Chasing knock retard

[Snoman002]

2009 G8 GT 6.0L L76

I have a small amount of knock showing up at low throttle positions and low load. It does not appear to show up at high throttle positions, and I'm not sure but I don't believe at higher RPM's.

The car has 85k miles and is in good repair. No real aftermarket stuff or power ladders except a solo exhaust. No change in knock before or after the exhaust was installed.

I see upwards of 6 degrees retard at times when running 87 (the factory recommendation) and @.5 to 2 degrees on 93. That leads me to believe it's a 'real' knock retard.

Any thoughts on chasing this down?

 

[Rand]

Was the car designed for 87 or 93?

Many times cars designed for 93 get "recommended 87"

because requiring premium fuel is not popular.

What fuel was it recommended for in other markets(non-usa)

 

[Snoman002]

Regular, 87, is the fuel of choice for the engine. There is a 'premium' ignition map in the computer if the ECM thinks it can push timing far enough. Note, it's not a premium fuel engine with a failsafe ignition map provided the cheap stuff was used.

 

[packerlover]

Have you tried using premium fuel? If so, did it make a difference?

 

[Snoman002]

Sorry, my comments were a bit messed up. I see upwards of 6 degrees retard on 87, and 1.5 to 2 degrees on premium (93 around here)

 

[Shannow]

The L67 boys who put in tubular exhaust manifolds (available in these vehicles in Oz) have often found that the (again, note L67, maybe not applicable for yours) manifold noise, or an exhaust leak triggers the knock sensor.

They wrap the knock sensors in header wrap so that they only "hear' what's in the block.

 

[packerlover]

Originally Posted By: Snoman002
Sorry, my comments were a bit messed up. I see upwards of 6 degrees retard on 87, and 1.5 to 2 degrees on premium (93 around here)


My bad too, I didn't read it close enough. This is beyond my expertise. Good luck though.

 

[gathermewool]

How are you monitoring this timing retard?

Is it real-time are you able to check the ECM tables?

Is it feedback knock correction or fine learned correction?

 

[mehullica]

Do you have carbon buildup on the piston tops?

 

[asand1]

Egr floing freely. I have heard of low back pressure messing with egr?

 

[Olas]

To stop the retard you must stop the knock.

Flush & refill cooling system, only use premium fuel, and if it continues buy some toluene or benzene off eBay, 100ml/gallon will do it

 

[Snoman002]

Shannow,

Interesting you say that. From the bit of reading I have done it appears the L76 is very sensitive to knock, it sounds like the L67 might be the same way. No headers on this car though.


Gathermewool,
Monitored over OBD using a Bluetooth adapter and smartphone. I usually watch in real-time, however I have probably 20 hours of logs I'm attempting to do trend analysis on. I cannot answer your last question.

As far as EGR or carbon, the LS engines don't use an EGR as far as I understand, and carbon buildup is a possibility but I'm hesitant to just go throw a can of seafoam at it in hopes it fixes it.


Olas,
Interesting to hear you recommend a cooling system flush and refill. I need to do it anyways, but I'm intrigued to hear why you recommend it for knock related issues.

 

[SwampSurvivor]

EGR issues? I fought this for the entire time I had a 2001 Taurus. It would always ping and retard the timing ... and then start pinging again.

Part throttle seemed to be the worst. Part throttle with a bit of load going up a hill it would ping. Part throttle cruising on the flat, it would always have a bit of a misfire.

Turns out the EGR wasn't working right and flowing too much through causing it to always run lean and pull timing.

 

[ls1mike]

So some LS motors starting in 2001 don't have an EGR. They don't neeed it. I can't say for sure if the G8 has one or not. It sure dosen't look like it.

So it could be carbon build up on the piston, but I doubt it.

I would start with a simple tune up. Plugs and wires, they are mostly likely due with an LS at 85,000.

Some of the LS had intake gaskets that would leak. This causes a conditon which you describe.

The intake is dry so it is an easy fix. Are you getting any codes?

And don't take this the wrong way, but you have got to be the first guy I know with a performance based LS platform that does not run perimum all the time. Do yourself a favo, run a few tanks of a qualtiy permium fuel in the car and see it that makes a differenc. Something like Shell or Chevron.

My 3/4 ton is a 6.0 and I see it pull back timing when I run 87 or a premium off brand like Arco or BP. Shell, Texaco and Chevron do not pull the timing back at all.

In the truck I generally pay 20 cents more per gallon for premium. That is $6.80 a tank. Not a big deal as I get better gas mileage so I almost break even.

 

[mk378]

They say to use regular because cars that the manufacturer specifies be filled only with premium gas get knocked in reviews and "top 10" lists because of higher perceived operating cost. But if it is knocking and retarding the timing on regular, that is your sign that it would do better on premium. And like ls1mike said, you may realize enough mpg increase when it does run the more advanced timing that offsets the higher price per gallon.

 

[Ramblejam]

Originally Posted By: ls1mike
In the truck I generally pay 20 cents more per gallon for premium. That is $6.80 a tank. Not a big deal as I get better gas mileage so I almost break even.


Put 89 in my 6.0L

Not only does it noticeably run better, but the mileage increase offsets any higher cost at the pump.

 

[Rand]

The whole point I was trying to make in my first reply (second post in thread)

was the car might not even be designed to run at 0 retard on 87

 

[Snoman002]

Originally Posted By: ls1mike
So some LS motors starting in 2001 don't have an EGR. They don't neeed it. I can't say for sure if the G8 has one or not. It sure dosen't look like it.

So it could be carbon build up on the piston, but I doubt it.

I would start with a simple tune up. Plugs and wires, they are mostly likely due with an LS at 85,000.

Some of the LS had intake gaskets that would leak. This causes a conditon which you describe.

The intake is dry so it is an easy fix. Are you getting any codes?

And don't take this the wrong way, but you have got to be the first guy I know with a performance based LS platform that does not run perimum all the time. Do yourself a favo, run a few tanks of a qualtiy permium fuel in the car and see it that makes a differenc. Something like Shell or Chevron.

My 3/4 ton is a 6.0 and I see it pull back timing when I run 87 or a premium off brand like Arco or BP. Shell, Texaco and Chevron do not pull the timing back at all.

In the truck I generally pay 20 cents more per gallon for premium. That is $6.80 a tank. Not a big deal as I get better gas mileage so I almost break even.



Plugs are NGK tr55's with ~15k on them, wires are MDS's with the same mileage.

It could be a leak, however my LTFT and STFT's are not that far off. They do show regular adjustment, + or - 8 or so, but I would expect a leak to show far worse fuel trims. And no, no codes.

As far as fuel goes, it typically sees a regular diet of 93 octane from the local Kroger store. My research has show that Kroger uses a well known fuel supplier (can't remember who) that is known for having clean fuel. Otherwise it occasional gets UDF (BP) or Shell. The knock retard appears to be consistent between 87 and 93, just to a larger degree when running 87 and that is with months of straight premium. This is infact the crux of the problem, its my understanding that the knock its seeing is preventing it from using the more advanced premium ignition map. I do usually see a small improvement in fuel economy on premium however (~1mpg) so perhaps it is advancing the timing.

In the near future it will be getting a catch can (I've already participated in THOSE arguments) and I'm thinking of switching to NGK TR6 plugs just to move them a step colder. I don't believe this engine should need a colder plug being stock, but plugs are cheap.

 

[Snoman002]

Originally Posted By: Rand
The whole point I was trying to make in my first reply (second post in thread)

was the car might not even be designed to run at 0 retard on 87


Everything I have read on this engine, be it the G8 boards, HP Tuners forums, etc, is that there should be no retard on regular (87). The 6.2 in the Camaro and the G8 GXP require premium but can operate on regular due to pulled timing, this is not the case for the L76 from my understanding. What is also concerning is it seems to only do it at low throttle, low load situations. I would expect that if it was designed for 93 there should be some retard at high throttle/rpm/load conditions and I have not seen that so far.

 

[gathermewool]

The ECM most likely will try to ADVANCE overall timing first, to the max extent possible, and then will retard timing from there. My STI would start with a dynamic advance multiplier (or ignition multiplier) less than 1.0, and then, after a couple of runs, or some time driving around normally, advance to 1.0. If DAM didn't advance to 1.0, something is wrong or the tune (if it has an aftermarket tune or mods) is extremely aggressive and inefficient.

From this point of max timing, timing would be retarded immediately in degrees of timing based on feedback from the knock sensor (feedback knock.) Sometimes this feedback knock was legit and other times it was what we called "ghost" knock, since it wasn't in a high load/RPM cell and immediately cleared itself, and was more than likely noise.

If enough feedback knock correction is applied at the same load/RPM, it will be entered into a semi-permanent learned knock retard cell, so that it will automatically be applied (timing retarded) without having the knock sensor tell it to based on feedback noise. The ECM would then try to add that timing back, but not instantly.

If enough timing was learned, DAM would be reduced to less than 1.0 and the learned knock would reset and retard timing from this now lower overall timing.

I'm not sure how the G8 ECM works, but I'd imagine that Subaru didn't come up with their knock scheme independently and that theirs isn't so different from everyone else's. With that said, what are you actually viewing when you say timing is being retarded? What is the parameter called? If it's not called something like feedback correction or learned correction, are you just comparing base timing with actual timing to determine that it's being retarded?

Fuel trim:

Hopefully when you say +/- 8% fuel trim you mean short-term. At least in my Subaru, my threshold of pain was +/- 4% long-term before I started to get concerned. When I saw >6 (upwards of 8-10 at times) long-term, it turned out I had a torn turbo inlet hose that was sucking in unmetered air.