ok , ecu codes, are they reliable?

[smithers584]

ok guys, car runs like shit. breaks up, like misfiring or timing getting pulled, on and off. ecu shows code 34. ok easy, knock sensor. shot all the wires and from the sensor to the ecu. they are perfect. so i go buy a new knock sensor and plug it in and bolt it up. nothing changes. WTF? are ecu codes not accurate, could something else be causing my ecu to think i have a knock sensor problem? i wouldnt think so. only thing i didnt think about doing was resetting the ecu after changing the sensor. does that matter in this case?

[Irukandji]

my KS light went away after I started filling up with premium

[smithers584]

ive never used anything but 93. any other ideas? could it be a cooling problem causing too much knock? my safc doesnt read any knock until my car starts acting up, when it reads knock it pulls timing. once it stops knocking the car runs good. but it all happens randomly, and it only takes a few seconds for the whole thing to happen then it goes away.

[drifter808]

How much Knock does the SAFC read? i get knock thats why after i been driving for awhile but i dont have any of those symptoms.

[smithers584]

it doesnt knock much, the highest it read was 12. the thing is that its just reading knock and then all of the sudden the timing gets pulled, but then when the timing straightens out the knock goes away. i think i will install a new knock sensor, but instead of putting it on the block i am going to try wrapping it in a rag and securing it somewhere so it cannot possibly read knock. then go out and drive and see what happens. any other ideas?

[drifter808]

i was thinking of tryin that to cause mine will read any where from 1-30 after i been driving hard for awhile. Try what you were saying and maybe it will fix it but i cant be to certain. post up what you find out.

[ericb382]

I don't think thats a good idea. If your knock sensor reads knock and backs off the timing, that means it is doing its job. It is saving your motor. If you pull it out, you prevent it from saving your motor. Would you rather have a loss of power for a few seconds, or a possibly blown motor?

[smithers584]

ok well its not my motor knocking, it just that the sensor is bad and causing my ecu to flip out. im just going to do this for troubleshooting purposes, not drive my car like that all the time. i think i will have to run a ground wire to the engine block though, because i pretty sure the sensor grounds itself, and if its not on the block it wont be grounded and i will have the same problem. can anyone confirm this?

[dopeassjackson]

just because you have a code for your knock sensor dosent mean that your knock sensor is bad. first off what kind of car do you have and what year?

make sure your fireing order is right and your timing is set at the correct place. also you have no need to run 93 unless you have a turbo. if your motor is mostly stock use 87 or 90 max. your knock sensor is used to adjust the timing. it will advance/retard timing until it sees the motor knock then back off a couple of degrese since your useing 93 octain your motor is having to advance/retard your timing way back until it sees it knock. since you have a code for a knock sensor i bet your motor isnt knocking with 93 in it and you ECU thinks that its not getting a signal from it. try putting some 87 in your tank and run it for a little.

[smithers584]

ok completly forgot to tell you guys its a s14 zenki with a s13 sr blacktop. timing and everything is good. i really cant find anything wrong with it, not even in the wiring, but here is my question. i replaced the sensor once, but forgot to reset the ecu, will it still think something is wrong until i reset it? or is it reset everytime i crank the motor?

[CHARLIE2020]

Disconnect the knock sensor sub harness and with a multi meter measure from the ECU (knock sensor) pin to chassis ground and measure your voltage with the ignition turned fully on but car not started and tell me what you get....

[smithers584]

ok i did check the ground and got like .4 ohms or something like that, and i checked the wires for continuity and didnt see any type of unusual resistance, but i have not checked for power yet, ill try and get that done and post.

[CHARLIE2020]

Originally Posted by smithers584

ok i did check the ground and got like .4 ohms or something like that, and i checked the wires for continuity and didnt see any type of unusual resistance, but i have not checked for power yet, ill try and get that done and post.

Trying doing what I said, if you have a short to ground your resistance is not really gonna change at all and it will appear as if all is good when its not and you will still have continuity.....trust me bro I've fixed 5 S13's and my own with the notorious knock sensor problem and im gonna give you some free advice but you gotta do the test I told you to...

Your most likely culprit is a short to ground in the knock sensor shielded line, all 5 of the S13's I fixed had a short to ground within 2 inchs of the same strech of harness in the same exact spot...

[drifter808]

this is helping me out to so im gonna give it a shot tomorrow.

[smithers584]

ok i will do it but you theory of shooting wires isnt completely correct (i do this for a living on F-16s, so i know a bit about wiring). not saying you are wrong because you are right with what you said, but if i had a wire that was shorted to ground, i would disconnect the ecu and the sensor, and take one lead and put it to a pin on the connector, and the other to ground. that right there tells me if my wire is shorted to ground. you are right though, you may not see a change due to the path of least resistance theory if you are shooting end to end, but you could also see a big change depending on how much of the wire is shorted to ground.

also, there are two wires that run to the knock sensor on my car, but only one of them actually goes into the connector, the other doesnt. is this normal? im asuming the second one isnt need because the knock sensor uses itself for a ground.

[CHARLIE2020]

Originally Posted by smithers584

ok i will do it but you theory of shooting wires isnt completely correct (i do this for a living on F-16s, so i know a bit about wiring). not saying you are wrong because you are right with what you said, but if i had a wire that was shorted to ground, i would disconnect the ecu and the sensor, and take one lead and put it to a pin on the connector, and the other to ground. that right there tells me if my wire is shorted to ground. you are right though, you may not see a change due to the path of least resistance theory if you are shooting end to end, but you could also see a big change depending on how much of the wire is shorted to ground.

also, there are two wires that run to the knock sensor on my car, but only one of them actually goes into the connector, the other doesnt. is this normal? im asuming the second one isnt need because the knock sensor uses itself for a ground.

I've tested every way imaginable isolated and unisolated......this is what happened the knock sensor signal wire with the shielding shorted to ground how it did it was like this the shielded part of the wire broke threw and made contact with the wire it is suppost to shield in all 5 cases therefore the signal now became ground.

A proper voltage reading at the ecu with everything in good working order should yield you ~2.5v at the ECU pin with the KOEO and with the knock sesnor disconnected it should yield you ~5v at the pin with KOEO, the load threw the knock sensor brings down the original supplied 5 volts from the ECU to 2.5v and as knock occurs the knock sesnor generates it own voltage which rides on top of the supplied voltage (2.5v) either increases or decreases the voltage in the presense or absense of knock....so voltage while running shoudl be above and below 2.5v as knock increases or decreases...

[CHARLIE2020]

The shielded knock sensor wire is diasy chained with many other grounds also...

[mrk9182]

Originally Posted by smithers584

also, there are two wires that run to the knock sensor on my car, but only one of them actually goes into the connector, the other doesnt. is this normal? im asuming the second one isnt need because the knock sensor uses itself for a ground.

Im not sure is this applies to sr motors but on most cars you need the 2 wires one is for the 5v reference signal from the ecu the other sends the modified signal from the knock sensor to the ecu

[CHARLIE2020]

No all knock sensors should run teh same exact way, there are two 2 wires (yes) but one is just the shielding wire coming together via a connector just so it can continue its path right up to the knock sesnor (sub harness) to provide shielding all teh way......the second wire just runs along the path of the knock sensor signal wire (its braided over it) it has no input back to the ECU what so ever unless it shorts to ground like it did in my cases. SR's are the same way.

[Buffalo Daughter]

so did you replace the harness completely with the knock sensor? I'm also currently goin through the same prob with my 95' ka motor. 215k on the motor. Knock sensor is going off. I'm getn v from the subharness but its going to be bitch take it off. What was the solution to all of this. From what i read its the knocksensor thats not groundingg righht? creating a short to ground??

[CHARLIE2020]

None of the cases I had was it a bad knock sesnor, the knock sensors where all fine......what I did to fix the problem was cut the shorted section out and re-solder the sensor wire backtogether making sure to keep it isolated from the shielding which lay right over it then covered it properly then I joined teh shield wire back together and re-soldered it back together and covered it apropriately then wraped it all together in electrial tap and all is fixed.....my gas milage went up right away throttle responce came back and the car is noticably more powerful than before.

Here's a good tip where to look for your short atleast on S13's, under the harness cover that is bolt on top of the fuel injectors, all 5 short to grounds I found on other car where all traced to that very spot just look for the black wire and follow its lenght and if yoru lucky you'll see a slight bulge where its shorted to ground..

[smithers584]

ok well i changed the knock sensor and everything is well now. really was easy to, kinda a tight squeeze, but if you do it make sure you have a 8 inch extension and a universal joint for the socket or you will regret it.