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Thread: false knock at idle??

  1. #1
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    false knock at idle??

    I have a 95 f body with lq4 6.0 and I am getting knock at idle and on a warm start sometimes. this is my first go at a ls style engine/ tune Got tired of my lt1 problems so I built a 2003 lq4 6.0 with some unported 243 heads milled .030 to about 11.2:1. A brian tooley / comp cams grind 231/242 .617/.593 112 lsa with 12 degrees overlap ls6 intake and stock tb, longtubes, no cats and open headers right now I have the idle timing in gear and in park, also high and low spark all set the same. And pretty low actually compared to what i've seen and read but I did mill the crap out of the heads..... could the open headers cause false knock?? I do have about 18 inches of pipe on the headers to make the o2 sensors work I also have a hanging idle after opening the throttle, a flare on start up, and a hesitation off idle in gear and in park but right now I figured start with base timing and then I can move to the idle issues then at least I can drive it down the street and go from there with ve and maf tuning
    any suggestions on the timing would be greatly appreciated thanks
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    Last edited by jason k; 07-14-2015 at 11:40 PM.

  2. #2
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    I know aftermarket cams can create false knock not sure about open headers most likely you will have to desensitize your knock sensors a little how much I couldn't tell you. Id check at idle what the timing is advanced at you know if its like 10* at idle and your getting kr its false. how much is it showing and is it constant? I know with my 99 my knock sensors are overly sensitive when I look at my scans i can see the kr line underlining when ever i use throttle doesn't register as kr but its definitely listening hard. Another thing to keep in mind is look between the years of trucks (tune repository) seems like the later the year the more the sensor has been desensitized for the stock truck gm tunes. just knowing where you can set it hopefully someone else with similar mods can shed the light where they had success desensitizing the sensor to where it doesn't hear false kr but can still protect from the real

  3. #3
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    On that scan I was at 18 degrees. I'm not sure where I have the over under set on this tune Thanks for the help I'll look at some other knock sensors tomorrow but I hate to desensitize it if it is actually knock. I have logs where it spikes and then slowly fades out. I'll post the worst log tomorrow when I get to the shop

  4. #4
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    ok I finally got the exhaust on ( didn't install the widebands yet) I made a bunch of changes to the spark tables, did a VE tune and a MAF tune, and am working on figuring out the throttle cracker and rolling idle issues. It definitely runs much better no more knock at idle or on a restart. As I am coming to a stop I get about 6-8 degrees of knock retard. The rolling idle is out of control, as soon as I stop the idle comes down normal but it is on cruise control when moving. Im wondering if the rolling idle issue is causing a lean knock from the IAC hanging open?? I am also running VP C109 in case it was an octane issue Any thoughts on my spark tables ? Im concerned about knock because of the 11.2 :1 and being in New England we have the worst fuel around
    in progress pt 6 maf and ve tuned.hptfirst beating 6.0.hplmy default imperial ve tune.cfgVCM Scanner.cfg

  5. #5
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    also I converted a dbw to a dbc and copied a express tune onto my Silverado tune but now I see major differences in and express dbc to a Camaro dbc should I have used the Camaro info instead? some tables are different between the 2 files. The truck had the rolling idle disabled and also zeroed out for instance and assume that was because dbw did I cause the rolling idle issue by coping the wrong info? thanks in advance for and help

  6. #6
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    ok I have tried changing the timing a few dozen times I am down to 8 degrees at idle in most areas and when I come to a stop I am still getting a ton of knock. I have tried a couple of different race fuels, right now I have vp 110 leaded which is 107 motor octane, still about the same knock. I have tried adding fuel by the ve table a few times until it seemed to get worse from too much fuel, and then I backed the ve table back. I have notched the frame where the exhaust was hitting, and no difference. I have tried many different timing tables from the repository, some stock tunes from different cars and trucks that I have downloaded that have been in my shop, still nothing. I fixed my rolling high idle thinking that was causing a lean spike, no help there either. I also have done a ve tune and a maf calibration, which got the fueling pretty close according to the trims but still about the same as far as the knock retard. I looked at a few different knock sensor settings in the repository, and in my stuff, and mine are pretty close if not the same as all the other trucks. I hate to desensitize the sensors if it really is knock. If I back them down too much what about on the high rpm when they need to be sensitive??
    As I have said I shaved the heads a quite a bit and notched the pistons a lot so I am pretty concerned about spark knock. I feel like I perforated my pistons and with a decent amount of knock well BOOM might be possible I do have widebands one on each bank, they are not hooked into the scanner (haven't figure that out yet) so I am pretty confident that my fueling is close, actually a tad rich in PE again trying to rule out fuel as an issue
    here is my tune and scan with 12 degrees at idle and the log with knock when coming to a stop
    95 z28 with 6.0, 243's milled .030 to about 11:1, ls6 intake and tb, brian tooley stage 3 231/242 617/593 112 lsa , fast/ areomotive fuel system, 1 7/8 tsp longtubes, no cats, turbo 400, 36 lbs GTP injectors

  7. #7
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    could poly engine and trans mounts be the cause, transmitting too much vibration? what about stainless long tubes being just too noisy? I have removed all the adders from the timing tables to try to eliminate all those issues also
    95 z28 with 6.0, 243's milled .030 to about 11:1, ls6 intake and tb, brian tooley stage 3 231/242 617/593 112 lsa , fast/ areomotive fuel system, 1 7/8 tsp longtubes, no cats, turbo 400, 36 lbs GTP injectors