Permafried-

So I ruled out traction control issues and the clutch even though it felt like one of those 2 in the first place. The car goes into the dealer tomorrow originally to fix the oil leaks I have since my head was removed and all my intake valves replaced 2 or 3 weeks ago, but now I've got other symptoms that need to be looked into, and they're intermittent. I'm leaning towards a vacuum tank leak (or bad vacuum line), or perhaps the wastegate, definitely doesn't behave like a boost leak. Here's what it's doing:

1. Will hit full boost and slowly drop from 21 PSI back to 0. By slowly I mean in top-end over 4 or 5 seconds, not instantaneous.
2. Sometimes, the car hesitates, boost will go up to 21, back to -5 or so, back up to 5, up to 15, all over the damned place. Sounds like a load of garbage when it does this.

I don't hear air escaping, the turbo has 0 issues spooling up (we confirmed this tonight with 2 of us driving side-by-side and I matted it in 2nd), and when it happens the turbo still sounds fine. The reason I think it's a vacuum leak is because of #1 above, it slowly loses boost, not instantaneous like I'd expect with a boost leak. I'm going to request they look at things in the following order, making sure I'm covering everything (and before people ask the TMAP harness and MAP harness from GMS1 are holding fine):

1. Boost leak test, inspect vacuum tank and vacuum lines. Note: When the valves were replaced the car threw a P2261 just before (BPV stuck closed). They assumes it was due to the loss of boost build-up in the manifold, maybe they were wrong because it cleared itself just before it went in but I told them about it.
2. Inspect the BPV for rips/tears, ensure it's operating correctly.
3. Ensure the wastegate solenoid is functional and it's not sticking open.
4. Inspect MAP/TMAP sensors, boost solenoid and MAF
5. Good luck, I got nothing

The worst thing is, there's 0 codes, 0 pending, fuel trims are fine, everything we checked with a scanner last night checked out fine but it wasn't doing it frequently at all last night, and didn't do it tonight until I drove the hell out of it and then drove it "normal" for 10 minutes to home. One pull in there and it bucked all over the place.

This car is starting to infuriate me, it's in the shop for 2 weeks, with me for 2 weeks and I've had nothing but boost issues with the damned thing short of the intake valves being completely caked up

seeyaass

I read a thread similar to this and it was the BPV spring. Check into that, the person put a washer in the BPV and that solved his problems.

Hope you get everything sorted out!

Permafried-

That's basically one thing we came to conclude at the meet last night, the entire BPV including the spring needs to be looked at after ruling out a boost leak and vacuum tank/leak .

Oh, and thanks, me too, or I'm going to put a grenade in the gas tank and run for the hills .

seeyaass

Lmao, don't do that!

How much boost are you tuned for? If i were you i would put a shim in the BPV, and inspect the rubber condom takes all of 10 minutes, if that fixes your problem, when you go to the dealer you can tell them you know what the issue is.

Permafried-

GMS1 around here runs 21PSI steady, day in and day out, except in the winter, it drops to maybe 19 with the denser air . I've basically written up a list of things for them to check (similar to the post) and since it's going in for the oil leak anyways, I'll let them take a look and put a link to that thread (I found it) in there for reference. I'm too lazy to check it tonight .

The dealer is great at listening, and very thorough so I have confidence if I say check this they will . Their techs also don't hesitate to call GM Tech for input which is a bonus, it said right on my workorder last time they did about the P0236/P2261 and they were instructed to check numerous things including the intake valves .

seeyaass

Sounds like you got a good dealer there bud! Lucky you, lol. I had the dealer by me replace my rear bowtie, and they couldnt even do that without scuffing my trunk up. I had to wax it like 3 times to get it out.

Your dealer seems good though, sure theyll figure it out!!

Permafried-

Yep, no complaints about them, hear too many stories like yours with dealers (my home dealer was like that, I tried different ones in the area for a few years until I found this one). I'll update the thread as the work is completed . Thanks for the quick replies, she goes in early tomorrow!

Edit:

I'll link this here in case anyone searches and comes across the same symptoms so they look into this thread:

https://www.cobaltss.net/forums/2-0l...-fixed-257479/

seeyaass

Sounds good bud keep us posted!

Permafried-

Well dropped it off this morning with my list and in she went. Oil leak was where I thought it was valvecover gasket replaced, the one from 2 weeks ago had a tear. As for the boost loss and hesitation it was the god damned lower TMAP again. Solder joint was breaking from crashing off the AC condenser (they now zip tied it to cold side charge pipe with enough slack to move so it re-routed) even with plastic conduit surrounding it. The good news they had GM Tech on the phone most of the day running a battery of tests, and besides that everything else is in perfect shape no vacuum leaks, no boost leaks, no oil on my sensors, etc. My fuel trims must have been a bit off, did pull after pull on the way home, back to normal.

The **** off that harness was re-done at a different dealer a couple months ago and it already broke the joints. That thing is a pita But as usual this dealer pulled through and again didn't hesitate to get the tech line involved .

seeyaass

That's good to hear man, glad it was a simple fix!

After you did that pull did you still wanna blow it up?

Permafried-

God damn it no

Permafried-

Took the car out for 2 hours tonight and something still doesn't seem right. I'm going to pull the BPV this weekend, and test the vacuum tank out, I still swear I have a vacuum leak somewhere but the TMAP harness fix resolved the "boost all over the place" problem, still not convinced the "boost is going somewhere really slowly at WOT, 1/2 throttle, etc it doesn't matter" issue is resolved though. Sometimes it pulls fine, few minutes later it hesitates. May as well rule out the simple things myself first .

PrincessTurbo

get a piece of hose and delete the vaccum tank and see how it runs ...


Seen a few tanks crack probably from constant heat and cooling cycles and cheap plastic.

rukkee

iTrader: (3)

IF you had a vacuum leak wouldn't you be able to see it at idle on the guage? Mine idles at -20 or so but if it had a vacuum leak i would imagine it would show somewhere closer to -5 ....or -10 .

Permafried-

Yep that's on my agenda for the weekend. May as well remove it from the equation and see what happens. Worst case the car runs the same .

I'm pretty sure it's sitting where it normally would (converting to kPa), I'll see if someone local can telll me where theirs sits in kPa but I'm pretty sure mine's sitting where it always has.

The BPV sounds to be working fine, I can hear it spitting and sneezing like it always has, but there's one case that's bugging the hell out of me which happens very irratically, not every time I drive it, but I can feel it when it does. The boost dropping off makes more sense to me.

I go WOT in 2nd gear, the turbo spools up, hits 21PSI and holds. The exhaust sounds normal and the RPM rise slowly (so not cluch slip) and the car feels like it has absolutely no go at all. It's making a lot of noise and doing not much of anything . Out of throttle, back in and it pulls normal. Something has to be staying open for that to happen which is why I'm going to start with vacuum and go from there .

EDIT:

I had someone suggest a clogged/partially clogged cat. Never thought of that one and one of the side-effects is "hitting the gas and not going any faster" which is one symptom I have. The other, losing boost like mad at high RPM could be a result of excessive back pressure in the exhaust manifold and the turbo is fighting it. With my valves leaking like hell for god knows how long, the potential would be there to have damaged it. I'll put that one on my list .

09 ss/tc

This is my first post and I know this is almost a month late, but my cobalt does something similar to this. When im at the track racing and I take it past 5 thousand rpms the car seems like it cutting out, like the boost is not holding past that rpm or something. My car is dead stock by the way and i was wondering if your cars did the same thing when it was stock.

Chris@CTA

iTrader: (1)

I'm not really sure if this is the same issue, but for the first time, hot weather running A/C, boost wouldn't go over 5psi. Shut the car off, turn it back on after about 5 minutes, all is fine and it hasn't happened since. FYI, I'm running stock PCM, no S1 or aftermarket tune. I do however, have an Injen intake and hot side pipe.

One other thing, engine seems to build power in stages instead of being linear. I can feel 3 distinct phases, like low, medium and high speed phases as the engine rpms increase, revs appear to cut out at 6200rpm. Boost gauge shows relatively steady boost, but I can't really say for sure since I have to concentrate on what is in front of me. Need to take a video of the boost gauge when at full throttle to confirm.

Permafried-

I can't remember the boost drop-off when stock, I know with GMS1 it drops like a bomb at 5500RPM and continues through to 6500.

I didn't have the A/C on at the time, but now that you mention it, if you're sitting in your driveway just after starting the car and turn the A/C on, does your vacuum decrease by ~10kpa (eh 1 or 2 PSI for those with the PSI gauge)? I noticed this around the same time this thread went up.

The car hasn't done it since, and my friends with an SC did the exact same thing around the same time mine was. People are saying humidity was to blame, which I'd be ok with if I wasn't at full boost .

Chris@CTA

iTrader: (1)

I'll try to check for the condition with A/C on, but I think that's normal for the vacuum to drop when at idle since the A/C is putting a load on the engine and the throttle plate is still in the shut or minimum position?

ATLsilverSS

iTrader: (4)

it's normal for vacuum to drop to about -10kpa with the a/c on