KNOCK SENSOR

[Steve Fisher]

Does anyone know what the factory spec resistance reading is for the knock sensor? I have a 2002 W-22. I am reading about 100K ohms from the center connector to ground with it still on the vehicle. The wire to ground is about 4800 ohms with ignition off. I was told I had a bad sensor on the left bank but both sides read the same. Wireman

[mfire1339]

Steve,

If rain goes away tomorrow I will check mine.

mike

[tech@brazelsrv]

Steve,
The knock sensor should be between 93-107K ohms resistance. Do you have a trouble code indicating a bad sensor? Or are you hearing a ping? Check the torque setting, they should be between 11-14 ft lbs (no sealant or pipe thread tape)

[Steve Fisher]

Steve Brazel, I'm the guy whose motorhome you did the diagnostic test at Quartzsite. You recommended replacing the left bank knock sensor. Just for the heck of it I decided to take a resistance reading and compare it to the right bank sensor before I spent 50-60 bucks on a new one. Both read right at 100K ohms.It looks like they are both good.I also found 1 nut missing on the right header pipe flange and the pipe was pretty loose. Fixed that. The left side also needed tighting.That may have caused a bad o2 sensor reading that you said I had.Going to give it a run and see if I notice any differance. I also have a Scan Gauge II I bought from Kieth at RT.If the knock sensors are OK what should the MAX timing advance I should get.I think I'm getting about 41 degrees at 3000 RPM.sitting in the driveway, not on the road. Thanks

[tech@brazelsrv]

Steve,
Sorry I didn't recognize you...never got your name! Timing advance will vary depending on RPM
and load, 41 degrees with no load at 3000 RPM is normal. With the exhaust leak it will slew the computer to go rich, thinking it is running lean. Installing the bolt and tightening the exhaust should bring the readings back to normal.

[tech@brazelsrv]

Steve,
A couple more things I forgot to mention in my previous post. While you're at it set your DMM on the 400mv AC hertz scale and tap on the engine block near the knock sensor and see if you get a frequency reading. Also, make sure the torque setting is correct, I find that many times they are over-torqued. BTW, the reason I recommended replacing your knock sensor is that you had a stored trouble code saying it was out of range.

[Steve Fisher]

Steve, Is that done with the wire removed and test leads from the knock sensor pin to ground?With the resistance reading the same on both sides is it possible for the left sensor to be good even though it had a out of range code? Would I see another code on the the scan gauge since I asume you cleared when you ran the test? I'll probably just go ahead and replace it. Since I have been laid off for 6 months i'm just trying to watch my nickel & dimes but I sure don't whant to risk any damage. If it is out of range will the timing advance be retarded all the time? Also, what would the maximun timing advance I should see on the Scan Gauge under heavy load at say 4500 rpm? Thanks Steve

[tech@brazelsrv]

Steve,
I didn't clear the code and yes, unplug the sensor and test from the center plug on the sensor to ground. The timing will vary depending on load and rpm, at 4500rpm heavy load, you should see somewhere between 8 and 12 degrees of advance.