merchauser

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??

ammonman

Were you able to properly torque the new micro encapsulated retaining bolt for the sensor?

merchauser

I hand tightened that bolt....mistake??? also, not familiar with the micro encapsulated part??? I reused the original bolt.

FredR

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.

merchauser

with the water bridge and oil filler neck out of the way, I was able to feel the head of the knock sensor bolt and remove. old sensor looked fine, but just thought I should replace.

Fred, not sure I understand. do you mean diff as in difference? or what is duff??

FredR

"Duff" is just another way of saying knackered or non functioning to be polite- you chaps in the States would probably use the term "goosed.[which I also like and use regularly] or "fubarred".

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].

ammonman

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.

merchauser

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!

Rob Edwards

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.

worf928

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.

merchauser

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?

Rob Edwards

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.

merchauser

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.

merchauser

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?

Marti