Knock sensor....

[Dopefish]

Okay, this is getting very frustrating because I can't get this damn errorcode to go away. The light was on when I bought the car and everyone says that it is like a new car when it isnt pulling the timing due to a failing knock sensor...

I installed a 1 MOhm 1/2w resistor directly to the ECU harness(back-probed), Pin (KNOCK) to Pin (GND).

After clearing my ECU (removed + batt. terminal) and driving the car for a bit, no real performance gain and the code came back on.

I found a NEW OE sensor for $68 and I am starting to conside it. However, my concern is that another issue is lurking due the resistor trick failing. Another reason I'm wanting to forgo buying the sensor now is due to the harness connector being broken now. (when I was diag'ing it one of the pins pulled out and the connector itself broke apart) I'm sourcing a new connector from a spare car I have.

My car is a 1995 240sx 5spd (OBD-I). I run regular 89 since gas is so expensive but I tried a tank of 93 and reset the ECU to find no improvements. I would think that the ECU could detect octane and pull timing accordingly but not freak out due to the knock (considering all systems are working normally) so I dont think the gas is the issue. I've been having Discountauto pull the codes for me with their scanner, getting annoying driving over there every few days to see if I've gotten rid of one of the codes (I have another for speed sensor, which is strange as my speedometer is on target and another for emissions control).

What are your thoughts?

~Kris

[MELLO*SOS]

I had faulty knock sensor wiring harness, and did that resistor trick. It worked great for me, curing my S13/KA24DE code 34.

Maybe your ground on the resistor isn't good? I just ran it from the KS pin to the resistor to the chassis near the ECU after checking with my DMM. If it's not grounding properly the code 34 will come right back.

GL & maybe the other members have some ideas for you...

[Dopefish]

Originally Posted by mello88

Maybe your ground on the resistor isn't good? I just ran it from the KS pin to the resistor to the chassis near the ECU after checking with my DMM. If it's not grounding properly the code 34 will come right back.

Thanks, it'd be nice if I could just override it for now (replace it once I get all my turbo bits) as I'd like to replace the suspension bushings right now and that $70 is a good chunk of my suspension investment pricing.

I'll try removing the lead going to the ECU GND and try to attach it at the chassis GND bolt next to the ECU. How did you have the lead going into the ECU? Did you back-probe the harness or splice it into the wiring?

Thanks,
~Kris

[Irukandji]

Strange.... my code went away after I filled up with 91 w/ octane booster (94ish?). But you said that didn't work. Just thought I would post this just in case someone else had this problem.

[MELLO*SOS]

Code 34 can mean a bad knock sensor and/or bad wiring to the KS -- if you just unplug it or have a short there it'll come right back. I ended up having a short somewhere in the KS subharness. The KS itself tested fine, along with the wiring from the ECU up until the KS subharness connector.

Originally Posted by KS problem guy

Did you back-probe the harness or splice it into the wiring?

I snipped the wire (white, pin 27 iirc?) from the harness side of the connector, soldered on the resistor, then ran a wire from the other side of the resistor off to the chassis ground. Be sure to check with a 12v test light or a DMM to make sure that you're grounding to a good spot on the chassis, otherwise the code won't go away...

GL

edit: you are getting a code 34, right?

[ledzeppelin240]

Yeah have you checked the OHMs of the KS wiring? Maybe the engine is actually detonating?

[240shorty]

I wired one in on my previous engine. I spliced into the harness before the knock sensor harness and ran through the resistor to ground. Basically wired it so that the resistor replaced the sensor. I found this to give the same exact voltage as routing it across the harness terminals as some others have done. The major plus being it is easily removable if you replace the sensor.

The 1Meg resistor eliminated the code, but... I tested the ECU terminal and the resulting voltage at the ECU was 3+ volts. The FSM calls for 2 - 3 volts at idle. So I was concerned that though the DTC was gone, my timing might still be retarded. I replaced the 1 Meg resistor with a 1 Meg POT and dialed the resistance down somewhere in the 750 KiloOhm range (guestimating here). This resulted in a constant voltage of ~2.15, which is in spec. You should manually clear the ECU. If the fix works, it will be apparent immediately. The ECU recognizes the faulty circuit when power is on. If the code doesn't reappear right away, you should be golden.

I should note that at no point did my cars performance noticably improve. I believe I had other mechanical issues. I now have a fresh engine in and wouldn't you know... faulty knock sensor.

Oh, and who carries the Knock Sensor for $68??

[Dopefish]

It is a code34 for sure, and the wire I backprobed was white, I had the pinout but cannot find it now.

I'll have to take another look at the wiring to the sensor. Before I wired the resistor to the ECU harness I tried connecting it from the connector before the sub-harness and it still didnt work. I might cut the wire from the ECU harness just to elimenate the possibility of shorting out somewhere, if that turns out to be my issue I'll run a new wire to the KS and wish for the best.

~Kris

[240shorty]

Originally Posted by 240shorty

Oh, and who carries the Knock Sensor for $68??

Pretty please??!?? Or is it not from a retailer? That would be cheaper than Ebay prices.

[Buffalo Daughter]

dood have you ever though that your 89 pump gas is causing the knock??? cars do have specified octane and although it will prolly cause pinging and detonation knock is relatively related to spark plugs, plug wires, distributor. If is a faulty connector you should first test the connection to see if you getting voltage. Then check the knock sensor physically. If all else fails replace the bitch because they do tend to go out after a while.

[BOROSUN]

tip: if your knock sensor is on too tight, it can react too responsive!

just learned that today. ;p

[Dopefish]

What is the torque spec for the knock sensor, or is it just a hand tight with Lok-Tite on the threads?

I may be taking off the intake mani this weekend, cleaning some stuff up, removing emissions and hopefully working on the KS issue.

Thanks,
~Kris