I have a 92 400E that amongst pulling the codes one is for faulty knock sensors. I am not familiar with this part, what is it? What do they control? Any chance on knowing the location of the knock sensor on my car.....Thanks for the info.

iirc, the knock sensor is the device that advances or retards the spark timing due to altitude or fuel octane.

__________________
Ben
1987 190d 2.5Turbo

The sensor itself is basically a microphone.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

So if you add Av Gas it will set timing up?

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

On M119 engines, the knock sensors are under the engine support arms that mount on each side of the engine.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
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44 years foreign automotive repair
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

There are two interchangeable part numbers available for your engine.

Sender unit, knock sensor
MB# 0031534428
$330.00

Sender unit, knock sensor
MB# 0031534728
$330.00




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1983 300D
1984 190D
2003 Volvo V70
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These sensors would cause my car to stumble badly when I try to accelerate and occasionally idle rough?

Not likely. First thought on that is a vacuum leak. But a vacuum leak could cause issues that result in knock.

__________________
1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

It doesn't measure either, of course, but rather--as noted--"listens" for knocking and changes ignition advance until it goes away.

Lots of mythology out there that equates presence of these to being able to successfully use low-test gasoloine where premium is specified. This is not the reason for these things being installed and not in the design parameters.

__________________
Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

Exactly. Basically they are there to protect the engine when something is wrong, not to make-up for or correct an issue or allow one to ignore the issue. If knock is happening, something is wrong.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Yes, the knock sensor is literally a very sensitive microphone that listens for knocking. When you replace it the bolt must be torqued exactly for it to work properly.

You can test the knock sensor by tapping on the engine block with a metal hammer. That sounds just like a knock to the sensor and should upset the idle a bit.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Knock sensors CAN make the engine hesitate on acceleration!

However they have "little" to NO influence at idle

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I must be remembering the test procedure incorrectly then. I've only owned one gasser so it's not front burner knowledge Now that I think about it I do recall holding the RPMs up when doing that test.