Back to stock boost?

When I picked up the GT from the body shop I noticed the AP was unplugged from the OBD port. It didn't really surprise me since they plug their tool into it to check for codes. The weird thing is since I got it back, it has maxed out at around 12.75 psi boost. Before it would get into mid 15 psi (OTS 91 map). I have re flashed the ECU but no change. I have yet to check for boost leaks, but wanted to know if anyone else had a suggestion.

 

Also, I think I remember someone saying recently that with the summer heat you loose a pound or so boost, but it acts the same on cool mornings as well.

Check your boost error on the AP. If it's below 1 psi, the car's targeting a lower boost pressure. If it's larger, you probably have a leak or a boost control issue.

Is the body shop, a Subaru dealer? I hope they didn't refreshed the stock tune.

Is the body shop, a Subaru dealer? I hope they didn't refreshed the stock tune.

 

That was what I thought happened. It could be standard practice for a collision. So I re-flashed the Cobb tune and the max boost didn't change.

Check your boost error on the AP. If it's below 1 psi, the car's targeting a lower boost pressure. If it's larger, you probably have a leak or a boost control issue.

 

There is no error. It's just that boost is lower than normal, back to stock levels.

Boost error (or something like that) is a parameter that you can log.

^^ what he said. You have the ability to either log the boost target and actual boost, or the difference between them (boost error) on the AP. This will tell you whether you're underboosting, or whether you're really just targeting a lower boost level.

Ah, didn't know that. I'll swap one of my gauges to that after work to check it out.

I'm guessing the gauge I need is "TD Boost Error"?

Yep. Positive boost error means you're underboosting the target the ECU is setting, negative boost error means you're overboosting the target.

So, something seems to be up. I logged my drive home and this is the log:

 

https://drive.google.com/file/d/1LGaCCuCvfT_oB5Lv3Bq4lRKMNYjasvNa/view?usp=sharing

 

It is underboosting, but I am letting the engine cool down before looking around.

Looking at your log it looks possible that you do have some underboost at WOT. I'd also figure out why your DAM is less than one. Does the 5th gen LGT start with a DAM of 0.5 after a reflash/battery disconnect like the 5th gen?

 

Just took a look at long term fuel trims and short term corrections during the idle stretches and they don't seem to support a vacuum leak, though.

Edited July 14, 2020 by awfulwaffle

Ok, so where do I go from here? What would cause underboost if it's not a leak? Three things come to mind: the turbo, boost control solenoid, or the bypass valve.

I'd still check for a boost leak to be sure, though it seems unlikely. After that, I'd check if the wastegate actuates by hand, try swapping out a known good boost control solenoid, and pressure test the BPV. If all that checks out, I'd drop the downpipe and take a look at the turbo for shaft play/wear, and wastegate flapper misalignment.

 

DAM question still stands, maybe someone from 5th gen land can chime in.

 

Another question - what did the shop do on your car? I assume you're positive you were hitting target boost before they worked on it?

They repaired the rear bumper. I can’t be 100% sure it was boosting normally before. On my normal commute I hit 13-14 max on an on ramp. Never noticed till I got it back that it was lower.

 

Before and after:

 

 

 

 

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DAM definitely starts at 1.0 after a reflash. That is definitely something i'd look into as well.

 

I don't think they're related, but definitely check for a boost leak first and foremost. If you have the stock intercooler and charge pipe, the section where those two mate leaked the most for me.

 

For the DAM, check your plugs, clean your MAF and get some good gas to start.

What's the recommended way to check for a boost leak? I've seen some DYI's online to make one using a pressure regulator.

https://legacygt.com/forums/showthread.php/easy-5th-gen-gt-boost-leak-test-255163.html?t=255163&highlight=test+boost+leak

 

That link should help you test for boost leak.

 

Did you do a visual in the engine bay and under the car to make sure nothing is disconnected or out of place?

I use this with my pancake compressor https://www.amazon.com/dp/B0825WNGP3/ref=cm_sw_r_cp_apa_i_uZ4dFb7236SBV

I pulled the engine cover off last night and looked around. Nothing jumping out at me. Hopfully this weekend I'll have time to jack it up and remove the splash shield to check out the underside.

I use this with my pancake compressor https://www.amazon.com/dp/B0825WNGP3/ref=cm_sw_r_cp_apa_i_uZ4dFb7236SBV

 

Do you attach this to the turbo, or to the intake pipe where the MAF is?

Edited July 16, 2020 by Falcor

I cleaned the MAF tonight. It is crazy humid in the garage, so I’ll see how it does in the morning on the way to work.

 

 

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The drop in boost is still there, but it did feel smoother after cleaning the MAF.

Do you attach this to the turbo, or to the intake pipe where the MAF is?

 

I take off the intake box and put that in the intake pipe

Check your vacuum lines on the intake manifold and hardlines on passenger side that are near the charge pipe from turbo.

 

Verify the coupler on the tmic to tb didn’t start to blow out.

 

Double check your tmic endtanks for separation.

 

 

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