Ok, here is the low down. I have 2006 Chevy Silverado 4.8l with a sts turbo kit with upgraded injectors and only pushing 5psi. I have had the kit on the truck for about 2 years now with no problems. Tonight on my way to my brothers house from work I hooked up the scan tool to monitor my truck. While cruising down the free way I was keeping a eye on the scan tool, boost gauge, and wide band gauge. I give the truck some boost and everything seems normal. No bad o2 readings, no over boost, and no knock. As I get down a little further down the road I see the knock reading move up .50-1.00kr and this was not under any boost. Right then I am thinking maybe false knock. So I give it some boost, maybe half throttle and see nothing on the knock reading. So now, I am certain it is false knock. Well as I progress down the free way this time under more boost I see the kr reading hit 2.10 with a good o2 reading from the wideband. Now I know this can't be false and I have a problem. Throught out the ride to my brothers I kept it out of boost and saw no knock. Well on the way back to my house I would play around with a little boost to make sure I was not getting any false readings. So every so often I will give the truck boost but not under any wide open blasts. Some times I would see little knock on a pass maybe .20- 1.12kr and other times I would see nothing. So my question is am I seeing false knock? Is there any way for me to determain that this is a false reading? Any info to shed some light on the subject would be great.
Not a Buick but maybe I can still get some help
- Thread starter TwinyTwin
- Start date
From what you are describing it could be real knock and in my opinion 2.0 or less is really nothing to worry about.
Does the knock increase as you accelerate?
If it stays in the 2.0 and under range I would suspect some bad gas......what fuel do you use...regular pump gas?
Does the knock increase as you accelerate?
If it stays in the 2.0 and under range I would suspect some bad gas......what fuel do you use...regular pump gas?
I am running 93 octane.
This morning I saw 3.25kr on my scan tool this morning with no boost and did not see kr when I was under boost at 1/2 throttle. I was wondering if this cold weather has any effect on the kr? My truck was tuned in the middle of the summer with 93 degree heat. Lately its been in the low 30 in the morning and evening.
I have a MSD fuel pump boost moduel laying in my garage and was going to throw it on the truck when I get off work. Do you think this could help out? I just might have to take it back to the dyno and get a retune. I also sent Julio at alkycontrol a email for pricing on a alky kit. I just may end up going this route and get retune with more boost
.
This morning I saw 3.25kr on my scan tool this morning with no boost and did not see kr when I was under boost at 1/2 throttle. I was wondering if this cold weather has any effect on the kr? My truck was tuned in the middle of the summer with 93 degree heat. Lately its been in the low 30 in the morning and evening.
I have a MSD fuel pump boost moduel laying in my garage and was going to throw it on the truck when I get off work. Do you think this could help out? I just might have to take it back to the dyno and get a retune. I also sent Julio at alkycontrol a email for pricing on a alky kit. I just may end up going this route and get retune with more boost
.yes I would say it is definitely possible the cold weather could be effecting the performance on the low side especially since it was tuned when it was hot out. Cold weather is more dense than hot so the increase in air charge and not enough fuel at low rpm and load could cause what you are having. The fix may be a re-tune to increase injector pulse width but then you may have a little rich condition in the summer.
Better to be a little on the rich side than lean I always say.
Better to be a little on the rich side than lean I always say.
do you have a boost gauge? Like the other dude said, the colder denser air will increase boost a few psi. You might be at 7psi or so. Have you ran a wot blast? If you have no knock at wot, I would not be concerned. Especially with only around 2.0 knock. You'll get that if you fart in your seat hard enough, just dont leave a skid mark.
machinegun
Active Member
- Joined
- May 25, 2001
There are couple of items I think we need to mention and possbily look at.
Your 4.8l knock sensors is much more sensitive than a GN. There should be 2 knock sensors and these go into water jackets rather than block. One reason is that the coolant will actually transfer sound much better than cast iron or aluminum.
Massive changes in temperature can drastically change the way an ECM is controlling timing and fuel curves especailly since the tunning was done in the summer. The ECM bases a lot of its cold start run fuel and timing parameters off of the engine temp sensor not so much the MAT. IE the same fule and timing maps are being used even though there is colder denser air in the combustion chamber.
Another item is the formulation of fuel. Colder weather is usually associated with differnt formultations of fuel for cold weather. These can be additives to prevent freezing, and other components.
My recommendation would be to either get it retuned for cold weather and winter formulated fuel or just be careful mindful and a little easier on it.
The amount of knock you are telling me would not throw a red flag. I have had LS1 and LS6 cars do that to me with no boost on the dyno. Changed the wheels and tires and it went away. Go figure.
Your 4.8l knock sensors is much more sensitive than a GN. There should be 2 knock sensors and these go into water jackets rather than block. One reason is that the coolant will actually transfer sound much better than cast iron or aluminum.
Massive changes in temperature can drastically change the way an ECM is controlling timing and fuel curves especailly since the tunning was done in the summer. The ECM bases a lot of its cold start run fuel and timing parameters off of the engine temp sensor not so much the MAT. IE the same fule and timing maps are being used even though there is colder denser air in the combustion chamber.
Another item is the formulation of fuel. Colder weather is usually associated with differnt formultations of fuel for cold weather. These can be additives to prevent freezing, and other components.
My recommendation would be to either get it retuned for cold weather and winter formulated fuel or just be careful mindful and a little easier on it.
The amount of knock you are telling me would not throw a red flag. I have had LS1 and LS6 cars do that to me with no boost on the dyno. Changed the wheels and tires and it went away. Go figure.
meanchicken
gallo vicioso
- Joined
- Oct 6, 2007
I'm curious...how could KR with no boost be real knock?
STS are the turbo kits that have the turbo and air intake fit in at the back of the vehicle and sit in place of the muffler, correct? Long legths of boost pressurized pipe running under the vehicle from back to front?
Are you sure you don't have a boost leak or rattle somewhere under there that might be contributing to flase knock when you are not placing the vehicle under load?
STS are the turbo kits that have the turbo and air intake fit in at the back of the vehicle and sit in place of the muffler, correct? Long legths of boost pressurized pipe running under the vehicle from back to front?
Are you sure you don't have a boost leak or rattle somewhere under there that might be contributing to flase knock when you are not placing the vehicle under load?
bmackinnon
Active Member
- Joined
- Feb 24, 2005
Not that it matters, but, for one, I'll throw the BS flag on the 'coolant transfering sound better than metal'.... any engineering vibes 101 book will tell you otherwise... there may be a reason for that placement of the knock sensor, but that's certainly not it.....
Secondly, I'm not sure what cold start fueling has to do with this anyway...
Third, the ecm has PLENTY of compensation room engineered in for ambient weather/temp changes via, among others, BLM/INT modifiers based on feedback from the O2 sensor... tuning for the weather should not be necessary for a closed loop feedback system... especially in this case, since the knock is occurring at intermediate throttle positions, where the system 'should' be in closed loop.....
I WILL, however, perhaps buy the winter fuel formulation theory.... I would try running some good fuel in it and see if that has a measurable effect...
My humble O2...
Thanks guys for all the info. I have scheduled a retune for next Saturday when I am off of work. For now I am just going to take it easy and run some race gas in the motor to see if no knock will occur. Man, I love having a gas station right up the street that sell 100-110 octane at the pump
