2004 Chevy 1500 Gen 3 light throttle pinging sound

[John5]

Hi guys,

It's been a while since I've been on here. Recently I did some repairs to the truck which consisted of knock sensors, knock sensor harness, valley pan and gasket, oil pressure sending unit, valve cover gaskets, intake manifold gasket and cleaned the fuel injectors. Before this work there was a very noticeable ping or rattle sound when accelerating and thought it was because of the faulty knock sensor. While doing this work I found that the faulty sensor was very rusty and the tip for the connector was completely broken off.

All GM parts were used and the work went very good. I did the RTV seal around the knock sensor boots as well to prevent moisture from entering. With everything there replaced, I am still getting the pinging sound under light load conditions and with the scanner connected there's no KR when the sound is present or any other time. It's happening under 2,000 rpms and throttle % around 25-35%. Above that is fine and if running WOT there's no sound either. Could this be deposits built up in the cylinders or on the valves? There's also no trouble codes anymore for the knock sensors.

[blindsquirrel]

And you verified after the repairs that the knock sensors work by tappy-tap-tapping on some part of the engine while watching KS activity in the scanner, right?

[DougO]

how tight did you tighten them? too loose or too tight and they wont work properly, I over tightened mine and they wouldn't register anything

[PRS]

Really? Genuinely surprised. I am having an issue with my KR showing 0s across the entire range despite hearing pinging under load.

[John5]

And you verified after the repairs that the knock sensors work by tappy-tap-tapping on some part of the engine while watching KS activity in the scanner, right?

Hi blindsquirrel, no I did not check them but I will do that.

Thanks

[John5]

how tight did you tighten them? too loose or too tight and they wont work properly, I over tightened mine and they wouldn't register anything

Hi DougO,

I tightened to the spec of 15 ft-lb.

[DougO]

You are going to get a known good harness and knock sensors and plug them in and tap on them.

[John5]

You are going to get a known good harness and knock sensors and plug them in and tap on them.

I threw out the old harness and knock sensors so I will just test with the new ones on the engine and see that they are reading.

[5FDP]

What fuel are you running?

If it's 87 octane just bite the bullet for 1 tank of fuel and run 91+ octane. If the noise is still there, it's something else.

[John5]

Update on this,

while running and connected to the HPT scanner there was no KR registering while using a 7/8 box end wrench and tapping on each ex manifold. Tried tapping on the valley cover which houses the knock sensors and still nothing registering on the scanner while doing so. Connected my Launch scanner to monitor KR and nothing on that either...

[blindsquirrel]

To narrow it down you need to split the system up into smaller parts.

Go to the 2-wire connector at the back of the intake, the end of the KS jumper harness. Do this from pin A to ground and then pin B to ground, to check each sensor individually:

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?

You're not looking for a specific number, just a difference between tapping and not-tapping.

screenshot.08-08-2022 14.49.53.png

If both sensors (both pins) there test OK, you need to plug the KS jumper harness back in and go to the PCM-end of the harness and do the same thing but with test leads in C1 51 to gnd & then C1 11 to gnd. If that's OK, then the only thing left, however unlikely, is the PCM. Or possibly a pin fit issue with the PCM connectors, but for that to happen for only the two KS pins is very very unlikely. Not impossible though.

All of this is ASSuming that the knock sensor settings in the tune file didn't get messed with at some point, and you have not yet posted the file for other people to put eyeballs on.

[John5]

To narrow it down you need to split the system up into smaller parts.

Go to the 2-wire connector at the back of the intake, the end of the KS jumper harness. Do this from pin A to ground and then pin B to ground, to check each sensor individually:


You're not looking for a specific number, just a difference between tapping and not-tapping.

screenshot.08-08-2022 14.49.53.png

If both sensors (both pins) there test OK, you need to plug the KS jumper harness back in and go to the PCM-end of the harness and do the same thing but with test leads in C1 51 to gnd & then C1 11 to gnd. If that's OK, then the only thing left, however unlikely, is the PCM. Or possibly a pin fit issue with the PCM connectors, but for that to happen for only the two KS pins is very very unlikely. Not impossible though.

All of this is ASSuming that the knock sensor settings in the tune file didn't get messed with at some point, and you have not yet posted the file for other people to put eyeballs on.

Tested with my multi meter but mine doesn't have 400mv only 200mv so might have to get another meter however, no reading while tapping or not.

[John5]

Here's a copy of the tune file and yes sorry, should have included that.

[blindsquirrel]

200mV scale should still be able to give a yes/no answer. Like I said, not looking for a specific value, just looking for something happening only when it's being tapped on. Maxxing-out the 200mV scale is just as good an indicator of activity as going half-scale on the 400mV setting.

On ohms scale, either pin show short to ground? Should be around 100 ohms for each sensor.


----------


This is not the cause of no-KS-activity, but it is a problem:

screenshot.09-08-2022 09.37.12.png

"[ECM] 12760 - Burst Knock Enable Delta Cyl Air Threshold vs. RPM: If this value is exceeded the VCM will remove the amount of timing specified in the Burst KR vs. RPM table"

If the engine is running, it's exceeding the limit of 0.00g/s. You want that to be a value it can never exceed if you want Burst Knock disabled, not a value it always exceeds.

[John5]

200mV scale should still be able to give a yes/no answer. Like I said, not looking for a specific value, just looking for something happening only when it's being tapped on. Maxxing-out the 200mV scale is just as good an indicator of activity as going half-scale on the 400mV setting.

On ohms scale, either pin show short to ground? Should be around 100 ohms for each sensor.


----------


This is not the cause of no-KS-activity, but it is a problem:

screenshot.09-08-2022 09.37.12.png

"[ECM] 12760 - Burst Knock Enable Delta Cyl Air Threshold vs. RPM: If this value is exceeded the VCM will remove the amount of timing specified in the Burst KR vs. RPM table"

If the engine is running, it's exceeding the limit of 0.00g/s. You want that to be a value it can never exceed if you want Burst Knock disabled, not a value it always exceeds.

I didn't get a reading at all either way, will check the ohms later. Should I change the burst knock values?

Thanks

[blindsquirrel]

If you want burst knock disabled, you should change it to a value that will make it disabled all the time. Set to 0.00g/s like that makes it enabled anytime the engine is running. If you want it to work like stock you should use stock-type values.

So if the knock sensors can't make a signal to the 2-pin connector, what else could it be? The jumper harness, or the sensors themselves. Or I guess a valley plate that's not grounded, I guess, though I don't know if that's even possible. Whatever the ultimate cause turns out to be, if the test with the meter is accurate, it's now narrowed down to something between that 2-pin connector and the engine block.

[John5]

If you want burst knock disabled, you should change it to a value that will make it disabled all the time. Set to 0.00g/s like that makes it enabled anytime the engine is running. If you want it to work like stock you should use stock-type values.

So if the knock sensors can't make a signal to the 2-pin connector, what else could it be? The jumper harness, or the sensors themselves. Or I guess a valley plate that's not grounded, I guess, though I don't know if that's even possible. Whatever the ultimate cause turns out to be, if the test with the meter is accurate, it's now narrowed down to something between that 2-pin connector and the engine block.

I?ve even started the engine with the connector disconnected, shouldn?t the check engine light illuminate? The valley plate was also replaced because the old one had some putting and the new was a genuine oem part with gasket and bolts.

[blindsquirrel]

P0327/P0332:

Conditions for Running the DTC
• DTCs P0117, P0118, or P0125 are not set.
• The engine speed is between 1,500-3,000 RPM.
• The manifold absolute pressure (Map) is less than 49 kPa.
• The engine coolant temperature (ECT) is more than 60?C (140?F).
• The throttle angle is more than 0 percent.
• The engine run time is more than 10 seconds.
• The ignition voltage is more than 10 volts.
• The minimum noise level must be learned. The minimum noise level is learned when the following conditions are met:
- The engine coolant temperature (ECT) must be greater than 60?C (140?F).
- The engine speed is between 475-975 RPM for 10 seconds.

So if all the conditions are not met, it will not run the test for those codes and DTCs will never set even with sensors unplugged.

[John5]

P0327/P0332:

Conditions for Running the DTC
? DTCs P0117, P0118, or P0125 are not set.
? The engine speed is between 1,500-3,000 RPM.
? The manifold absolute pressure (Map) is less than 49 kPa.
? The engine coolant temperature (ECT) is more than 60?C (140?F).
? The throttle angle is more than 0 percent.
? The engine run time is more than 10 seconds.
? The ignition voltage is more than 10 volts.
? The minimum noise level must be learned. The minimum noise level is learned when the following conditions are met:
- The engine coolant temperature (ECT) must be greater than 60?C (140?F).
- The engine speed is between 475-975 RPM for 10 seconds.

So if all the conditions are not met, it will not run the test for those codes and DTCs will never set even with sensors unplugged.

I did a re-write of the file (write entire) and took it out for a drive and monitoring the scanner it's pulling some timing so they must be working.

[John5]

I also put in the burst knock factory values for that write as well.. Don't recall changing them to 0 but they were.