FI question to pick your brains

GeorgiaTech335coupe · 08-06-2008, 02:56 PM

Guys,
My bro is getting a supercharger put on his 05 GT and is having a very weird occurrence. His car is showing knock (via datalog) when he gets off the throttle. This is happening even at very low rpms (2000ish) and at high rpms. Does anyone have an idea of what could be causing this? Thanks.

Sniz · 08-06-2008, 03:05 PM

Quote:

Originally Posted by GeorgiaTech335coupe

Guys,
My bro is getting a supercharger put on his 05 GT and is having a very weird occurrence. His car is showing knock (via datalog) when he gets off the throttle. This is happening even at very low rpms (2000ish) and at high rpms. Does anyone have an idea of what could be causing this? Thanks.

not me....PM DocGTO

scalbert · 08-06-2008, 03:14 PM

How much knock? What is the A/F ratio?

I wonder if it is missing due to going overly rich and being picked up as knock.

bdkevoIX · 08-06-2008, 03:35 PM

+1 AFR would help

GeorgiaTech335coupe · 08-06-2008, 11:43 PM

Im not sure what the AFR was, but it would happen after low throttle, low rpm, full throttle, high rpm. The guy that installed the SC went to great lengths to figure it out. Took everything off, inspected every single inch of the kit, flow tested the injectors, checked the pump, checked each cylinder on the dyno, switch the exhaust to a catless to see if it was backpressure. This stumped about every guy at Ford Racing that had a shot at it. Stumped a guy at Roush. The car showed knock even when on 100 octane.

scalbert · 08-07-2008, 08:26 AM

Have you tried replacing the knock sensor(s)? The knock sensor could be off a bit or even the A/D for that circuit in the ECU. It is not unheard of for this type of accoustic sensor to be bad and give false positives.

I assume there is no audible knock? When this occurs, what is the iginition timing?

stevenc · 08-07-2008, 09:06 AM

Could be false knock created by the noise and vibration of the blower. It happens.

unagi1 · 08-07-2008, 09:32 AM

The OP didn't mention anything regarding ignition. Did the guys verify the base / advanced timing, check plugs / gapping, replace wires, etc?

As mentioned could also be a false positive, did they actually "hear" any pinging / knocking while it was on the dyno?

scalbert · 08-07-2008, 09:33 AM

Quote:

Originally Posted by unagi1

Nobody's mentioned anything regarding ignition. Did the guys verify the base / advanced timing, check plugs / gapping, replace wires, etc?

Quote:

Originally Posted by scalbert

When this occurs, what is the iginition timing?

unagi1 · 08-07-2008, 09:35 AM

ok, ok...I fixed it

ezatnova · 08-07-2008, 09:36 AM

Likely false knock from things banging and shaking around.
Test the sensors (smack em with a wrench) to make sure they work, then try to isolate the problem (bad motor mounts, a heat sheild hitting, etc etc).

GeorgiaTech335coupe · 08-07-2008, 08:24 PM

The knock was audible from inside the car so it is there. They checked every single piece of the kit which included new plugs (Whipple kit). He even had a 91 octane tune from Ford Racing sent (we have 93 octane here), put 100 ocatane in and it still knocked.

scalbert · 08-07-2008, 08:32 PM

How long does the knock last? And you did say that even at light load and then lifting this occurs? This also did not occur prior to the blower?

Has anyone just pulled the belt off the blower (if possible) to see if it still occurs? What blower kit; does it have a bypass valve?

BTW, where is the car at?

08-06-2008, 02:56 PM	#1
GeorgiaTech335coupe Lieutenant Colonel 81 Rep 1,883 Posts Drives: Black BMW 335i coupe Join Date: Mar 2007 Location: USA iTrader: (0)	FI question to pick your brains - non BMW related Guys, My bro is getting a supercharger put on his 05 GT and is having a very weird occurrence. His car is showing knock (via datalog) when he gets off the throttle. This is happening even at very low rpms (2000ish) and at high rpms. Does anyone have an idea of what could be causing this? Thanks. __________________ Legal Disclaimer: Anything I or anyone else says about my vehicle on this website(e90post.com or any affiliated or nonaffiliated sites), pertaining to modifications, is only to gain acceptance from my/our peers, and does not actually represent anything actually existing on my car, and thus, cannot be held against me in any issues, i.e. warranty claims, that may arise.
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08-06-2008, 03:14 PM	#3
scalbert Major General 158 Rep 5,776 Posts Drives: '13 S4, '15 Q7 Join Date: Feb 2007 Location: Woodstock, GA iTrader: (8)	How much knock? What is the A/F ratio? I wonder if it is missing due to going overly rich and being picked up as knock.
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08-06-2008, 03:35 PM	#4
bdkevoIX Captain 18 Rep 739 Posts Drives: 06 Evo IX Mr Join Date: Mar 2008 Location: Maryland iTrader: (0)	+1 AFR would help __________________ 03 Golf TDI w/ r32 conversion - 120bph/40mpg ftw for now.. 06 Evo IX MR - 500whp,,,sold.....
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08-06-2008, 11:43 PM	#5
GeorgiaTech335coupe Lieutenant Colonel 81 Rep 1,883 Posts Drives: Black BMW 335i coupe Join Date: Mar 2007 Location: USA iTrader: (0)	Im not sure what the AFR was, but it would happen after low throttle, low rpm, full throttle, high rpm. The guy that installed the SC went to great lengths to figure it out. Took everything off, inspected every single inch of the kit, flow tested the injectors, checked the pump, checked each cylinder on the dyno, switch the exhaust to a catless to see if it was backpressure. This stumped about every guy at Ford Racing that had a shot at it. Stumped a guy at Roush. The car showed knock even when on 100 octane. __________________ Legal Disclaimer: Anything I or anyone else says about my vehicle on this website(e90post.com or any affiliated or nonaffiliated sites), pertaining to modifications, is only to gain acceptance from my/our peers, and does not actually represent anything actually existing on my car, and thus, cannot be held against me in any issues, i.e. warranty claims, that may arise.
	Appreciate 0 Quote

08-07-2008, 08:26 AM	#6
scalbert Major General 158 Rep 5,776 Posts Drives: '13 S4, '15 Q7 Join Date: Feb 2007 Location: Woodstock, GA iTrader: (8)	Have you tried replacing the knock sensor(s)? The knock sensor could be off a bit or even the A/D for that circuit in the ECU. It is not unheard of for this type of accoustic sensor to be bad and give false positives. I assume there is no audible knock? When this occurs, what is the iginition timing?
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08-07-2008, 09:06 AM	#7
stevenc Coming Soon 256 Rep 960 Posts Drives: 2015 BMW M4 Alphine White MT Join Date: Apr 2008 Location: Houston, TX iTrader: (0)	Could be false knock created by the noise and vibration of the blower. It happens.
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08-07-2008, 09:32 AM	#8
unagi1 First Lieutenant 15 Rep 397 Posts Drives: 2018 WRX, 2014 C63 507, 91 Mr2 Join Date: Feb 2008 Location: Elmsford, NY iTrader: (1)	The OP didn't mention anything regarding ignition. Did the guys verify the base / advanced timing, check plugs / gapping, replace wires, etc? As mentioned could also be a false positive, did they actually "hear" any pinging / knocking while it was on the dyno? __________________ 2018 WRX 2014 C63 507 1991 Mr2 Turbo
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08-07-2008, 09:35 AM	#10
unagi1 First Lieutenant 15 Rep 397 Posts Drives: 2018 WRX, 2014 C63 507, 91 Mr2 Join Date: Feb 2008 Location: Elmsford, NY iTrader: (1)	ok, ok...I fixed it __________________ 2018 WRX 2014 C63 507 1991 Mr2 Turbo
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08-07-2008, 09:36 AM	#11
ezatnova Power and Speed 105 Rep 2,197 Posts Drives: ‘22 Shelby GT500, ‘25 X5 50e, '21 Tacoma TRD OR Join Date: Jan 2006 Location: West Chester, PA iTrader: (5)	Likely false knock from things banging and shaking around. Test the sensors (smack em with a wrench) to make sure they work, then try to isolate the problem (bad motor mounts, a heat sheild hitting, etc etc).
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08-07-2008, 08:24 PM	#12
GeorgiaTech335coupe Lieutenant Colonel 81 Rep 1,883 Posts Drives: Black BMW 335i coupe Join Date: Mar 2007 Location: USA iTrader: (0)	The knock was audible from inside the car so it is there. They checked every single piece of the kit which included new plugs (Whipple kit). He even had a 91 octane tune from Ford Racing sent (we have 93 octane here), put 100 ocatane in and it still knocked. __________________ Legal Disclaimer: Anything I or anyone else says about my vehicle on this website(e90post.com or any affiliated or nonaffiliated sites), pertaining to modifications, is only to gain acceptance from my/our peers, and does not actually represent anything actually existing on my car, and thus, cannot be held against me in any issues, i.e. warranty claims, that may arise.
	Appreciate 0 Quote

08-07-2008, 08:32 PM	#13
scalbert Major General 158 Rep 5,776 Posts Drives: '13 S4, '15 Q7 Join Date: Feb 2007 Location: Woodstock, GA iTrader: (8)	How long does the knock last? And you did say that even at light load and then lifting this occurs? This also did not occur prior to the blower? Has anyone just pulled the belt off the blower (if possible) to see if it still occurs? What blower kit; does it have a bypass valve? BTW, where is the car at?
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