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Discussion Starter · #1 ·
This is how much timing I've had to pull out of my car and it's still registering knock all the time when cruising or accelerating lightly. Tune is completely stock except for all the timing i've pulled out of the high octane table -




I'm beginning to think it is false knock or an issue where the car doesn't provide enough fuel upon acceleration. Fuel trims are -3% almost everywhere, so I'm not lean. Happens no matter what the IATs are either. It can be 40 degrees out, it can be 80 degrees out.
 

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What your saying is ! If i had the GM lap top on this car or my Efilive scan tool i would see knock retard all the time on light throttle and at normal cruiseing speeds it would show knock retard and be pulling a few degrees timeing under these conditions? If i have it right i would say something is wrong with the engine.The coolant is completely full right(the over flow tank shows full level) Going by my car tuned i never see knock retard as showing on the lap top or scan tool under the above condition.Even at wot i may see slight knock retard on the first pull and none to speak over doing back to back pulls up threw the gears
 

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Last time I datalogged I had only intermittent knock.

What do you mean by "stock tune"? GM bone-stock flash, or HP/EFILive tuned? And, what sort of gasoline are you using?
 

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Mine has some false knock when on the highway lightly accelerating up a hill. It always spikes 1.9 degrees two or three times in a row with just enough time for the knock dissipate before reoccurring. Ive tried removing up to 4 degrees from that area and nothing changed. I ended up adding a degree or two of timing in that area and leaving it alone.

Thinking out loud...
Im not sure where the knock sensors are on this motor. I believe we can log knock retard based on cylinder but have never tried it as frankly, Im not sure how that works. Im used to two knock sensors in the water jackets which would detect knock but not which cylinder it is coming from. Unless.... they estimate which cylinder it came from using estimated differences in crank acceleration due to that piston firing. (sort of like how the engine tells theirs a misfire). Anyway, Perhaps if I log knock retard on each cylinder I could determine which knock sensor is picking up the false knock, from there i would have to try to determine cause.
 

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Discussion Starter · #5 ·
Mine has some false knock when on the highway lightly accelerating up a hill. It always spikes 1.9 degrees two or three times in a row with just enough time for the knock dissipate before reoccurring. Ive tried removing up to 4 degrees from that area and nothing changed. I ended up adding a degree or two of timing in that area and leaving it alone.

Thinking out loud...
Im not sure where the knock sensors are on this motor. I believe we can log knock retard based on cylinder but have never tried it as frankly, Im not sure how that works. Im used to two knock sensors in the water jackets which would detect knock but not which cylinder it is coming from. Unless.... they estimate which cylinder it came from using estimated differences in crank acceleration due to that piston firing. (sort of like how the engine tells theirs a misfire). Anyway, Perhaps if I log knock retard on each cylinder I could determine which knock sensor is picking up the false knock, from there i would have to try to determine cause.
This is exactly what happens to me. It will do 1.9KR and then decay and then happen two more times again and then not happen for a little bit. Logging per cylinder is next on my list.
 

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Discussion Starter · #6 ·
What your saying is ! If i had the GM lap top on this car or my Efilive scan tool i would see knock retard all the time on light throttle and at normal cruiseing speeds it would show knock retard and be pulling a few degrees timeing under these conditions? If i have it right i would say something is wrong with the engine.The coolant is completely full right(the over flow tank shows full level) Going by my car tuned i never see knock retard as showing on the lap top or scan tool under the above condition.Even at wot i may see slight knock retard on the first pull and none to speak over doing back to back pulls up threw the gears
I can't say everyone will see this but my car has been doing this ever since the day I got it off the dealer's lot.
 

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This is exactly what happens to me. It will do 1.9KR and then decay and then happen two more times again and then not happen for a little bit. Logging per cylinder is next on my list.
This is normal. The PCM is designed to fully optimize all available spark advance and constantly attempt to advance it further. The PCM is extremely quick and effective at detecting knock.

Because of this, there will always be knock present, even at 93 octane. It is GM's way of ensuring maximum efficiency.

Sent from AutoGuide.com App
 

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IIRC the 1.9* false knock is to get the mixture richened up so if more power is needed it's rich enough to be safe. There also may be some mechanical noises that sound like knock at certain RPM's and throttle positions that GM could not eliminate, so GM programmed the computer to react a specific way under those conditions to deal with it.
 

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Yeah. Don't log, but I can *feel* it at light throttle under acceleration.
 

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IIRC the 1.9* false knock is to get the mixture richened up so if more power is needed it's rich enough to be safe. There also may be some mechanical noises that sound like knock at certain RPM's and throttle positions that GM could not eliminate, so GM programmed the computer to react a specific way under those conditions to deal with it.
I don't know what to quote to disprove the enriching due to knock. But detonation should not change air fuel by a measurable amount. By false knock we are assuming what the knock the senors are picking up is not detonation but rather mechanical 'noise' in that sensors frequency band.


Gh0st- I would post my tune for you but it sounds like we have the same issue. I have seen your tune and the only differences are in the idle and driver pedal areas. Mine is a manual transmission car.
 

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Discussion Starter · #11 ·
I don't know what to quote to disprove the enriching due to knock. But detonation should not change air fuel by a measurable amount. By false knock we are assuming what the knock the senors are picking up is not detonation but rather mechanical 'noise' in that sensors frequency band.


Gh0st- I would post my tune for you but it sounds like we have the same issue. I have seen your tune and the only differences are in the idle and driver pedal areas. Mine is a manual transmission car.
I'll keep working on it to see if I can figure out what is going on. The chances are that it is purely mechanical noise would not shock me as these are quite noisey motors.
 

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I am still slightly confused i know it shows in the tables as your showing.But would a scan tool report constant KR.In other words is that table info just internal to the ecm and its not reported to the scan tool.
 

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xTooltipElement
Service Information




2012 Chevrolet Cruze | Cruze US/Canada Service Manual 2817 | Engine | Engine Controls/Fuel - 1.2L L2Q LDC LWD or 1.4L L2I L2N LDD LUH LUJ LUV | Description and Operation | Document ID: 2498118 [HR][/HR]
Knock Sensor System Description
Circuit/System DescriptionThe knock sensor system enables the engine control module (ECM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The ECM uses the knock sensor system to test for abnormal engine noise that may indicate detonation, also known as spark knock.
Sensor DescriptionThis knock sensor system uses one or two flat response dual-wire sensors. The sensor uses piezo-electric crystal technology that produces an alternating current (AC) voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency are dependant upon the level of knock that the knock sensor detects. The ECM receives the knock sensor signal through 2 isolated signal circuits.
If the ECM has determined that knock is present, it will retard the ignition timing to attempt to reduce the knock. The ECM is capable of controlling spark retard on an individual cylinder basis. The ECM will always try to work back to a zero compensation level, or no spark retard. knock sensor diagnostics are calibrated to detect faults with the knock sensor circuitry inside the ECM, the knock sensor wiring, or the knock sensor voltage output. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive mechanical engine noise.


© 2013 General Motors. All rights reserved.
 

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I remember back when i had kpro the k series engines did produce a lot of ghost knock. So my tuner set up the knock threshold. Anything under 2.0 was ignored by the ecm.
 

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I read your post on HPtuners Ghost.Why dont you bring that car into the dealer.Dont say anything about tuneing it.Leave it stock and ask them if they can call GM technical assistance about your condition.There may be other cases of the same type of problem.I would just say the car pings on the highway with any type of fuel in it.I am sure if a decent Tech drives in under those conditions and looks at scan data they are going to know its showing KR when it should not.It very well may have a mechanical issue valve timeing related.It could even have a piston related issue.
 

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Ghost, i have the same low load low rpm KR on 93 octane. I'm not sure the source, and even after pulling some timing (although not as much as you), it was unaffected. While it's not something to ignore, the key is at WOT/full boost, it doesn't knock. That's where major damage occurs, not really at the low loads. One experiment I did want to run is to compare a 93 octane log in those cells to an 87 octane log. If both are showing the same low load KR, I'm not going to worry about it. However, if the 87 octane makes it WAY worse in those cells, then it's an indication to me that something real is going on .
 
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Discussion Starter · #17 ·
Ghost, i have the same low load low rpm KR on 93 octane. I'm not sure the source, and even after pulling some timing (although not as much as you), it was unaffected. While it's not something to ignore, the key is at WOT/full boost, it doesn't knock. That's where major damage occurs, not really at the low loads. One experiment I did want to run is to compare a 93 octane log in those cells to an 87 octane log. If both are showing the same low load KR, I'm not going to worry about it. However, if the 87 octane makes it WAY worse in those cells, then it's an indication to me that something real is going on .
I'm back on stock timing and I'm ignoring the knock retard for now. It's a problem to me though because of the cylinder airmass vs. knock retard torque management table. I don't like fudging tables like that especially when it relies on knock retard to manage the cylinder airmass. I guess I don't need the table there as no other car I've owned has used it, but the safety catch where the car will save itself from further damage is something that is very welcome to me.
 

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This is normal. The PCM is designed to fully optimize all available spark advance and constantly attempt to advance it further. The PCM is extremely quick and effective at detecting knock.

Because of this, there will always be knock present, even at 93 octane. It is GM's way of ensuring maximum efficiency.

Sent from AutoGuide.com App
I thought it knocked because our cars don't have a flex fuel sensor so they using knock to determine the alcohol %, as more alcohol content means more knock suppression. So there should be more knock after fuel ups until it learns.

Note: I had knock at low load on the stock tune in my vehicle
 

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I thought it knocked because our cars don't have a flex fuel sensor so they using knock to determine the alcohol %, as more alcohol content means more knock suppression. So there should be more knock after fuel ups until it learns.
Yes, you can definitely feel it "testing the limits" right after a fill-up. Leaving the gas station, I'll have lots of pep and then suddenly it backs off a little bit.
 
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