Showing Knock in same area even with E85: Pre-ignition, Noise, Plugs?
09-30-2012, 04:23 PM
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Showing Knock in same area even with E85: Pre-ignition, Noise, Plugs? I've got persistant knock in two areas: right at launch and at the top of 2nd gear.
I can sometimes hear metal on metal when I don't launch full out (less exhaust and tire noise...), so I'm sure that is false knock. Plus I've turned up burst knock to the moon and it didn't help. A little more torque when launching won't help given my FWD layout, but I'm thinking about desensitizing it anyway so I can make legit 87 octane tables. How do I prevent the knock algorithm from reacting at just very low RPMs?
The knock at the top of second is more troublesome. I can run several degrees more advance through 1st than through 2nd (I don't top out 3rd with my gearing), in the ballpark of 6 degrees. The knock does go down if I pull timing, but it never seems to go completely away. I still get sporadic .5 degree readings even at 14* advance. If I just jump on the throttle on the highway, it won't knock until 6400rpm or so, but if I pull through second from first it can start as low as 5500rpm or so. I'm shifting at 6830, by the way.
To try and see if it was my compression causing the problem, I threw a tank of E85 in the car, adjusted stoich, and set PE to 0.85. It knocks exactly the same, or maybe a bit more. I read up on E85, and it looks like E85 has roughly the same MON as 93 even though RON is through the roof, so compression and detonation likely isn't my issue. I'd be tempted to think it's header or valvetrain noise because I can't hear the knock, but I think the computer is pulling timing before it gets that bad. So now I'm thinking that I have hot spots in my engine potentially causing pre-ignition, and that's slightly reinforced by the back four cylinders (cylinder 7 especially) showing most of the high rpm knock.
Does anyone have any insight to what might be my issue? I'm running a projected plug with heat range 6 (NGK TR6), so I was thinking going to a non-projected plug in heat range 7 (NGK BR7EF) or just going colder in general might help too. I'm thinking my 5.3 should like around 22-24* advance up top, and in general should like at least the same advance up top as it does at peak torque.
I can sometimes hear metal on metal when I don't launch full out (less exhaust and tire noise...), so I'm sure that is false knock. Plus I've turned up burst knock to the moon and it didn't help. A little more torque when launching won't help given my FWD layout, but I'm thinking about desensitizing it anyway so I can make legit 87 octane tables. How do I prevent the knock algorithm from reacting at just very low RPMs?
The knock at the top of second is more troublesome. I can run several degrees more advance through 1st than through 2nd (I don't top out 3rd with my gearing), in the ballpark of 6 degrees. The knock does go down if I pull timing, but it never seems to go completely away. I still get sporadic .5 degree readings even at 14* advance. If I just jump on the throttle on the highway, it won't knock until 6400rpm or so, but if I pull through second from first it can start as low as 5500rpm or so. I'm shifting at 6830, by the way.
To try and see if it was my compression causing the problem, I threw a tank of E85 in the car, adjusted stoich, and set PE to 0.85. It knocks exactly the same, or maybe a bit more. I read up on E85, and it looks like E85 has roughly the same MON as 93 even though RON is through the roof, so compression and detonation likely isn't my issue. I'd be tempted to think it's header or valvetrain noise because I can't hear the knock, but I think the computer is pulling timing before it gets that bad. So now I'm thinking that I have hot spots in my engine potentially causing pre-ignition, and that's slightly reinforced by the back four cylinders (cylinder 7 especially) showing most of the high rpm knock.
Does anyone have any insight to what might be my issue? I'm running a projected plug with heat range 6 (NGK TR6), so I was thinking going to a non-projected plug in heat range 7 (NGK BR7EF) or just going colder in general might help too. I'm thinking my 5.3 should like around 22-24* advance up top, and in general should like at least the same advance up top as it does at peak torque.
10-03-2012, 08:02 PM
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Following up on the pre-ignition hunch, I dumped Seafoam in a vacuum line, had a smoke show and some good results. I was now showing consistant false knock up until about 23* when it started showing real knock. The spark plugs read like they were too hot, so in went some BR7EFs. Now it doesn't knock, other than the same thing I see whether I run 10* or 26*, until 27*.
So, I think I just need to desensitive the knock sensors until I don't see any knock at say 22*, then throw 28* at the engine and make sure that I see a knock response.
So, I think I just need to desensitive the knock sensors until I don't see any knock at say 22*, then throw 28* at the engine and make sure that I see a knock response.
10-05-2012, 11:41 AM
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well the exhaust notes on the v6 versions throw all kinds of knock reading. try wrapping the headers and crossover. see if that help plus itll help keep the engine bay cooler.
10-08-2012, 12:33 AM
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Whatever the line worker torqued them to. I haven't touched them.
A degree or less after the seafoam. I scraped most of the carbon off when I changed the heads, but I didn't want to scuff the pistons so there was still some on them the last time I looked.
The headers are ceramic coated, and I didn't think wrapping them was a good idea. The crossover pipe is untreated aluminized steel, and I did wrap that.
I did desensitize them just a little bit, and it went away for now. I turned up the knock attack so it still pulls enough timing when I put the timing too high. I'll keep checking for anything mechanical as I install the last few parts here in the next couple weeks.
A degree or less after the seafoam. I scraped most of the carbon off when I changed the heads, but I didn't want to scuff the pistons so there was still some on them the last time I looked.
I did desensitize them just a little bit, and it went away for now. I turned up the knock attack so it still pulls enough timing when I put the timing too high. I'll keep checking for anything mechanical as I install the last few parts here in the next couple weeks.
10-08-2012, 02:01 PM
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I had the same problems and wound up doing the standard desesitizing of the sensors, didnt help
Switched to a non projected -8 and havent had any problems ever since. Though I can only run around 23-24* on my setup no matter what due to other factors
Switched to a non projected -8 and havent had any problems ever since. Though I can only run around 23-24* on my setup no matter what due to other factors
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10-08-2012, 03:38 PM
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What is your setup? I'm having some kr issues as well. I'm down around 23 at wot and still getting 1 or so kr. I'm gonna try some 104 to see if its compression related or false
