help-no reading from knock sensors

[mrq45ss]

i just replaced my knock sensors and when i put every thing back together. i tried to ohm them and didnt get a reading on my voltmeter. process i used to ohm knock sensor is neg pro of voltmeter on battery and positive prob to knock sensor pins. please if some one would explain to me why im not getting a reading from my knock sensors?

[qsiguy]

Your impedence reading should be directly through the sensor. Put one probe on one pin and the other probe on the other pin. You are looking for about .550 meg ohms or 550K ohms (same thing).

[LEMHEAD16]

Did you replace the harness as well? Mine was fried and giving me no readings. If you haven't you need to. It's pricey but a necessary part of a KS replacement job.

Infiniti of Scottsdale has them in stock. I think I paid around $130 for it. Make sure you tell them your a NICO member.

[newbissan-tech]

you guys do realize that nissan posted a bulletin a while back stating that when cars come in with a knock sensor code that it is most often caused by poor fuel quality, and to recommend higher grade of fuel. now that may not apply in this case but he should check the obvious first, wiring, voltage to sensor, ohm the sensor like lemhead16, said and controlled ground through ecm, etc. but what ever the case goodluck with your findings!
Modified by newbissan-tech at 3:01 PM 10/5/2009

[LEMHEAD16]

On an old VH motor I would almost 98.763% guarantee that it is not caused by poor fuel. I would be willing to bet his old knock sensors were cracked on the side and needed replacement along with the KS harness that has been baking underneath the plenum for 15-20 years now.

I would how ever concur with you if someone brought a much newer low mileage vehicle to me with a knock sensor code.

[newbissan-tech]

yeah dude you make a good point! but the possibilities are endless! although it wouldn't surprise me a bit if everything you just said is true!

[Q45tech]

Be sure to differentiate between 90-95 [OBD-I] and 96 to present [OBD-II].

I believe it wasn't until 2002 that the ecu became smart enough to actually diagnose a failed KS by any means other than the resistance test...........applying a small voltage and measuring the change of bias.

If you study the KS specification you'll see that the plastic housing was chosen as a historical marker of previous overheats.

Even without serious overheats the plastic will eventually fail [crack] from normal cycling after 10-15 years.

But as we all know plenum hoses will fail sooner so no excuse to not replace KS + harness when the plenum is off. Same with injector failure [5 require plenum removal] so another good chance to replace KS.

[mrq45ss]

need some help from the q45 guru's out there!

problems:

1- when i crank my engine to start froma cold start the rpms fly up to about 2000rpm usually it would stay there until it starts to warm up it it will drop down slowly the warmer it gets but now when i start up it jumps to 2000rpm and drop down immediatly to about 600-700rpm on a cold engine and stays there until it warms and they falls to 500rpm. any suggestions?

2-when i started up tonite someting even crazier happened. i left to get warm rite i know i put $15 in gas (93oc) rite bout 1/4 tank. when get in the car and get ready to drive off just b4 i put in reverse my eye caught the gas gauge and i was on empty.in my head i started bugging out sayon maybe i didnt put gas this morning. so i said ill go to the gas station. when i started driving i literally saw my gas gauge move back up to 1/4 tank from empty. i really went crazy and puzzled. i know i dont have a bad gas pump i tested and it tested fine. any suggestions?