Help understanding Cobb logs

tom · 08-17-2011, 05:35 PM

I've recently installed my Cobb AP and want to make sure I'm understanding my logs correctly. I'm running a stock 335i on 91 octane gas in CA with the ACN91 Cobb maps. These first two logs are 3rd gear pulls in ~70*F ambient temps.

If I understand what's happening correctly, there is a throttle closure on both logs between 3000-3500rpm, which is a known issue with Cobb stage 1. I believe my AFR looks good as it slowly targets 12, which is what I read to be about expected. My timing seems low, especially in the first log, but doesn't appear to have any sharp drop outs. I don't know how to interpret the WGDC value - it is way lower than most logs I've seen posted with other tunes, but it seems about normal compared to other Cobb logs. I think it's weird how it climbs up as opposed to staying flat, is that normal? My IAT's as logged in the 2nd log climb quite high but I am getting an FMIC installed soon which should fix that issue. Is there anything else I'm missing or wrong thinking?

Secondly, I've been having a low rpm low load jerking during cold starts in the morning. This has happened both tuned and untuned, but now that I have Cobb I decided to make a log out of it.

It appears that there is a throttle closure and widely varying AFR. If I were to naively guess, I'd suggest there might be an issue with my injectors that's spiking the AFR to be so lean. Could anyone offer an opinion on this log?

Thanks!
Tom

Jeff@TopGearSolutions · 08-17-2011, 05:45 PM

Some throttle closure is normal so as long as your not feeling it. This is how the Cobb and the stock DME control overboosting conditions.

Your timing looks good and your AFR appear to be normal as well.

As long as your intake air temps are not exceed 150 I would presumably say your OK.

The lower the WGDC the better.

All in all everything seems to be in check.

Litos · 08-17-2011, 05:54 PM

i'm no expert and i'm still learhing but the first thing i looked for was TPS and Boost.

i did see closure @ 15.6psi, much like my car did.

one thing i did notice, and maybe someone can explain, is that the first pull shows 15psi all the way across the board.

the second pull appears to show boost in the 13's all the way across the board.

shouldn't it have climbed to 15.5 and dropped to @ 12 or 13 by redline?

those 2 pulls are not very consistent to me......

themyst · 08-17-2011, 06:03 PM

Am I the only one who sees boost at 11-12 psi on those logs? Unless the ACN91 octane maps have a lower load target than the 93 octane maps?

tom · 08-17-2011, 06:08 PM

Both logs should show boost settling between 11-12 psi after the throttle closure is over. I think this is what ACN91 is targeting since I have not seen a higher sustained boost while driving and using the AP to show me boost real time. I'm also in rather cool low humidity weather, which may allow my car to boost lower to hit the load targets.

I was planning on moving up to the regular 91 octane map if everything looked good, should I try this and log again?

Litos · 08-17-2011, 06:09 PM

oops, i'm a tard - i was looking at the blue numbers on the right when looking at the pink lines......

....learning curve lol....

tom · 08-17-2011, 06:18 PM

Me too, don't worry about it.

Does anyone have any theories about the third log I posted with the throttle closure at low rpm / low load? There's a noticeable jerk when the car dips rpms and it is a tad disconcerting.

Litos · 08-17-2011, 06:38 PM

Quote:

Originally Posted by tom

Secondly, I've been having a low rpm low load jerking during cold starts in the morning. This has happened both tuned and untuned, but now that I have Cobb I decided to make a log out of it.

It appears that there is a throttle closure and widely varying AFR. If I were to naively guess, I'd suggest there might be an issue with my injectors that's spiking the AFR to be so lean. Could anyone offer an opinion on this log?

Thanks!
Tom

every monring your car will be groggy and drive like shit when it's cold.

happens to me all the time - by the time i get out on the highway my car is seeing @ 130 degrees.

after about 4 or 5 minutes of driving in the hot humidty, it reaches 180.

never wide open throttle your car if it has not reached @ 180 dgrees because it will jerk and shake like crazy.

i don't think it's tune related though

08-17-2011, 05:35 PM	#1
tom Enlisted Member 1 Rep 35 Posts Drives: Bmw 335i Join Date: Aug 2011 Location: Norcal iTrader: (1)	Help understanding Cobb logs I've recently installed my Cobb AP and want to make sure I'm understanding my logs correctly. I'm running a stock 335i on 91 octane gas in CA with the ACN91 Cobb maps. These first two logs are 3rd gear pulls in ~70*F ambient temps. If I understand what's happening correctly, there is a throttle closure on both logs between 3000-3500rpm, which is a known issue with Cobb stage 1. I believe my AFR looks good as it slowly targets 12, which is what I read to be about expected. My timing seems low, especially in the first log, but doesn't appear to have any sharp drop outs. I don't know how to interpret the WGDC value - it is way lower than most logs I've seen posted with other tunes, but it seems about normal compared to other Cobb logs. I think it's weird how it climbs up as opposed to staying flat, is that normal? My IAT's as logged in the 2nd log climb quite high but I am getting an FMIC installed soon which should fix that issue. Is there anything else I'm missing or wrong thinking? Secondly, I've been having a low rpm low load jerking during cold starts in the morning. This has happened both tuned and untuned, but now that I have Cobb I decided to make a log out of it. It appears that there is a throttle closure and widely varying AFR. If I were to naively guess, I'd suggest there might be an issue with my injectors that's spiking the AFR to be so lean. Could anyone offer an opinion on this log? Thanks! Tom
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08-17-2011, 05:45 PM	#2
Jeff@TopGearSolutions 3441 Rep 79,211 Posts Drives: C6 Z06, 09 335i, 10 335xi Join Date: Dec 2008 Location: www.TopGearSolutions.com iTrader: (37)	Some throttle closure is normal so as long as your not feeling it. This is how the Cobb and the stock DME control overboosting conditions. Your timing looks good and your AFR appear to be normal as well. As long as your intake air temps are not exceed 150 I would presumably say your OK. The lower the WGDC the better. All in all everything seems to be in check.
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08-17-2011, 05:54 PM	#3
Litos Banned 220 Rep 2,991 Posts Drives: 2012 Challenger RT Junk Join Date: Dec 2010 Location: Houston/Pearland iTrader: (1)	i'm no expert and i'm still learhing but the first thing i looked for was TPS and Boost. i did see closure @ 15.6psi, much like my car did. one thing i did notice, and maybe someone can explain, is that the first pull shows 15psi all the way across the board. the second pull appears to show boost in the 13's all the way across the board. shouldn't it have climbed to 15.5 and dropped to @ 12 or 13 by redline? those 2 pulls are not very consistent to me......
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08-17-2011, 06:03 PM	#4
themyst Major General 177 Rep 6,631 Posts Drives: '16 MK7 GTI Join Date: Feb 2009 Location: NYC iTrader: (8)	Am I the only one who sees boost at 11-12 psi on those logs? Unless the ACN91 octane maps have a lower load target than the 93 octane maps? __________________ E90 LCI N54 6AT
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08-17-2011, 06:08 PM	#5
tom Enlisted Member 1 Rep 35 Posts Drives: Bmw 335i Join Date: Aug 2011 Location: Norcal iTrader: (1)	Both logs should show boost settling between 11-12 psi after the throttle closure is over. I think this is what ACN91 is targeting since I have not seen a higher sustained boost while driving and using the AP to show me boost real time. I'm also in rather cool low humidity weather, which may allow my car to boost lower to hit the load targets. I was planning on moving up to the regular 91 octane map if everything looked good, should I try this and log again?
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08-17-2011, 06:09 PM	#6
Litos Banned 220 Rep 2,991 Posts Drives: 2012 Challenger RT Junk Join Date: Dec 2010 Location: Houston/Pearland iTrader: (1)	oops, i'm a tard - i was looking at the blue numbers on the right when looking at the pink lines...... ....learning curve lol....
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08-17-2011, 06:18 PM	#7
tom Enlisted Member 1 Rep 35 Posts Drives: Bmw 335i Join Date: Aug 2011 Location: Norcal iTrader: (1)	Me too, don't worry about it. Does anyone have any theories about the third log I posted with the throttle closure at low rpm / low load? There's a noticeable jerk when the car dips rpms and it is a tad disconcerting.
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