Low boost after shifting

[P M]

Problem: 1g 90 talon isn't boosting as 'responsive' as it should after gear shifting 'quickly'

Recently Added Mods: Evo III 16g and FMIC
Mods: FPR, Upgraded FP, Custom 3" DP & Exhaust setup w/ hi-flo cat, DSMLink, MBC hooked correctly tapped at J-pipe

Details: Recently added a FMIC kit with a brand new evo iii 16g. Fixed all boost leaks (boost leak test holds fine), oil leaks, and coolant leaks. My boost vac sits around -23 to -24 inHg. Full boost kicks in at 2800 rpm with boost set to stock 10 psi until i get injectors (car pulls very strong after adding in evo iii o2 housing and evo iii 16 g turbo).

My issue lies with shifting. If I start in 1st gear, i reach full boost at around 3000 rpm; after shifting to 2nd gear (landing around 3000 rpm), my boost drops from 10 psi to about 5 or 6 psi and it is struggling to get back to 10 psi, which it does reach when at 5500 rpm. The boost is less 'responsive' after shifting.

If I shift 'slowly,' meaning reaching full boost in nth gear (@ 3000 rpm), then letting off gas for boost vac to hit @ -23 inHG then WOT again, I reach full boost @ 3000 rpm in any nth gear, but only if I let off gas and hit -23 inHg.

Problem only occurs after shifting 'quickly' (1st to 2nd or 2nd to 3rd or etc.) I'm not venting to atmosphere, though the only immediate issue I see is the BOV return hose (from BOV to intake near intake filter) is slightly kinked so that it isn't shaped like an 'O' but more like an ellipse.

I'll see if I can take pictures and post them up. Any idea as to what is causing this would be great.


thanx
--P M

 

[Jst4Cyl]

I'd double check the bov.

Have you tried letting off the throttle when it is "non responsive" and then getting back on the throttle? (Giving the bov a chance to open and close)

Make sure that everything flows as it should. A kinked hose from the intake isn't going to help

 

[Bmxr152]

Check all lines and hoses, and do a boost leak test afterwards

 

[BoostFrenzy]

Do all of the above. And then since you have DSMLink, do a log where this happens and look very closely to what changes. It might just be something with the kinked BOV return.

EDIT:

But then again, I too have a Evo3 16G and my BOV is vented (Yeah yeah yeah...I know...BAD Nick, BAD!!) and my 2-3 and 3-4 shits I shift VERY fast and I am seeing no problems at all building boost again. So it may be something more. BTW, you say when you shift you drop back down to 3k. What RPM are you shifting at?

 

[Talesin]

Sounds like the CBV ('bov') is leaking. Please fill out your vehicle profile, along with the mod-list. Are you on the stock 1G CBV, or have you upgraded to some aftermarket type? Is it recirculated properly? You said that you're tapped into the j-pipe for your MBC, can you confirm that your BOV actuation vac line isn't teed off for anything, just a straight line from the manifold to the CBV?

Also could be a loose wastegate flapper or 'sticky' actuator.
Most ball-and-spring MBCs have a small plastic straight-through vacuum fitting that's supposed to go in-line between the MBC and the wastegate actuator, that has a pinhole drilled into the side, to avoid pressurelocking the wastegate open, which would also cause extremely slow/difficult spool.
Testing that's easy though... just take the MBC out of the loop. Run a straight vac line from the j-pipe to the wastegate actuator, and leave your MBC disconnected. Since there's no MBC in the way, it'll let air flow back out the way it came in, instead of having the MBC act like a check valve. If you get full spool after a 'fast' shift by 3Krpm, you might have to enlarge the pressure relief hole on that fitting just a bit.

 

[bighroder]

i would switch out your BOV for a new one.

 

[romeen]

the only immediate issue I see is the return big-hosed vacuum line from BOV to intake (near intake filter) is slightly kinked so that it isn't shaped like an 'O' but more like an ellipse.

Are you saying that the vacuum line to your BOV is connected to the intake pipe (pre-turbo) as opposed to the intake manifold? Unless I am misunderstanding you that would likely be your problem if that is indeed the case. If so, change it so that it is connected directly to the IM. Does it sound like you are getting compressor surge?

 

[P M]

EDIT:

BTW, you say when you shift you drop back down to 3k. What RPM are you shifting at?

I don't shift anything greater than 5700 rpm, it's not exactly 3000 rpm i land on, it's just a roundabout value I posted to show that i should be getting full boost almost right away after shifting, instead of getting this really weird lag

 

[P M]

Are you saying that the vacuum line to your BOV is connected to the intake pipe (pre-turbo) as opposed to the intake manifold?

i meant to say the BOV return hose (the big hose that comes off the 1g BOV into the fitting of the intake pipe between the filter and turbo); it is slightly crimped/kinked, where instead of it maintaining a consistent circular shape--it is oblong/oval shaped. I would imagine that it is still performing it's task as it should be though i'm not 100% sure I will re-check all my lines tomorrow.

 

[P M]

Sounds like the CBV ('bov') is leaking. Are you on the stock 1G CBV, or have you upgraded to some aftermarket type? Is it recirculated properly? You said that you're tapped into the j-pipe for your MBC, can you confirm that your BOV actuation vac line isn't teed off for anything, just a straight line from the manifold to the CBV?

My talon was never vented to atmosphere, though i noticed that the sound of my stock 1g bov was less loud after putting in the new turbo and FMIC compared to when i was running stock 14b and SMIC. It is recirculated properly where the BOV return hose is attached to its corresponding portion on the intake pipe.

My 1g BOV vacuum line was originally teed off (old-school style) to MBC when I was running the stock SMIC and 14b turbo. After installing the FMIC & 16g, I still ran this setup and noticed the 'shift lag,' I thought it was because of this teeing off, so I tapped a nipple onto the J-pipe and ran the vacuum line from the BOV straight to the intake mani as it should be, and have the MBC in between this J-pipe nipple and wastegate actuator; I still have the shift lag.

Also could be a loose wastegate flapper or 'sticky' actuator.
Most ball-and-spring MBCs have a small plastic straight-through vacuum fitting that's supposed to go in-line between the MBC and the wastegate actuator, that has a pinhole drilled into the side, to avoid pressurelocking the wastegate open, which would also cause extremely slow/difficult spool.
Testing that's easy though... just take the MBC out of the loop. Run a straight vac line from the j-pipe to the wastegate actuator, and leave your MBC disconnected. Since there's no MBC in the way, it'll let air flow back out the way it came in, instead of having the MBC act like a check valve. If you get full spool after a 'fast' shift by 3Krpm, you might have to enlarge the pressure relief hole on that fitting just a bit.

Interesting, I will definitely keep this in mind and try this out. It's just weird because I'm not getting slow spool at all (spooling fine full boost at 2800-3000 rpm) as long as I start from -23 inHg (foot off the throttle); it's just after the shift that the boost is having difficulty going back to 10 psi. I'm running the TurboXS High-performance Boost Controller (fairly new), and it's never acted faulty on me before the install of the FMIC & 16g.



In any case, I'm definitely gonna take off the MBC, run it without it, and follow all lines and reinstall everything, though that will have to wait as my freakin' alternator (yet again, 3rd replacement in past 2 yrs) has failed. I appreciate all the input, and will let everyone know the issue was when it's resolved. I'm also doing a full carpet install as well as repainting my interior again (hopefully with better paint). Any other suggestions would be awesome. thanx.

 

[Talesin]

I hope that was a typo for 'MBC'... running with no CBV/BOV would be a bad thing.

All you need to do for the WG actuator to get the stock 10psi spring rate is a length of vacuum tubing from the nipple on the compressor outlet elbow to the wastegate actuator nipple. About six to twelve inches should do it, shorter being better. Though it won't matter much, with a vacuum system volume that small.

And there's a reason I have an Autozone 'lifetime' alternator. Our cars kill the alt roughly every year, due to the high underhood temperatures. I've gone through one in two months, before. Really not hard to replace, once you get the knack of removing the alternator belt... honestly the hardest part of the whole thing. :b
I'd recommend against painting your interior, for a start. Stock pieces look good enough as-is, and aren't eye-rapingly garish like most of the vinyl paintjobs I've seen.

 

[joe]

I had that problem before. It was because of the MBC that i was using didnt have a bleed hole. (like talesin/john mentioned above)

 

[P M]

I hope that was a typo for 'MBC'... running with no CBV/BOV would be a bad thing.

And there's a reason I have an Autozone 'lifetime' alternator. Our cars kill the alt roughly every year, due to the high underhood temperatures. I've gone through one in two months, before. Really not hard to replace, once you get the knack of removing the alternator belt... honestly the hardest part of the whole thing. :b
I'd recommend against painting your interior, for a start. Stock pieces look good enough as-is, and aren't eye-rapingly garish like most of the vinyl paintjobs I've seen.

... yea i meant MBC. yea, i read about autozone , i'm ###### gonna hit them up too.

As for the interior, my car has a custom paint job; it's two-toned black and white and the interior is tan :-\ because it use to be originally blue, i'm going with a black and white theme to match the outward appearance, and it's too late anyway as i've painted it already . hopefully using high grit sand paper on the vinyl will make the paint stick better; i'll post more pix on my profile when i'm done.

 

[P M]

Problem Solved: MBC was shut all the way tight, so pressure was being trapped between the MBC and the wastegate actuator. This trapped pressure results in the wastegate staying open when it shouldn't be, after shifting gears 'quickly' and causes the 'unresponsive' boost.

So after opening up the MBC from it's sealed position; the 'shift lag' went away; my BOV sound increased substantially (I can actually hear it from inside); but now my vac isn't reading that high at idle as it should (-15 inHg). I will double check these values with DSMLink after I redo my interior. Thanx for the help btw!

 

[Talesin]

Yeah, this is why you need that bleeder vac fitting. It's just a straight-through vacuum hose 'joiner' with a pinhole drilled into the side in the middle, that you put in-line between the MBC and WG actuator. Releases the trapped pressure. Also, make sure the MBC is hooked up in the correct direction... the tighter the MBC is (on a ball and spring) the higher the boost level should be.

Only reason I'd think of the vacuum dropping like that is if you were teed into the BOV actuation line (since it comes straight from the intake manifold, allowing a vacuum leak if that line is 'open' anywhere) for your MBC, and were getting air in through that line from opening the MBC too far.