Suspiciously Zero KR across the entire Rev range...no knock retard?

[PRS]

EDIT: I think I figured it out after watching a YouTube video.... I was logging MAP in kpa in the KR scanner graph instead of cylinder airmass. Will try again tomorrow to see if this if this is the fix.

Edit 2.... 8/3/2022: I was able to fix the graph but still logging 0's.

See attached log and tune.

I read the main things you need in the channel list to log KR are cylinder airmass and knock retard. I have both of those in the scanner. My spark table is moderately aggressive for only running 87 octane (no ethanol E0) but still, I'm seeing zero's across the entire rev range.

Am I missing something easy here?cruise control test.hplMAF Tuning 1.0.hptno KR.JPG

[PRS]

Wanted to bump this thread and update the original post.

I still haven't figured out why i'm logging 0's across the board. I can hear detonation but am logging 0's. I thought I had the fix above, but I can't help but think I still have something amiss. Not even logging a fraction of KR...which is odd.

Here's today's scan and most recent tune file. I updated the lean spots now that I'm moving up in the RPM band a bit during MAF tuning.

[Alvin]

I didn't see any knock retard scrolling through the log either.

Its possible the sensors are bad.. When they fail they either pickup everything or nothing at all. When you replace them use a new harness, new GM sensors, and torque to spec.

[PRS]

The bugger of it, is this is a brand new build. I just did the first oil change yesterday. Brand new GM knock sensors, harness, and RTV seal job, all torqued to spec.

[blindsquirrel]

If only there were a method to test to see if the system is capable of detecting knock...

[Alvin]

The bugger of it, is this is a brand new build. I just did the first oil change yesterday. Brand new GM knock sensors, harness, and RTV seal job, all torqued to spec.

It could be a bad PCM.. Or brand new things can be bad out of the box.

[PRS]

If only there were a method to test to see if the system is capable of detecting knock...

I hear the sarcasm. Can you elaborate?

[Alvin]

I hear the sarcasm. Can you elaborate?

He might be talking about tapping on the engine with a wrench or something.. I'm not sure that would be conclusive . Could be wrong.

[PRS]

He might be talking about tapping on the engine with a wrench or something.. I'm not sure that would be conclusive . Could be wrong.

https://forum.hptuners.com/showthrea...l=1#post696170

Perhaps you're right. Problem is all I have at my disposal is a Duramax and a Jeep Cherokee. Not much for trying another set short of buying another new set of knock sensors and harness.

[blindsquirrel]

Important: Do not tap on any plastic engine components.

Set the DMM to the 400 mV AC hertz scale.
Measure the AC voltage from the signal circuit of the affected KS to a good ground with a DMM.
Tap on the engine block near the affected KS while observing the DMM.

Does the voltage change on the DMM while tapping on the engine block near the KS?

[PRS]

Thanks for that. I also just found a Youtube video that's helpful in explaining the same thing. https://youtu.be/cKTcXESPOJM

1 request - can you look at my scan log above in post #2 and make sure I'm not missing something in the scanner? I'd rather make a few clicks than pull apart the top of my engine to test and possibly replace the knock sensors.

[blindsquirrel]

Sorry, but what would you need to pull apart?

[blindsquirrel]

Um. What's up with those DTCs? Each one of those could be fairly serious and not something to ignore while you play with knock sensors.

[PRS]

Sorry, but what would you need to pull apart?

In order to remove the intake to replace the knock sensors, I have a coilover support bridge that needs to be removed. This is a custom frame 2500 truck with a solid axle conversion. Testing the knock sensors seems easy enough by just unplugging the harness and reaching back there.

Um. What's up with those DTCs? Each one of those could be fairly serious and not something to ignore while you play with knock sensors.

As mentioned above, the truck isn't factory. There are a few circuits in the powertrain harness that have been removed and/or modified. All the DTC's are known and deemed low priority for now.

[blindsquirrel]

Cam position circuit codes and 5vref codes are low priority?

[PRS]

Yes, low priority, because we know what these do and they stem from the same lack of circuitry built in a backup circuit. The engine is still running on primary control circuits. Let's stay on topic with KR.

[anniversaryss]

I see you made an EDIT nvmnd

[Tunercharged]

I used to use an analog sound meter to listen for knock while tuning distributor cam springs in ye olden days and if the knock sensors don’t pick up a light wrench smack to your exhaust manifolds or headers then something is probably amiss with the wiring. A bunch of bad potholes sets off my knock sensors just fine, when I get my tune closer I’ll reduce the sensitivity.