Knock sensor issues

[Road Trip]

Hi Scott,

I've been doing some research on your problem, and happened across the following
customer feedback re: new AC Delco knock sensor:

You must be registered for see images attach

This sure sounds similar to what you have been going through? Thoughts?

 

[scott2093]

Wow..
Say it ain't so...
What's weird..or not... is that a couple of sellers on feebay have some original AC Delcos in boxes and it looks like the part numbers are stamped in the metal case. These last 2 I got just have stickers....

 

[Road Trip]

So I just ordered another knock sensor from the same Amazon AC Delco store because nobody locally can get one to satiate my impatience afaik, didn't want to wait for Summit and I need to get going to work. It'll be here Monday hopefully. At least it's reviews are better..almost perfect...

Scott,

Thinking further about your situation, I went back to this comment.

I'm wondering if they are the only one with any stock in hand, does this
mean that they got somehow got ahold of a bad batch, and you
have received 2 bad sensors. Given my previous post of another
AC Delco customer last summer who also had 2 new sensors that
didn't generate a voltage, but the old rusty sensor was working, validating
their test methods?

****

By the way, rereading your comments you are using a scan tool or multimeter
to make your readings? I would be cautious, because a lot of times an AC meter
will work at normal line frequency (50, 60 hz) and sometimes aircraft AC power
(400hz) ...but not up in the 5-7 Khz range that these resonant knock sensors
operate. And normally they display the results in RMS (root mean square,
or effective power) which is going to be different that a pk-pk display on the
scope. (By the way, you might be a EE for all I know, not trying to talk down
to you at all, just covering the bases so that we are on the same page.)

****

Just read your latest -- hope you aren't being fed counterfeits. :-(

 

[Road Trip]

Listen, hopefully some of the parts gurus will jump in here and share their
wisdom regarding stamped vs. stickered parts.

You know, if the parts you found on ebay are NOS (New Old Stock) that
might be the fix for this situation. (An old part made to OEM specs that's
never been used, and still in the original box.)

For what it's worth, I've seen NOS parts work where newer stuff wouldn't.
But I'm hoping that the parts gurus in here can share their perspective...

 

[scott2093]

I'm wondering if they are the only one with any stock in hand, does this
mean that they got somehow got ahold of a bad batch, and you
have received 2 bad sensors.

!st order came from Summit Racing. The second one I got from Amazon. AC Delco store. Both came in GM bags. You'd think they would be packaged a little better. Summit was good obviously but Amazon just came in a padded envelope.

By the way, rereading your comments you are using a scan tool or multimeter
to make your readings? I would be cautious, because a lot of times an AC meter
will work at normal line frequency (50, 60 hz) and sometimes aircraft AC power
(400hz) ...but not up in the 5-7 Khz range that these resonant knock sensors
operate. And normally they display the results in RMS (root mean square,
or effective power) which is going to be different that a pk-pk display on the
scope

Yes I wondering about that and why I mentioned my meter was rms. It's a Fluke 8060A and although I know the specs are impressive, I haven't considered the frequency and was more focused on the level ...good point. No, not an ee by any stretch...lol I've used my Tek 2225 a total of 4 times in the 7 years I've had it. Seeing gnat farts just leads me down to depths I'm not prepared for usually....but it's been the right tool when it had to be for sure.

edit/// from 8060a manual
"True rms measurements for ac signals up to 100 kHz."

Yeah I have no issues with nos parts and have been lucky in the past. I sometimes wonder if big stores can get the white truck specials. I bought a pair of headphones many years ago from a huge retailer and they were clearly fake. Not sure if it was an inside store thing going on or something else...
Sucks
It'll get figured out... It's hard to believe that 2 in a row from different places, although from the same I guess, would be the same. Making me think of other scenarios for sure..

 

[Road Trip]

Your situation kind of reminds me when we would get 2 or 3 of the same new part that wouldn't
work for us on aircraft. It should have fixed the write up, but didn't. In these special cases, we
would cannibalize a 'known good, flown good' part from another jet, and sure enough, now the first
jet would start working as expected. To verify, we would take one of the new/suspect parts, run
it in the Cann'd jet, and it would fail. I would then initiate a QDR. (Quality Deficiency Report.)

And eventually we would find out that a new supplier had come online...and they were having issues
with their stuff.

****

Of course, you probably don't have the luxury of a known good vehicle with the same engine in it
so that we could Cann(ibalize) the knock sensor and verify that the rest of the Knock Sensor circuitry
is good in your truck? :0)

****

Regarding your Tek 2245. I went down the TI white paper (rabbit hole**) you linked to. And on p. 16
they discussed whether you would need an 8 or 10-bit A/D converter in order to have enough resolution
to handle the total signal from the knock sensor:

You must be registered for see images attach

So, this validates the 6V pk/pk signals I was seeing with my old Tek 475 while tapping on that engine block. (And that
old scope has a good track record -- I spelunk with it inside audio amps on occasion.)

At this point, I don't know.
* Go to the treasure yard and pull two or three good looking ones from identical engines for a song? Bring them
home, thread them into your block, (not vise) connect up your 2245, and see if you can get a similar output to the video?
* Buddy has an engine on a stand, and won't be needing his sensor for a short while?
* Find a NOS sensor?
* Or maybe someone in here can recommend a different brand that's been working for them recently?

Keep us in the loop -- thanks!

**(See attached.)

 

[scott2093]

Go to the treasure yard and pull two or three good looking ones for a song? Bring them
home, thread them into your block, (not vise) connect up your 2245, and see if you can get a similar output to the video?

hmmm. Thought never crossed my mind. At this point it's looking pretty good actually.

The Fluke 8060a meter says true rms signals up to 100khz... This should mean it is picking up something? It even has hz so I think I should be able to see the frequency but idk...Would have to look if it displays that low of a level....or in the khz range.. I think so...

But yeah, something needs to be done. A return to Amazon being one....
Thank you for your help!
This path sure didn't go as I had pictured it but it's great alzheimer's prevention I'm hoping if nothing else...

 

[Road Trip]

hmmm. Thought never crossed my mind. At this point it's looking pretty good actually.

The Fluke 8060a meter says true rms signals up to 100khz... This should mean it is picking up something? It even has hz so I think I should be able to see the frequency but idk...Would have to look if it displays that low of a level....or in the khz range.. I think so...

But yeah, something needs to be done. A return to Amazon being one....
Thank you for your help!
This path sure didn't go as I had pictured it but it's great alzheimer's prevention I'm hoping if nothing else...

I saw your edit -- 100Khz is pretty impressive for a DVM -- Fluke is definitely professional strength stuff.

You know, recently I dug my Tek 475 out of deep storage, but haven't plugged it in yet. Been reading around,
and it seems that it would be prudent to replace the electrolytic caps in it before I power it up. (Or better,
bring it up slowly on a Variac I have.) The scope has never given me any trouble, but electrolytics have a
finite service life, and I would be a jerk to damage a fine piece of analog test gear because I couldn't trouble
myself to do some prudent preventive maintenance first. But someday soon I hope to be able to share a quality
scope display of my 7.4L knock sensors. All in the effort to help remove the mystery surrounding these engine block
microphones.

Man, not only am I old...but so is my test equipment. :0)

 

[scott2093]

You know, recently I dug my Tek 475 out of deep storage, but haven't plugged it in yet. Been reading around,
and it seems that it would be prudent to replace the electrolytic caps in it before I power it up.

Yeah it's one of the first things I did to mine. Respect for the crt is in order for sure.
I am stupid and just fire things right up with the standard half turn, cringed in ready to unplug or run position. Don't recommend.
My scope was a bit goofy in some functions and caps are always low hanging fruit that reward victory often in my experience...this was no different. Wow...Tant city in yours...

 

[scott2093]

Whitesnake playing in background...

A seller took my best offer on his nos ks...we'll see....

Actually waiting on a call back from AC Delco hardware support. Figured it can't hurt to see if any info, testing or otherwise, can be dug up before I send this 2nd one back. Already spent time on phone with their software side of support to rule out maybe some other issues with other sensors or whatever....

Feel kinda bad wasting other people's time with such a small, outdated thing. Feels like going to Ace Hardware and having the guy there help me for 15 minutes to find a couple of obscure screws... their screws are pretty pricey though..lol