Knock sensor issues

[waycooljr32]

Hey all, I am getting a P0327 after replacing my ECM on my 97 Suburban with a L31 due to another issue. The replacement required reusing the knock sensor module. Can someone point me towards a flow chard for diagnosing it? The ECM was programmed by a shop locally and says that it may be an issue with the replacement ECM and wants to charge me more to diag it.

 

[AuroraGirl]

Hey all, I am getting a P0327 after replacing my ECM on my 97 Suburban with a L31 due to another issue. The replacement required reusing the knock sensor module. Can someone point me towards a flow chard for diagnosing it? The ECM was programmed by a shop locally and says that it may be an issue with the replacement ECM and wants to charge me more to diag i

i would check timing
I dont know how the 97 vortec stuff works but i imagine the computer can control the timing within a specified window and something like a bumped distributor or a procedure not followed to the letter
or a distributor that is faulty that doesnt maintain a proper situation idk just hows the timing

 

[scott2093]

Hope it's ok to jump in here.

93 Yukon been pinging, if that's the right word, recently when hitting the gas while in overdrive. Weird thing is that I did replace the knock sensor about a week ago just because it's always felt a bit gas hungry and not as peppy as I know it has been in the past.KS has never been replaced and I've never had the close call of antifreeze in the mouth so got to take care of both.
Attaching the repair tree as I followed. I'm showing Faulty prom (mem-cal) or pcm.
Any other reasons I'd get no knock sensor activity based on the repair path I took? Engine idle doesn't change when I hit block either if that matters.
Got 5v at ckt 496 if I disconnect the knock sensor. 2.4v with it connected...
had to crank the knock sensor down pretty good to get ground. Definitely more than 14ft lbs...I only tightened it til I got the ground connection showing so I could get the 3.9kohm reading

 

[Schurkey]

I am getting a P0327 after replacing my ECM on my 97 Suburban with a L31... ...Can someone point me towards a flow chard for diagnosing it?

Download the free shop manual set from the links in the sticky section of the Engine web page.

93 Yukon been pinging... ... I did replace the knock sensor about a week ago
Attaching the repair tree as I followed. I'm showing Faulty prom (mem-cal) or pcm.
Any other reasons I'd get no knock sensor activity based on the repair path I took? Engine idle doesn't change when I hit block either if that matters.
Got 5v at ckt 496 if I disconnect the knock sensor. 2.4v with it connected...

High resistance in CKT 496...maybe? Lots of voltage drop when the knock sensor is connected?

Are you measuring voltage at the knock sensor end, or at the computer end of the wire? Instructions say to measure it at the computer end.

had to crank the knock sensor down pretty good to get ground. Definitely more than 14ft lbs...I only tightened it til I got the ground connection showing so I could get the 3.9kohm reading

What did you use for sealer on the knock sensor?

Was the hole in the block rusty? Did you clean the rust out of the threads?

 

[scott2093]

High resistance in CKT 496...maybe? Lots of voltage drop when the knock sensor is connected?

No, I don't think so. It's supposed to be that way with the 5v being supplied by pcm then gets dropped to around 2.5v once knock sensor is connected because of it's resistance.

Are you measuring voltage at the knock sensor end, or at the computer end of the wire? Instructions say to measure it at the computer end.

Computer end

What did you use for sealer on the knock sensor?

Nothing. The new delco sensor looked like it had some on the threads already..like the pic

Was the hole in the block rusty? Did you clean the rust out of the threads?

Probably. I didn't clean it out.. I was thinking that too. I watched a youtube video to get an idea of any difficulties and it failed to mention there would be antifreeze pissing out so, I was in a fight trying to get the new one threaded and contain the antifreeze as fast as I could. Really should have cleaned the hole.
You don't think that because I had to crank down on it so much to get it to ground that it wouldn't register a knock? Kinda hard to get at the sensor so I'd say I gave it some light taps as well as hitting the intake and block a little harder where I could. Not too hard but enough to make me nervous

Maybe scanner isn't picking knocks up? But it seems to work on everything else. Guess I could watch the timing and see if it retards? Just to be sure. Even though I'd thought there would be some kind of rpm change or something able to be heard..

 

[L31MaxExpress]

PCM is not going to show knock retard at idle, but an oscilloscope should respond to taps.

 

[scott2093]

PCM is not going to show knock retard at idle, but an oscilloscope should respond to taps.

The old Taskmaster I have has an oscilloscope of sorts on the data streams when testing individual circuits but it didn't respond either. Guessing that gets info from pcm via aldl
How would you hook a scope up? Wouldn't that come from pcm or would I have to splice into the ks connector?
I mean, I have a regular Tektronix scope but wouldn't want to have to bring that out.

I guess I should be able to just test the ks since it's grounded in the block by seeing if it produces a voltage just to rule that out?

Should I be able to see that knock voltage at the pcm on top of the 2.5v if I reconnect and try?
Guess that's an easy thing to check.

 

[Schurkey]

Computer end

Good.

Nothing. The new delco sensor looked like it had some on the threads already..like the pic

Also good.

Probably. I didn't clean it out.

Well...you've got continuity through the sensor, so "I guess" not cleaning the threads in the block is not a big deal.

I watched a youtube video to get an idea of any difficulties and it failed to mention there would be antifreeze pissing out

Unless there's debris in the hole, or the radiator cap is still tight...the coolant should have been GUSHING out of that hole.

You don't think that because I had to crank down on it so much to get it to ground that it wouldn't register a knock? Kinda hard to get at the sensor so I'd say I gave it some light taps as well as hitting the intake and block a little harder where I could. Not too hard but enough to make me nervous

Over-tight generally makes the sensor MORE sensitive. But if it was tightened enough to cause some kind of internal damage...maybe it doesn't work any more. Or maybe it was defective to begin with.

Maybe scanner isn't picking knocks up? But it seems to work on everything else. Guess I could watch the timing and see if it retards? Just to be sure. Even though I'd thought there would be some kind of rpm change or something able to be heard..

I'd have expected the RPM to drop due to timing retard, when you tappety-tap-tap on the head or intake manifold. But see below.

PCM is not going to show knock retard at idle, but an oscilloscope should respond to taps.

Not what I'd expected...but you're the expert, and my Vortec experience is very limited.

 

[L31MaxExpress]

Good.


Also good.


Well...you've got continuity through the sensor, so "I guess" not cleaning the threads in the block is not a big deal.


Unless there's debris in the hole, or the radiator cap is still tight...the coolant should have been GUSHING out of that hole.


Over-tight generally makes the sensor MORE sensitive. But if it was tightened enough to cause some kind of internal damage...maybe it doesn't work any more. Or maybe it was defective to begin with.


I'd have expected the RPM to drop due to timing retard, when you tappety-tap-tap on the head or intake manifold. But see below.


Not what I'd expected...but you're the expert, and my Vortec experience is very limited.

The knock retard is not active until the engine is under load and at an rpm higher than idle. I would have to pull a L31 stock tune to see where it enables, but from memory it is around 55 kpa MAP and 1,200 rpm.

 

[Road Trip]

The old Taskmaster I have has an oscilloscope of sorts on the data streams when testing individual circuits but it didn't respond either. Guessing that gets info from pcm via aldl
How would you hook a scope up? Wouldn't that come from pcm or would I have to splice into the ks connector?
I mean, I have a regular Tektronix scope but wouldn't want to have to bring that out.

I guess I should be able to just test the ks since it's grounded in the block by seeing if it produces a voltage just to rule that out?

Should I be able to see that knock voltage at the pcm on top of the 2.5v if I reconnect and try?
Guess that's an easy thing to check.

Don't hesitate to take the mystery out of the circuit. Here's some firsthand experience
verifying that a new knock sensor was working after installation, and I used my old
Tek 475 to do it:

xc_hide_links_from_guests_guests_error_hide_media

IF you have the analog signal, then it's just a matter of following it upstream. And if
it makes it to the black box OK then listen to the talent in here about how the computer
is set up to make use of this input, and when. Keep us posted, this is interesting!