After a bazzillion threads on this board of knock happening here or there, I want to make a thread to help those looking for solutions.
First, read this paragraph twice... Your knock sensor is basically a microphone that is located on the rear of the engine block. It is connected to an ESC module that "filters" out specific frequencies that are metallic sounding. Depending on the severity/intensity of this sound.. will vary the output of the ESC module. Your vehicle's computer picks up this information and displays the knock readings. This is why knock detectors will show knock before it is displayed on your scan tool. This is becuase knock detectors are connected directly to the output of the ESC module. Some chips have the ability to "mask" out the knock readings under certain conditions.. this is also known as "knock ignore". Example the Extender when you downshift.. it ignores knock for a predetermined amount of time.
Now here comes the kicker. Real knock escalates in intensity. It will increase in severity. Call it avalanche.. the little pebble that turns into the huge snowball. And monitoring knock on scantools your to look at numbers and severity that increase. Example 1, 3, 7, 11, 20... kaboom. Numbers that flash all of a sudden "20".. is false. Just as numbers that come then disappear. The only thing is if your on the edge of knocking.. numbers will hover in the very low digits coming and going. Like 0, 0, .5, 0, .7, 0.. etc. This means your on the edge and need to make a tuning change(timing/octane/fueling). I'll get into this latter.
So is it real or false? Hopefully re-read the above until it sinks in.
Now.. if your still in doubt ask your self the following questions.
1) Is the boost set at a level that the motor should not knock based on fuel octane? Pump gas 91-93 octane should get you typically 12-14 PSI boost with a normally functioning engine. Note I use the word "typically". Some may get 24 PSI.. Just like some win the lottery
2) Is the chip working properly and matched to the injectors used? If your not 100% sure on this question.. stop and buy a chip from someone reputable. Period. Stop wasting your time and the time of others trying to get an unknown chip with unknown injectors to properly sync together. If your chip is matched to the injectors, make sure fuel pressure is set correctly and BLM numbers are within normal ranges. I'll get into BLM latter in tuning.
3) If your boost is low, your octane is premium, you have a matched chip for your injectors, all scantool numbers are withing normal limits, engine idles quiet, stays quiet when you rev it, you should not be experiencing any "REAL" knock. Assuming your engine doesnt have a blown headgasket, huge leakdown, wiped out cam, etc. Easily confirmed with leakdown and compression tests.
4) At low boost your motor should not knock. Unless something internally is coming apart. I can pretty much make this a blanket statement. Just like it shouldnt knock when rev'ing in park/neutral.
So far so good.. so you followed the above and still see the lights and numbers climbing on your scantool...
Lets take it one step further.. There are way too many conditions that can create knock readings. There are certain conditions that aggravate trying to ascertain whether its real or false. I typically when working on this issue try and limit certain scenario's. The number 1 scenario is trying to do a boosted launch on a street surface then seeing the numbers climb. What this means is slamming the pedal down in first gear and spinning tires in hopes to get real data. My suggestion is to perform this test in manual 2nd gear or manual 3rd. Whereby the car cannot spin tires or "shift" gears. And then ease into the throttle watching the boost guage climb while paying attention to knock readings. If the boost guage climbs slow to the preset boost level and the knock readings dont appear.. you have your answer. SO if you set to 14 PSI and it runs with zero on the knock readings your chasing false knock.
There are some scenario's whereby all the idle and drivability would appear to be normal.. and the car will start showing knock as it goes into boost. Example is bad mass air flow sensor(MAF).. whereby it doesnt read the airflow correctly and an improper amount of fuel is sent into the engine. This is typical with remanufactured MAF's sensors. And only way to ascertain is by either swapping for a known good piece, or watching air fuel readings on a wide band sensor. If the car leans out as it goes into boost.. it can/will knock.
Another is a bad O2 sensor whereby your fuel settings are "learned" improperly. That is why I always preach the use of GM pieces in your Buick. There is nothing wrong with an AFS20 single wire O2 sensor.
Now.. lets see if we can figure out where the metallic noise is coming from. This would be to address false knock issues.
So.. you've lowered boost.. assured proper octane.. car is running slightly rich.. chip and injectors are matched.. all plugs look even and light brown/tan.. gets great gas mileage.. no drivability issues coming from stops.. etc..
Lastly.. 3 degree's of sustained knock is not severe. You will not blow your engine up at low boost with 3 degree's showing. Anything under 15 PSI..probably can sustain 8-10 degree's for a pretty long time.
If you see .1 knock.. the sky is not falling. I have seen multiple times whereby someone see's .5 degree's and lifts screaming... ohh noo .
And if your hearing the "marbles in a can" type of sounding when putting a load on your engine.. aka.. pinging.. YOU BETTER LIFT OR ELSE>>>
Lets work on deciphering the flase knock..
The best thing to do is make a list of what can create this and work down the list. Crossing off what is and isnt.
And you need to be able and replicate the condition without undo stress on the motor. Putting the engine at 25 PSI is foolish looking for a problem.
So we get back to the microphone listening to the engine.
The following is a list of possibilities.. and there can be even more.. but this should cover the majority.
Engine mounts, downpipe clearance, TQ converter bolts loose, pulley/tensioner problems, wrong knock sensor(microphone), wrong/bad ESC module, wire harness banging on knock sensor, bad timing chain, bad rocker shafts, noisy lifters, bad thrust on crank, transmission pump, bent pushrod, bad bearing, bad piston/wrist pin, MAF pipe hitting alternator, alternator, power steering pump, etc.. hope you see the complexity and time involved in diagnosing this type of issue.
First, read this paragraph twice... Your knock sensor is basically a microphone that is located on the rear of the engine block. It is connected to an ESC module that "filters" out specific frequencies that are metallic sounding. Depending on the severity/intensity of this sound.. will vary the output of the ESC module. Your vehicle's computer picks up this information and displays the knock readings. This is why knock detectors will show knock before it is displayed on your scan tool. This is becuase knock detectors are connected directly to the output of the ESC module. Some chips have the ability to "mask" out the knock readings under certain conditions.. this is also known as "knock ignore". Example the Extender when you downshift.. it ignores knock for a predetermined amount of time.
Now here comes the kicker. Real knock escalates in intensity. It will increase in severity. Call it avalanche.. the little pebble that turns into the huge snowball. And monitoring knock on scantools your to look at numbers and severity that increase. Example 1, 3, 7, 11, 20... kaboom. Numbers that flash all of a sudden "20".. is false. Just as numbers that come then disappear. The only thing is if your on the edge of knocking.. numbers will hover in the very low digits coming and going. Like 0, 0, .5, 0, .7, 0.. etc. This means your on the edge and need to make a tuning change(timing/octane/fueling). I'll get into this latter.
So is it real or false? Hopefully re-read the above until it sinks in.
Now.. if your still in doubt ask your self the following questions.
1) Is the boost set at a level that the motor should not knock based on fuel octane? Pump gas 91-93 octane should get you typically 12-14 PSI boost with a normally functioning engine. Note I use the word "typically". Some may get 24 PSI.. Just like some win the lottery
2) Is the chip working properly and matched to the injectors used? If your not 100% sure on this question.. stop and buy a chip from someone reputable. Period. Stop wasting your time and the time of others trying to get an unknown chip with unknown injectors to properly sync together. If your chip is matched to the injectors, make sure fuel pressure is set correctly and BLM numbers are within normal ranges. I'll get into BLM latter in tuning.
3) If your boost is low, your octane is premium, you have a matched chip for your injectors, all scantool numbers are withing normal limits, engine idles quiet, stays quiet when you rev it, you should not be experiencing any "REAL" knock. Assuming your engine doesnt have a blown headgasket, huge leakdown, wiped out cam, etc. Easily confirmed with leakdown and compression tests.
4) At low boost your motor should not knock. Unless something internally is coming apart. I can pretty much make this a blanket statement. Just like it shouldnt knock when rev'ing in park/neutral.
So far so good.. so you followed the above and still see the lights and numbers climbing on your scantool...
Lets take it one step further.. There are way too many conditions that can create knock readings. There are certain conditions that aggravate trying to ascertain whether its real or false. I typically when working on this issue try and limit certain scenario's. The number 1 scenario is trying to do a boosted launch on a street surface then seeing the numbers climb. What this means is slamming the pedal down in first gear and spinning tires in hopes to get real data. My suggestion is to perform this test in manual 2nd gear or manual 3rd. Whereby the car cannot spin tires or "shift" gears. And then ease into the throttle watching the boost guage climb while paying attention to knock readings. If the boost guage climbs slow to the preset boost level and the knock readings dont appear.. you have your answer. SO if you set to 14 PSI and it runs with zero on the knock readings your chasing false knock.
There are some scenario's whereby all the idle and drivability would appear to be normal.. and the car will start showing knock as it goes into boost. Example is bad mass air flow sensor(MAF).. whereby it doesnt read the airflow correctly and an improper amount of fuel is sent into the engine. This is typical with remanufactured MAF's sensors. And only way to ascertain is by either swapping for a known good piece, or watching air fuel readings on a wide band sensor. If the car leans out as it goes into boost.. it can/will knock.
Another is a bad O2 sensor whereby your fuel settings are "learned" improperly. That is why I always preach the use of GM pieces in your Buick. There is nothing wrong with an AFS20 single wire O2 sensor.
Now.. lets see if we can figure out where the metallic noise is coming from. This would be to address false knock issues.
So.. you've lowered boost.. assured proper octane.. car is running slightly rich.. chip and injectors are matched.. all plugs look even and light brown/tan.. gets great gas mileage.. no drivability issues coming from stops.. etc..
Lastly.. 3 degree's of sustained knock is not severe. You will not blow your engine up at low boost with 3 degree's showing. Anything under 15 PSI..probably can sustain 8-10 degree's for a pretty long time.
If you see .1 knock.. the sky is not falling. I have seen multiple times whereby someone see's .5 degree's and lifts screaming... ohh noo
.And if your hearing the "marbles in a can" type of sounding when putting a load on your engine.. aka.. pinging.. YOU BETTER LIFT OR ELSE>>>
Lets work on deciphering the flase knock..
The best thing to do is make a list of what can create this and work down the list. Crossing off what is and isnt.
And you need to be able and replicate the condition without undo stress on the motor. Putting the engine at 25 PSI is foolish looking for a problem.
So we get back to the microphone listening to the engine.
The following is a list of possibilities.. and there can be even more.. but this should cover the majority.
Engine mounts, downpipe clearance, TQ converter bolts loose, pulley/tensioner problems, wrong knock sensor(microphone), wrong/bad ESC module, wire harness banging on knock sensor, bad timing chain, bad rocker shafts, noisy lifters, bad thrust on crank, transmission pump, bent pushrod, bad bearing, bad piston/wrist pin, MAF pipe hitting alternator, alternator, power steering pump, etc.. hope you see the complexity and time involved in diagnosing this type of issue.
