Proper knock readings with hammer
#1
Three Wheelin'
Thread Starter
Proper knock readings with hammer
a few months ago I used a bosch hammer to check my car out. the knock registration showed
less than 3 during leisure runs, and averaged 30 during aggressive drives with shifts near 5500.
just replaced my oil filler and was able to reach in a replace my front knock sensor. it looked OK,
but thought I should just replace it for good measure.
car runs and feels terrific!
now, with aggressive runs, I get readings of 120 with the hammer?? any ideas??
less than 3 during leisure runs, and averaged 30 during aggressive drives with shifts near 5500.
just replaced my oil filler and was able to reach in a replace my front knock sensor. it looked OK,
but thought I should just replace it for good measure.
car runs and feels terrific!
now, with aggressive runs, I get readings of 120 with the hammer?? any ideas??
#3
Three Wheelin'
Thread Starter
Were you able to properly torque the new micro encapsulated retaining bolt for the sensor?
#4
Rennlist Member
knock events will invariably be more frequent with full load runs ues the timing is tuned to ensure such do not happen. When change a duff knock sensor out you get 6 more degrees of advance than you did previously when a duff sensor was in place and that is a night and day type of difference performance wise.
It would be useful to learn a little more about how you managed to change a knock sensor without removing the inlet manifold.
It would be useful to learn a little more about how you managed to change a knock sensor without removing the inlet manifold.
#5
Three Wheelin'
Thread Starter
It would be useful to learn a little more about how you managed to change a knock sensor without removing the inlet manifold.
When change a duff knock sensor out you get 6 more degrees of advance than you did previously when a duff sensor was in place and that is a night and day type of difference performance wise.
#6
Rennlist Member
If the water bridge and filler neck were out of the way that makes sense. Personally I reckon it is easier to pull the inlet manifold then you can get at both sensors - if one has gone the other will not be far behind it so changing out one is alien to me. I have them on my 10 year replacement schedule - just did mine a few weeks ago when I changed out the ISV for good measure as well given that it was "ancient". Doubtless you understand but if one knock sensor or the Hall trigger is non functional you lose 6 degrees of advance. Fortunately as a Sharktuner owner I simply put ST2 on the car and its diagnostic capabilities tell me whether these items are working [or not].
#7
Rennlist Member
The knock sensor bolts get 20 Nm (14.75 ft/lbs) torque. The factory replacement mounting bolts are pre-coated with thread locker (micro-encapsulated.) The thread locking compound doesn't take effect until the micro bubbles are broken during tightening. Any old removable thread locker will work but the factory replacement bolts are pre-coated.
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#8
Three Wheelin'
Thread Starter
thanks for that info mike: do you think reusing the original bolt was a mistake and my have created a problem.
the irony, is that I believe the old sensor was fine!
the irony, is that I believe the old sensor was fine!
#9
Archive Gatekeeper
Rennlist Member
Rennlist Member
If you put the new sensor with the bolt finger tight, its attachment with the block is markedly different than were it torqued down correctly. I'd venture its output signal is very different than what it would be torqued. Judging by what you're seeing it's generating a lot of spurious knocks.
#10
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A properly running 928 will show 0 knocks with the hammer no matter how you drive it. Less then 5 knocks if you're lugging it or hammering it for the whole test is acceptable but would not meet my standards.
OP - you need to bite the bullet and do a full intake refresh including both knock sensors (properly torqued), cleaned and balanced injectors, rebuilt Mass-Air sensor, etc.
Stan's told you this. I've told you this. Sean's told you this. Quit !@#$ing around and get'r done.
OP - you need to bite the bullet and do a full intake refresh including both knock sensors (properly torqued), cleaned and balanced injectors, rebuilt Mass-Air sensor, etc.
Stan's told you this. I've told you this. Sean's told you this. Quit !@#$ing around and get'r done.
#11
Three Wheelin'
Thread Starter
can someone give me an idea how I can test the knock sensor with an ohm meter? readings expected?
I am thinking that there was nothing wrong with my old one, and that I either overtighten the new one or
its too loose.
it there a way to test the old one I have on the bench? compare readings?
I am thinking that there was nothing wrong with my old one, and that I either overtighten the new one or
its too loose.
it there a way to test the old one I have on the bench? compare readings?
#12
Archive Gatekeeper
Rennlist Member
Rennlist Member
Knock sensors are microphones- You'd need an oscilloscope and a frequency generator to be able to look at the waveform generated. I've not seen a test protocol for our particular knock sensors, though there are some for other similar looking Bosch sensors scattered around the internet. The new sensor you installed is likely just fine. In lieu of the intake removal we're advocating for, at the very least you should re-pull the filler neck and torque the sensor bolt properly.
#13
Three Wheelin'
Thread Starter
Thanks Rob. and to all those with the best intentions, I hear the admonishments and understand. MY problem, is that I am working on 5 projects at the
same time, and unfortunately, the 928 is at the very bottom. very close to completion of a 3 year restoration of one car, and lots of other work on the others.
so, with that in mind, I am doing my very best to use this car, when I can, and have some good fun. when I take the intake out, I want to be able to focus on ALL
necessary bits needing replacement, and that time is a year away.
Rob and community: do you think that I have the sensor bolt is too loose or too tight? (my gut suggests that it is too loose, and bouncing around?)
and if too tight, is it possible that I damaged the sensor. assuming if the sensor was damaged, I would get a fault code with the hammer? no fault codes to report.
is a good idea to replace with a fresh OEM bolt?
I can do that, if needed. I was just hoping there was some way to ohm test the new one and the old one and compare. would
like some feedback on whether I "can" just retorque, or will "need" to replace.
FWIW: on my first attempt to tighten the sensor bolt, I quickly found that some crud has gotten into the hole and the bolt
would not go all the way down. (sensor was loose) pulled out the bolt, blew out the hole, and bolt went all the way down.
same time, and unfortunately, the 928 is at the very bottom. very close to completion of a 3 year restoration of one car, and lots of other work on the others.
so, with that in mind, I am doing my very best to use this car, when I can, and have some good fun. when I take the intake out, I want to be able to focus on ALL
necessary bits needing replacement, and that time is a year away.
Rob and community: do you think that I have the sensor bolt is too loose or too tight? (my gut suggests that it is too loose, and bouncing around?)
and if too tight, is it possible that I damaged the sensor. assuming if the sensor was damaged, I would get a fault code with the hammer? no fault codes to report.
The knock sensor bolts get 20 Nm (14.75 ft/lbs) torque. The factory replacement mounting bolts are pre-coated with thread locker (micro-encapsulated.) The thread locking compound doesn't take effect until the micro bubbles are broken during tightening. Any old removable thread locker will work but the factory replacement bolts are pre-coated.
you should re-pull the filler neck and torque the sensor bolt properly
like some feedback on whether I "can" just retorque, or will "need" to replace.
FWIW: on my first attempt to tighten the sensor bolt, I quickly found that some crud has gotten into the hole and the bolt
would not go all the way down. (sensor was loose) pulled out the bolt, blew out the hole, and bolt went all the way down.
#14
Three Wheelin'
Thread Starter
Update and new questions:
I have replaced both knock sensors (proper torques and new OEM bolts), hall sensor, CPS sensor,
temp ll sensor, among other bits. there are no fault codes and car idles great. made some runs and knock
registration with the hammer were, 128, 98, and 85.
would all agree that those numbers are insane, and IF truly accurate, indicate a real problem?
fast forward. beginning to realize that my motor mounts are collapsed. I am thinking (and hoping), that all
those knocks are because of the motor mounts?? anyone else have this issue?
I have replaced both knock sensors (proper torques and new OEM bolts), hall sensor, CPS sensor,
temp ll sensor, among other bits. there are no fault codes and car idles great. made some runs and knock
registration with the hammer were, 128, 98, and 85.
would all agree that those numbers are insane, and IF truly accurate, indicate a real problem?
fast forward. beginning to realize that my motor mounts are collapsed. I am thinking (and hoping), that all
those knocks are because of the motor mounts?? anyone else have this issue?
#15
Pro
I doubt the engine mounts situation would cause additional knocks.
I think its it’s more likely you are experiencing some level of lean fuelling due to MAF, air leak, bad/dirty injector/s. The AFR doesn’t need to drop off much in the mid range to bump up the knock count.
I would say that the number is pointing towards AFR problem. The engine could be ingesting oil during these runs which could be bumping up the knock count. I would suggest installing a baffle under the oil filler if you have not already done so to remove that problem, it completely cleans the inlet manifold up of oil.
Unfortunately this is all manifold off work however this is much easier than it looks once you research the job and have a decent tool kit available.
I think its it’s more likely you are experiencing some level of lean fuelling due to MAF, air leak, bad/dirty injector/s. The AFR doesn’t need to drop off much in the mid range to bump up the knock count.
I would say that the number is pointing towards AFR problem. The engine could be ingesting oil during these runs which could be bumping up the knock count. I would suggest installing a baffle under the oil filler if you have not already done so to remove that problem, it completely cleans the inlet manifold up of oil.
Unfortunately this is all manifold off work however this is much easier than it looks once you research the job and have a decent tool kit available.