Is this false knock ??
08-11-2008, 04:16 PM
#1
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Is this false knock ??
My logs are showing a short bursts of knock (KC bumps about 200-300) and 5* spark retard between 3700 and 4200 RPM under higher acceleration (MAP 85-95 range. It showed up at 37* advance and cleared after PCM pulled retard. So I lowered the timing tables 5*, It then showed up at 32* and cleared at 5* retard. I then lowered timing another 5* and the darn thing still shows and pulls 5* down to 26 and then clears. I'm thinking this is false vibration. I had this prior to my cam and RR's install so I never went for the LT4 KM thinking I would be able to tune this out. I just ordered the KM, but wanted to see if anyone had some ideas on this ? Should I try going lower than 27* on my tables at the high end, that seems pretty low for 160 t-stat and 93 oct fuel.
08-15-2008, 09:43 PM
#2
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My logs are showing a short bursts of knock (KC bumps about 200-300) and 5* spark retard between 3700 and 4200 RPM under higher acceleration (MAP 85-95 range. It showed up at 37* advance and cleared after PCM pulled retard. So I lowered the timing tables 5*, It then showed up at 32* and cleared at 5* retard. I then lowered timing another 5* and the darn thing still shows and pulls 5* down to 26 and then clears. I'm thinking this is false vibration. I had this prior to my cam and RR's install so I never went for the LT4 KM thinking I would be able to tune this out. I just ordered the KM, but wanted to see if anyone had some ideas on this ? Should I try going lower than 27* on my tables at the high end, that seems pretty low for 160 t-stat and 93 oct fuel.
I am not sure what I am doing is right and any help would be appreciated.
08-16-2008, 09:59 AM
#3
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I am going to try a few more things. 1st- I have a LT4 KM on order. 2nd- Going to buy a fuel pressure gauge to make sure it's not starving at high load. 3rd- since it only shows up in Power Enrichment (PE) I'm going to disable PE temporarily to allow BLM updating at the high end and do a couple of sprints (0-60) in fuel cell 15 and see if it gets worse w/o PE adding fuel. For now I've left my knock retard alone to protect me in case it's a real condition. Once I 100% sure it's false I'll start working on the retard tables. My next mod will be LT headers and then a dyno/AFR tune, but I'll never get a good tune till get this this darn retard fixed. I'll update this post with results.
Last edited by bobdec; 08-16-2008 at 10:03 AM.
08-16-2008, 03:51 PM
#4
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With the mods you have I don't see where the knock is comeing from unless it is false.
I am going to put my old lt1 KM back in and see if that does anything. Some guy's have said thet they have had problems with the lt4 KM. Or it could be a bad lt4 KM. I'll try to keep you posted on how I make out. Good luck with your findings.
I am going to put my old lt1 KM back in and see if that does anything. Some guy's have said thet they have had problems with the lt4 KM. Or it could be a bad lt4 KM. I'll try to keep you posted on how I make out. Good luck with your findings.
08-20-2008, 03:33 PM
#5
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Ray, UPDATE.. installed the LT4 KM today and the knock at acceleration went away. I ran four 0-60 sprints at 100% TPS and no more knock at 37-4200. HOWEVER the LT4 KM is now showing knock during heavy deceleration with TPS=0%. Plan to tweak my DFCO to kick in at a higher MAP to see if cutting fuel off helps quite things down, my exhaust pops fairly loud during heavy decel but the LT1 KM never picked it up. Pain in the a*s fix one problem and another pops up.
Last edited by bobdec; 08-20-2008 at 03:38 PM.
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