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Old 01-16-2016, 11:53 AM   #1
simpleJ
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Default Cobb BIG SF intake fuel trim issues

Alright folks let's see if you are all having the same experience:

Installed the Cobb big SF and associated 93 octane map per the instructions exactly and have been having nothing but issues with the tune, which I believe is due to the scaling or turbulence in the intake.

-the filter was on the reccomended one inch, I then adjusted it to about 7/8 s of an inch which improved AF learning values to an acceptable range but not AFRs

-I put dielectric grease on the MAF cables

-I installed the coupler but fear it may be "backwards" although Cobb told me if it fit, it's on there correctly as it is not kinked or anything.

And onto the issue:

I was seeing wild AF learn values indicative of a leak, poor MAF scaling, or turbulence. This was ranging from +- 10 and spiking to about 15 in traffic. I adjusted the filter and saw a major improvement, values dropped to about +-6. However data logs on both show the car running lean as soon as soon as it hits open loop and pulls data from only the MAF.

AFRs spike at the open loop switch to about 12.3 then taper down to 11.3-12 when the car is targeting 11-11.6. In closed loop fueling is acceptable.

I played with the scales to no avail.

If I had a leak, in theory this should show more at idle where a 1 g/s leak should cause the ecu to add a significant amount more fuel than further up the rev range, instead the car is taking fueling out at idle, as much as -6% long term trim and a negative or near 0 short term trim. This tells me the metered air is less than the ecu is expecting, though my thought process could be erroneous here. If it was leaking it should be adding fuel to compensate at idle, one would think.

So, other owners and tuners, have you seen this issue?

Is it the coupler causing turbulence back to the MAF?

The Cobb map itself just not cleaned up enough?

A leak?

Or is the Cobb intake just a turbulent piece of junk?

Other mechanical issue?

Logs to follow


*Yes I know protune blah blah. I'm waiting for a GS TMIC. Also intake bro sounds, I'm aware. I know stock is suitable for power, but that's not as fun.
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Last edited by simpleJ; 01-16-2016 at 11:59 AM.
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Old 01-16-2016, 12:50 PM   #2
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When I bought the COBB catted/resonated J-Pipe I spoke to my tuner to see if an intake was worth buying before beginning the the tuning process. He said that it was but when I mentioned the COBB intake he cautioned to stay far away. He said the COBB intake was throwing MAF scaling all over the place and varied by upwards of 15% for every 2015/2016 WRX on his dyno. He highly recommended against it.

I then asked another tuner, who has provided sound advice to me in the past. He confirmed the same thing. Both recommended about 4 other intakes over the COBB one, for the same reasons you are mentioning in your post.

Sad to say, but it looks like COBB dropped the ball, this time around.


***Neither tuner sells intakes themselves, so they had no financial reason to sway me to one intake over another.
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Old 01-16-2016, 01:02 PM   #3
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Default Cobb BIG SF intake fuel trim issues

I just have a hard time thinking that Cobb of all vendors spent well over a year on an intake that has dead spots and turbulence. After install I am thinking there could be some variability in install methods, position of the intake within the box, filter, couplet that could lead to issues. Other intakes seem to eliminate that variability with better brackets and clearer instructions.

The angle of the Cobb piping makes it tough to get the filter on just right, and hard to center in the box.

My car isn't running dangerous trims right now but it is definitely leaner than desired
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Old 01-16-2016, 01:17 PM   #4
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I agree, it's not common for COBB to release a product that doesn't function properly. I ran the COBB intake on my '07 WRX and '11 STI with no complications. However, this is the first time I've ever had a tuner I trust advise me to stay away from a COBB product. And the fact that 2 of them urged me to stay away, really says something.

Like you said, it might just be that it needs to be installed perfectly and since it seems to be more difficult than the others (the AEM was an absolute breeze and dummy proof), it may just be that many aren't installing it exactly right.

I'm curious to see what other owners of the intake chime in to say about it...
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Old 01-17-2016, 09:25 PM   #5
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Added some logs, cruise, idle and 3rd gear to near redline. Very very very lean tonight.

To switch logs, use the drop down on the top left.


http://www.datazap.me/u/simplej/log-...data=6-8-11-21

Last edited by simpleJ; 01-17-2016 at 09:37 PM.
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Old 01-17-2016, 10:23 PM   #6
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I would take the intake off and have a professional tune done. Stock intake performs very well and is a lot safer. Wth the temp dropping its even more risky. Running lean is a bad thing.
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Old 01-18-2016, 02:31 AM   #7
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I installed the Cobb Big SF about 2 weeks ago now and I am having the same issues. AF learning and correction are all over the place now. Got the Cobb j-pipe and catback installed now too and it helped a little bit changing to the stage 2+ tune but still all over the place. It'll be interesting if Cobb has any insight. I sent them my logs the end of last week.
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Old 01-18-2016, 01:04 PM   #8
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I installed the Cobb intake about a month ago. I don't have any known issues, but I haven't really been looking for any, either. I'll keep an eye out now that you guys said something.

Would a protune help any?
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Old 01-18-2016, 01:25 PM   #9
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A protune may or may not help depending on the source of the issue. A leak or mechanical issue, no help. A tune or scale issue and it will be a help.

You should be taking an observing data logs, even if your AF learn is fine (which mine is now) you could have odd open loop fueling characteristic.

I'm still trouble shooting
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Old 01-18-2016, 01:41 PM   #10
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When an intake is erratic, virtually no protuner has the time nor inclination to "fix" it. It not only takes forever to do, in the end even the best efforts regardless of the time spent will completely solve the issues.

If an intake cannot be made to flow a consistently perfect MAF curve calibration... it is a constant threat waiting to bite you.

FURTHER:
It isn't the fuel trims themselves that are the scariest part, because those are generated at relatively lower loads. They just serve as signposts that point to where the real, engine threatening damages can occur... high boost and high loads. Up in those regions of the MAF curve the LTFT can lean out even the best AFR calibrations. But worse, unless the MAF curve is accurate in the higher MAF regions, those trims can combine with MAF inaccuracies. Guess what happens then.

Last edited by SeeeeeYa; 01-18-2016 at 01:55 PM.
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Old 01-18-2016, 01:51 PM   #11
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Default Cobb BIG SF intake fuel trim issues

^ this.

If I can't get it straightened out shortly it is coming off the car.

I basically know I am on borrowed time with these AFRs, and have been logging with caution, which is about the only time I mash the pedal hard enough to hit OL fueling. High temps or bad gas and it could be good night for my FA. Luckily I have not been knocking.

Turbulence is the enemy. In the mean time I'll be keeping the car in closed loop-where fueling is safe. It seems to me like the whole scale for this map just does not follow a steep enough curve. Too much fuel down low (idle) and too little up top. 1 tuner told me "that map needs work" and another said no issue just not as good as GS, but they are a big GS dealer... Hence why I would like the feedback.

Last edited by simpleJ; 01-18-2016 at 02:54 PM.
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Old 01-18-2016, 07:30 PM   #12
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Yikes!

Those AFR's alone would be enough for me to rip that intake off before I even turned the car on again.
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Old 01-18-2016, 08:26 PM   #13
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So today I looked at the intake again and ended up making a few small adjustments and it seems to look much much better and more consistent at both idle and under some power. Still afraid to mash the pedal and blow anything
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Old 01-18-2016, 09:07 PM   #14
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I just got mind in the mail today. It might be easier to throw it on ebay and just order the GS from less money!
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Old 01-18-2016, 10:50 PM   #15
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I've been sent a few datalogs to review this intake's MAF behavior.

I haven't had any time tuning it, but with the OTS map that Cobb released, it runs dangerously lean and weird.

Do not recommend.
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Old 01-18-2016, 10:50 PM   #16
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if you install it properly it seems like its not too bad. my problem was pushing the filter on a little too far and not having the filter centered in the box. readjusted it today and it looks good
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Old 01-18-2016, 10:51 PM   #17
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Quote:
Originally Posted by anjuna View Post
I've been sent a few datalogs to review this intake's MAF behavior.

I haven't had any time tuning it, but with the OTS map that Cobb released, it runs dangerously lean and weird.

Do not recommend.
can you post a log?
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Old 01-18-2016, 11:23 PM   #18
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Quote:
Originally Posted by Hunter_B View Post
can you post a log?
SJ can if he wants. He was one of the ones that sent me one.

I have to clean out my PM box, so I don't have any others.
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Old 01-19-2016, 12:11 AM   #19
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Quote:
Originally Posted by anjuna View Post
SJ can if he wants. He was one of the ones that sent me one.

I have to clean out my PM box, so I don't have any others.
okay cool. and excuse my ignorance but i really dont see anything wrong with the log that was posted at the top of this thread, but i am also fairly new to subarus. at full throttle it shows his afr dropping into the 11s which is actually rich and does not go lean until he lets off the throttle (as seen by the sudden drop in rpm), which would be expected. can someone enlighten me on the big problems seen by the log posted? thanks
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Old 01-19-2016, 01:18 AM   #20
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Quote:
Originally Posted by sc00ter View Post
Yikes!

Those AFR's alone would be enough for me to rip that intake off before I even turned the car on again.

Yup!

This is the leanest I have seen though, luckily it's not had to keep the car in closed loop, and that the car isn't knocking. Like I said, borrowed time here otherwise.

I also have another tune that is scaled about 10-15% rich as a test map that keeps things in the realm of normal. Only reason it is still on the car.

Think of all the poor souls who aren't logging this **** and have no idea?

Quote:
Originally Posted by Hunter_B View Post
okay cool. and excuse my ignorance but i really dont see anything wrong with the log that was posted at the top of this thread, but i am also fairly new to subarus. at full throttle it shows his afr dropping into the 11s which is actually rich and does not go lean until he lets off the throttle (as seen by the sudden drop in rpm), which would be expected. can someone enlighten me on the big problems seen by the log posted? thanks

If you look at my logs, I've also included the command fuel final (target fuel) and command map fuel (map target fuel) to show us what the car wants under that boost in current temps and conditions. I'm almost a point higher than that in this log shown. That's a bad thing, generally
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Old 01-19-2016, 01:29 AM   #21
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For those of you interested, here is the before filter adjustment.

http://www.datazap.me/u/simplej/log-...13-23&mark=204

Here is my "rich" scaled tune, wacky AF learns here but much better AFRs.

http://www.datazap.me/u/simplej/log-...ata=8-10-13-23

I switched back to this tune after the frightening logs above, which I ran for a logging exercise.
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Old 01-19-2016, 05:13 AM   #22
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I had similar issues with the Cobb intake and 93 OTS map. Needless to say, intake was taken off and sold and car is back to stock for now. I would advise anyone that is running this setup to use extreme caution. My car now has a miss/stumble at light throttle that has been there since I started using the intake and map. Guessing that I overheated one of the cylinders from being lean and cracked something.

SQ
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Old 01-19-2016, 10:00 AM   #23
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Quote:
Originally Posted by simpleJ View Post
For those of you interested, here is the before filter adjustment.

http://www.datazap.me/u/simplej/log-...13-23&mark=204

Here is my "rich" scaled tune, wacky AF learns here but much better AFRs.

http://www.datazap.me/u/simplej/log-...ata=8-10-13-23

I switched back to this tune after the frightening logs above, which I ran for a logging exercise.
You realise of course, that when you switched tunes... your trims were reset.

Did you then run your car normally long enough to have the new tune's trims stabilised? Otherwise your logs may be misleading.
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Old 01-19-2016, 10:12 AM   #24
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Quote:
Originally Posted by SeeeeeYa View Post
You realise of course, that when you switched tunes... your trims were reset.



Did you then run your car normally long enough to have the new tune's trims stabilised? Otherwise your logs may be misleading.

Yes sir- I am aware. There's a good bit of mixed driving, highway city, intentional open loop throttle sweeps and idle learning on each before taking a log. In the hundreds of miles for all but the "rich" tune. Which I will re-log once it has more than about 50 miles on it, which it did during the log I posted above.

This was not a case of log, pull over, reflash, log etc.
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Old 01-19-2016, 09:55 PM   #25
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Quote:
Originally Posted by SeeeeeYa View Post
You realise of course, that when you switched tunes... your trims were reset.

Did you then run your car normally long enough to have the new tune's trims stabilised? Otherwise your logs may be misleading.
A MAF cal is a MAF cal is a MAF cal is a MAF cal.

It should be accurate no matter the weather or if the tune is just being flashed.

When I had my 15, my trims were ALWAYS +/- 1-2% even if it had been a month down the road.

In my OPINION, trims are excuses.
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