2012 LGT, stage 1, not hitting boost target with extreme cold weather ~10 degrees F.

Hi,

 

I have a 2012 legacy GT with OTS stage 1 tune from Cobb.

 

I usually hit ~17psi of boost regularly, however with the recent cold weather (6-15 degrees F), i have only been able to hit around 12-13psi.

 

Car runs fine. Is it just an effect of this unusually code weather??

 

Anyone else experienced this?

I wonder if your BPV is getting stuck slightly open. Is it still the stock plastic unit?

stock BPV. Is there a way to check?

Usually, in colder weather, you would tend to overboost not underboost. So, check if you have any vacuum/boost leak. How do your long term fuel trims look like?

I did notice some overboost, but that was when the outside temperature was around 30-40 degrees.

 

I can do some data logging. What am I looking for on the long term fuel trims?

 

Thanks for the help

Any chance the iat is keeping the ecm in low boost.

 

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I have noticed my car does the same thing on really cold days as well with the Cobb AP stage I OTS tune.

Check target boost and boost error that will tell you if the car is doing what the tune says.

 

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i will take a look at the target boost and boost error.

 

I am glad I am not the only one that is having this issue!

yeah do check these.

 

Regarding the fuel trims, if you have an AP, then you are looking for the A/F learn values. You want them to be within +/- 5%.

i will take a look at the target boost and boost error. I am glad I am not the only one that is having this issue!

Sounds good. Its not really an issue though just as FLlegacy and xt2005bonbon mentioned already!

 

Typically just a function of your ECU programming and tune.

Its expected that with relatively large differences in ambient air temp, your MAF/IAT sensor combo will see either: cold, humid aka more and denser air with more oxygen content per gram or hot and dry aka less and sparse thinner air with less oxygen content per gram.

 

Your MAP sensor in the intake manifold will in turn see different post-turbo air-charge characteristics in the same turbine and bpv operating zones.

 

This is where various things happen in the ECU routines... altitude, intake/manifold temp compensations, coolant temp compensations, MAP Load compensations, timing compensations, various stability tables, etc etc.

 

Hence typically your Commanded/Target Boost will be lower if the car sensors see cold winter and/or denser low altitude air, say -10C and <40% humidity, <500m elevation, your ECU may command a target boost of 14psi, you may hit 13psi and make x wtq/whp

 

If you automagically teleport the car to an area with 30C, 90% humidity and/or 1,000-2,000m elevation, your ECU may target up to 18-20psi, you might his 21psi and output the same x wtq/whp.

 

All in the tune (including stock), pre and post-turbo leaks, target boost -> boost error and the multitude of compensations the ECU applies.

/\pretty much exactly what he said above.

 

These cars have about 20% correction at 14 degrees and about 10% at 32. The 15+ WRX has TONS of temp comps as it gets colder and the 10-12 LGT was the original test bed for the low mounted turbo system used for the 15+.

 

I would say its pretty normal with your setup.

 

Dave

I'm also having this issue, but it's coming with other symptoms. I just finished a timing belt and thought maybe I left something loose, but I didn't have any issues for the 3 weeks I've been driving it. The other day i heard some kind of a thud while driving and now have a noticeable vibration/shudder noise whenever the car is under load. It happened right around the same time the cold hit and started affecting boost but I'm not sure if they are related or coincidence.

 

Target boost is still reading a peak of 16.96, which is weird. I'd be less concerned if the ecu never expected to get full boost, but if target boost is what it sounds like, I'd think the engine would run rich if it was getting less air than expected.

I can only reach 12-12.4 lbs of boost. Weather is 16 degrees

Cobb stage 1 93 oct

Issues under load occur only when clutch is engaged.

Disengage clutch and vibration and the noise stops

Noise is less noticeable when not on the throttle, but does not get worse when I get into boost (it gets gradually louder with more load, but reaches a max volume before i go from vacuum to boost)

 

I think I changed my mind. Rereading my post and the two issues seem unrelated and I probably have a drivetrain issues in combination with this tuning issue.

 

It's too damn cold

The weather got up to 34 degrees today and I was able to reach peak boost. However, it did seem like it capped me at 13 pounds after a half hour of driving. I thought ambient temperatures were affecting it but now I think it has to with intake air temps. I wasn't monitoring intake temp but I have a feeling it was higher when I started driving (car warmed up for a half hour) and as intercooler got colder the computer turned down boost. I have to say I'm not a fan of it. The car definitely loses some power.

Welcome to the 'wonderful' world of Subaru engine managment

and ECU logic routines.

 

If you 'feel' a loss of power something else is going on, not just your target and achieved boost levels fluctuating (as they should).

 

If you're really interested in knowing more of the 'why', get a proper logger such as BtSsm or RomRaider, worse case FreeSSM, or configure your AP if using COBB and log away!

Learn to interpret and make use of the data, see what the sensors and ECU are telling you, setup tests to learn more, rinse repeat.

 

Otherwise, just live with the symptoms of whatever is happening

or pay someone to hopefully 'fix' it for you with an e- or pro-tune.

 

Disclaimer: 'Ignorance is bliss' is especially true with all things recent/current-gen Subaru. If you end up down the 'why?' rabbit hole, you might soon enough catch yourself reading or wanting to post in threads like this:

 

http://legacygt.com/forums/showthread.php/target-boost-cant-get-you-267319.html?t=267319&highlight=btssm

Oh. So me no go fast in cold?

 

Thank you

You should be able to go just as fast in Christie/Cuomo'land summer at the shore or arctic blast mode... that is 55 or 65mph on the Turnpike or 25mph in town lol.

 

If your butt dyno feels a weaker disturbance in the EJ25 force, then problem with old car somewhere else is.

That's interesting all this change of boost level when it gets colder. I guess my tuner did not bother doing this cause mine will always hits 18.5-19.1 psi cold or hot outside.

 

Perscitus, do you know if this ECU logic applies to the stock 05-09 tunes?

I havent loked at those ROMs but my gut tells me, likely yes.

 

Our vendor tuners will know for sure.

 

Are you getting low boost errors with that same consistant target and achieved boost, regardless of whether its 90F or 15F outside?

If so, that is odd and would likely be a function of your non-OE tune.

Why and who would set things up like that though beats me.

Are you getting low boost errors with that same consistant target and achieved boost, regardless of whether its 90F or 15F outside?

 

Pretty much. The boost targets I have are essentially the same regardless of temps. And my 06 is able to reach the boost target values very consistently with minimal errors (like 0.1 psi or 0). Although I admit if it is very cold, then it may tend to overboost a bit in specific load range (like 0-1 psi). But keep in mind that I have a cobb air intake, which I think tend to favor boost creeping or something.

In hot weather, I usually meet the boost targets too with very good accuracy and almost never overboost.

 

Edit: I should specify that my comments pertain to comparing peak target boost vs. peak actual boost. I admit I have not really looked at an actual timeseries of boost errors while 'WOTTING'. <--

Got it, in which case have a look at cruise boost errors and half/two-thirds throttle boost errors. Might need a tuner familiar with pre 06 4th gens to chime in and have someone look over your config too.