KR When MAF is Operable
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Teching In
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KR When MAF is Operable Has anyone found this to be a problem? First a little background.
Running an '05 LS2/T-56 with an '03 Vette computer. The VE table is trimmed out to within a few 1s and 0s LTFT. Using a stock '03 Vette pedal, tac module(must be used because the throttle by wire LS2 throttle body is being used), pcm, knock sensors (located in the sides of the LS2 block) and MAF. With the MAF in fail the knock is just not there. With the MAF operable the knock is mainly with 75%-WOT. Getting atleast 10 degrees of KR. No audible knock present. Suggestions of what to log and look at and what might be causing the problem...
Running an '05 LS2/T-56 with an '03 Vette computer. The VE table is trimmed out to within a few 1s and 0s LTFT. Using a stock '03 Vette pedal, tac module(must be used because the throttle by wire LS2 throttle body is being used), pcm, knock sensors (located in the sides of the LS2 block) and MAF. With the MAF in fail the knock is just not there. With the MAF operable the knock is mainly with 75%-WOT. Getting atleast 10 degrees of KR. No audible knock present. Suggestions of what to log and look at and what might be causing the problem...
TECH Apprentice
Joined: Oct 2004
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From: Katy, TX
Is your MAF calibrated? You might also try bumping up the ETC maximum predicted airflow. It's possible that you're exceeding seeing as you have more cubes than an LS1 and better airflow characteristics. Does it throw any codes?
I agree, the MAF being out of calibration is one of the main culprits of seeing knock if the VE tune is correct. If you have a wideband, you will need to calibrate it that way, for best results. Otherwise you will have to use the fuel trims to help richen up the MAF signal when knock is detected. What are you using to tune with?
Thread Starter
Teching In
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I am using a LC-1. Tuning and data logging with HPT. I just took the car for a spin and the car runs great with the MAF in fail mode. Turn the MAF on and the car gets 10 degrees of knock retard with your foot into it. With the MAF turned on the car is too rich if anything. We are talking 10.5-11 at WOT at 3600-4400RPM. There is no audible knock present. I have not calibrated the MAF yet since I have not decided on which method of attack is best. Lots of good info here on the forum. There is a knock code. I will have to scan it and let you know the exact number. ???????
Thread Starter
Teching In
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I have not adjusted the timing. The stock timing table for the '03 LS6 works just fine with no knock untill I allow the MAF into the equation. I have an extra brand new MAF I am going to try. I am also thinking about trying new knock sensors or the LS2 knock sensors. Any suggestions are appreciated.
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Thread Starter
Teching In
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No LTFT going nuts, but they do show alot of positive numbers such at 5's up to 9's in the 15 to 35 kpa (idle->4400rpm) with the MAF enabled. With the MAF disabled, all LTFT's are 0 to -3. Timing and MAF are related to each other? Only getting knock with my foot in it.
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Verdad Gallardo TECH Apprentice
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From: Katy, TX
What is your AFR at WOT in SD? It definitely sounds to me like your MAF calibration is out of whack. Is there any particular reason you want to keep the MAF? Why not just run SD? I've been doing it for a year and love it. 
Thread Starter
Teching In
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Average WOT in SD is 11.9AFR. I would like to solve the problem instead of working around it by eliminating the MAF. Why could I get false knock from using the MAF when by using the MAF the engine is running too rich not too lean? We are talking about 10.5 AFR at WOT when the MAF is enabled. Too much fuel=false knock? Is the PCM retarding the timing because 10.5AFR is too rich for WOT?
TECH Enthusiast
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From: Birmingham, AL
Can you tell us what the timing looks like when you're getting knock, and at what kPa? When the MAF is disabled, I believe the PCM reverts to the low timing table. Did you copy high to low before disabling the MAF?
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Teching In
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I did copy over the High Octane to the Low Octane table.
RPM KPA Knock Retard Advance AFR
3600 90 5 18 12.8
3600 95 10 12 10.5
3600 100 10 11 11.8
4000 90 10 11 10.8
4000 95 10 10 10.5
4000 100 10 10 10.7
4400 90 10 10 11.1
4400 95 10 10 11.1
4000 100 10 10 10.9
These are a few
RPM KPA Knock Retard Advance AFR
3600 90 5 18 12.8
3600 95 10 12 10.5
3600 100 10 11 11.8
4000 90 10 11 10.8
4000 95 10 10 10.5
4000 100 10 10 10.7
4400 90 10 10 11.1
4400 95 10 10 11.1
4000 100 10 10 10.9
These are a few
Last edited by SouthStreet; Jul 7, 2006 at 03:02 PM.
TECH Enthusiast
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From: Birmingham, AL
Your tmiing at WOT looks good (assuming you can get rid of that knock). Here's something I did to see if my MAF was off... First, I set the MAF Fail freq to 1. I logged MAF (lb/min) and Dynamic Air, and just drove around to hit various cells in Histo #3. I exported the log, and looked at the maf lb/min and dyn air side-by-side. If the MAF reading is lower than the dyn air, the MAF isn't reporting enough air, and if it's higher, it's reporting too much air. I scaled the entire MAF table by 1% until my fuel trims with the MAF enabled got to a liveable #. This worked for me but doesn't mean it'll work for you. It also doesn't mean its correct lol. Just throwing something out there for ya. You definitely wanna get rid of those really positive fuel trims regardless. Or, you could skip all this, and multiply your whole MAF table by 110% and see if the knock goes away. Either way, good luck with it.
One more thing. Let's say you ease to 4400 rpms at about 25% throttle...do you get knock then also?
It also doesn't mean its correct lol. Just throwing something out there for ya. You definitely wanna get rid of those really positive fuel trims regardless. Or, you could skip all this, and multiply your whole MAF table by 110% and see if the knock goes away. Either way, good luck with it.One more thing. Let's say you ease to 4400 rpms at about 25% throttle...do you get knock then also?
Last edited by WS6 GreeN; Jul 7, 2006 at 05:05 PM.