCHET from the extension!!!
SAVE THE BOLT!!!! It has blue lock tight on it and can be reused.
7. Take the new sensor and place the small tie wrap around the neck of the sensor, tighten it snugly
8. Take the large tie wrap and threat its tip through the small tie wrap about 2" then fold this back and use the 2nd tie wrap to secure the folded section of large tie wrap in place.
9.Insert the bolt into the eye of the sensor.
10. Now using the large tie wrap as a handle position the new sensor into it correct position with the sensor neck at the 11 o clcck position use the extension to start catching a thread and tighten the bolt by hand until its snug.
11b. Using wire snips cut the tie wraps from the new sensor neck.
11. Install the wire plug connector after cleaning with contact cleaner.
12. Position the sensor neck to the 12 o clock position and torque sensor tightly
using the 13mm socket , extension and ratchet. Spec is 15 ft/ pounds or 25 nM
13.Remove your ratchet, extension and flex socket
14. Rotate the large vac line hose clamp back into its correct position and tighten the clamp
This should take less than 30/45 min start to finish for both sensors
I hope this will be helpful in the future for this job.
Pls post comments as you see fit. Thanks.

thomasmryan

those bolts need a drop of blue Loctite. orientation of both sensors should be noted before removal.

Boeing 717

Any noticeable benefit?

spanky

Boeing: Yes,the #2 knock sensor code / check engine light cleared within 100 feet of my driveway on the test drive and remained clear. Engine timing isn't being retarded due to this knock sensor code being present. Full smooth power from my engine. Its nice!!
Thomasmryan: THANKS> I made note of both of the old sensors orientation before removal and positioned each new sensor exactly as I found the original sensor

touareg

Thanks!

Did you do anything to compensate for the torque down using the flex socket?

spanky

Touareg: No I did not, should this be a worry for me?

Nathan J.

By coincidence, I just replaced both of the knock sensors on my car, also using a flexible 1/4 socket to loosen up the bolt.

In the process of removing the rear sensor, I broke the one of the thin vacuum lines that run under the intake manifold, and over the knock sensor. In tracing the remaining hose, it appears to feed a vacuum valve next to power steering fluid reservoir. The other end is spliced near the firewall to a blue hose of the same diameter that goes away on the left hand side. I have never dealt with thin vacuum hose like this, it is about 1/8 " in diameter. Does anyone know the part number for this hose, or the part number for the valve it connects to?

Thanks

Nathan

thomasmryan

there are a couple sizes but your local Mercedes dealer will sell it by the meter. measure you broken section or take it with you.

it gets brittle over time and the rubber elbows get mushy if any oil has been run through the line.

edit. that particular line runs to your heater valve

touareg

I am no expert, I just worry! I was asking to learn, I don't have any opinions other than following it the best I can.

Opinions no facts here: https://www.garagejournal.com/forum/...p/t-19707.html

Nathan J.

Thomas,

Thanks for the feedback on vacuum hose. It turns out this is 4mm OD hose (0.16"), and I have have some on order from an online hose

Nathan

thomasmryan

The vaccuum line for the heater should inserrt into a T or Y fitting back by the firewall. The AOS has a small rubber elbow on the top of the housing that had turned to mush from oil ingestion. It was plugged enough not to be a vacuum leak but you might run some filament, weed eater or otherwise, to be sure nothing has been sucked into the loose ends.

Nathan J.

Thomas,

Thanks for the tip, I will certainly check for any plugs before buttoning the system back up.

One other question regarding your earlier comment on the orientation of the knock sensors how critical is this? I did not realize when doing the job that this mattered at all, and while I am sure I am within 20 degrees of the original sensors with my replacements (because the electrical wires dictate the position to a large degree), but I did not note the original position so I am guessing how close or far from perfect I am? I did take the car out for a drive, and the CEL went off (yeh), although I have not yet attached the Durametric to check for codes.

Thanks

Nathan

jsheiry

Thomas, I had my check engine light come on recently on my wifes tip car that I just rebuilt. Happened just after I mashed the accellerator in an off ramp to feel her perform. Now because its a tip it took a moment to kick down the gear and then accellerate.(perhaps there was actual knocking from poor quality gas whilst trying to get the tip to downshift. Been putting 93 in her since rebuild but you never know what your going to get) After I parked the car and then drove the next day after 4-5 miles the light went out. I checked it at home with the durametric and it had stored Knock Sensor 2, Knock Sensor 1, Knock Sensor 2. I removed these codes from memory and will keep and eye on it. I only placed the knock sensors where they seemed to have been and clearly no pictures of this were taken. They look to have smooth backs to interface with the block but no indication of any orientation issues except obviously the wiring harness will demand some reasonableness.