Post Reply 
 
Thread Rating:
  • 0 Votes - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Knock Sensor Test:
05-12-2014, 09:22 PM
Post: #1
Knock Sensor Test:
I was reading a 7 yr. old post on this forum where a factory trained Nissan technician used a timing light to check the knock sensor. Exactly how is that done. I want to try it. Any help is appreciated.
Find all posts by this user
Quote this message in a reply
05-12-2014, 11:46 PM
Post: #2
RE: Knock Sensor Test:
That was probably me as I was a Nissan master tech back in the mid 80's and I have been on this board for about 7 years.

The basics are hooking up the timing light in the normal fashion and finding the mark. Get a smalll hammer and tap on the side of the engine block rapidly and if everything is working correctly you should see the timing retard 5 - 10 degrees then come back after you stop. Other mechanical issues often cause the same reaction. (rod or lifter knock to name a few)

BTW, an open or shorted knock sensor will cause a check engine light so this is strictly a double check if you are looking for issues.
Find all posts by this user
Quote this message in a reply
05-13-2014, 07:41 PM
Post: #3
RE: Knock Sensor Test:
(05-12-2014 11:46 PM)Rupe Wrote:  That was probably me as I was a Nissan master tech back in the mid 80's and I have been on this board for about 7 years.

The basics are hooking up the timing light in the normal fashion and finding the mark. Get a smalll hammer and tap on the side of the engine block rapidly and if everything is working correctly you should see the timing retard 5 - 10 degrees then come back after you stop. Other mechanical issues often cause the same reaction. (rod or lifter knock to name a few)

BTW, an open or shorted knock sensor will cause a check engine light so this is strictly a double check if you are looking for issues.

Do I understand you to mean that an open or shorted knock sensor will show a fault code on my code reader? Thank you.
Find all posts by this user
Quote this message in a reply
05-13-2014, 10:45 PM
Post: #4
RE: Knock Sensor Test:
Yes, that's usually the case although depending on the year and the vehicle whatever code you get may not be specific enough to tell you open versus shorted. I have only seen a few bad knock sensors over the years and most of those are so rotten from being exposed to road salt (when mounted low) it becomes obvious it needs replacing before you can do any further testing.

Thinking back to old school theory, an open circuit may no tell you anything or set a code because the sensor generates a voltage when it hears a knock. Hard to recal the details because it's one of those things you hardly ever see even working in a shop on a daily basis.

OTOH, it was a test I used often enough back in the day because there were only a few things that caused a "brief knock" when I was at the dealer. IOW, if the knock sensor test checked ok than I would dig into the EGR system because (in that era) it was prone to clogging up. Basically the EGR not flowing (OBD-1) didn't cause a low flow code but the higher combustion temp would cause engine ping till the knock sensor could react. Typically this was a 1-2 second situation on sharp throttle jabs under load. The A-15 engine was famous for it. B-210 and 310 cars also had the issue but that was before computerized carbs in the late 80's.
Find all posts by this user
Quote this message in a reply
Post Reply 


Forum Jump:


User(s) browsing this thread: 1 Guest(s)