MajorCB

I'm trying to figure out the source of a boost issue that I have been having for some time now... The issue doesn't really happen when I am pressing the gas for stronger acceleration. The issue mainly occurs when I am trying to cruise with little to no gas.

during this time, the system seems to not know whether to boost me, or sends exhaust gas or something back into the system which causes a significant stutter , enough for the car to lurch forwards as if under breaking, but only for a moment before it surges back into boost again. Its a repetitive process. It doesn't happen EVERY day, but it does most days..

Possible Sources: Recently changed / upgraded intercooler(only) , no changes in MAF location or charge piping minus the connections at the intercooler.

Wiring / ECU : have had the Chevy upgraded HBar sensors upgraded and tune with an HP tune above that for 2 years.. no issues with that at all until the last 3 months -- could the HBar sensors go bad?

Re-wired the lower Sensor near intercooler due to a bad initial wiring job -- perhaps my job sucked as well?

replaced the upgraded BPV for the stock BPV.

Could the Tune be losing its strength from 2 years ago?

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my plan: check the system for leaks from intake to intercooler... check the turbo for tightness on clamp fittings.. check wiring...(again).... check the stock BPV for issues... if this doesn't work.. what else could it be.. any suggestions?

thanks everyone.

MajorCB

Also just to clear this up ahead of time -- During this period, I've had no CEL's an no codes ..

Snail_SS

iTrader: (3)

Hmm kinda sounds like what I was having ill look for my thread and link it here maybe it helps. What I ended up replacing was the bpv solenoid that is located on the intake mani

MajorCB

ok thanks.. I'm not entirely sure where the solenoid is for that on the manifold. a visual description would be great if you could. I know where the Evap Solenoid is however.

Snail_SS

iTrader: (3)

Well it has a connector and 3 vaccum lines going to it. One goes to the bpv actually

Sl0wbaltSS

Cobalts have a EGR?

MajorCB

non turbo one's I guess have the EGR valves.. but I was trying to describe the feeling .. of boost to the feeling of stutter or instantaneous loss of boost.. a purge of sorts.. causing the stuttering feeling of boost surge to what feels like engine breaking , or purge causing the car to stutter or lurch forwards.. then surge again...

hard to describe I guess.. a video on the psi or boost guage would probably be best..

I went under the hood and "THINK" I found the first issue with the intake... the modified ZZP piping was very difficult to deal with and found fitting somewhat difficult on the intake. it looks like the link between the air box and the piping wasn't spaced properly ( possibly my fault ) but the stiffness of the piping I think torqued the air box enough to cause a small air gap to form--thus the system is now compromised.

So I too the entire thing apart and adjusted the pipe with the MAF and adjusted the metal fresh air tube for the PCV and I think that hopefully will fix the problem...

will update tomorrow.

tomj77

iTrader: (2)

well ill answer some questions that were asked. turbo cobalt does not have egr valve. Tunes do not go bad over time, ur ecu can go bad, but tune is just software on the ecu, if its good when u put it in, it will stay good. an air leak in the intake pipe will probably not cause the issue ur getting, may be wrong, but I doubt it. im gonna guess boost leak somewhere, do a boost leak test. since it happened after u installed intercooler.

Sl0wbaltSS

Too strong of a spring for the little amount of boost going in?

hotrdr

I have the same problem! Doing 60 usually up a little hill..then let off a very little bit at the top to maintain speed and it sounds like the bpv stutters for a second. It shakes the car and scares the Crap out of you. I have a stock bpv and was thinking of changing it but it sounds like it still did it on 2 in your car. Let me know what you find. I'll keep looking.

user 72239

iTrader: (4)

bypass the vacuum solenoid on the intake mani by putting your bypass valve hose directly to the intake manifold. Dont forget to plug the hose from the lower CP though so you dont create a vacuum leak.

Drive around for awhile to see if that is the problem.

MajorCB

Hey all..

well some updates.. so I found one leak, it was in the intake hose where the ZZP upgrade hose mated to the plastic air box... I needed to adjust the length on the airbox side as well as the fresh-air inlet and that cleaned up the closed system, no more leaks that I can see at the moment... but im not fully done checking..

on the other side of things.. the MFD is going in and out of showing boost .. to clarify what I mean, when I switch it over to see the digital boost guage, it says "no data" .. I turn the car off.. then back on... and it shows boost data..

however driving tonight.. I could easily see that I was surging boost significantly in 1st which isnt normal.. 4th and 5th gears when gently adding boost it would begin to spike then drop rapidly..

still makes me wonder about a leak.. but ive checked the hot / cold pipe connections where I replaced the intercooler and all is well there..

so.. its not the tune...

its solenoid potentially..
possibly still a leak


but the randomness of the boosting when not even really putting pressure on the system is what is throwing me.. if there's a leak.. shouldnt it not boost? .. I think this is why I think there is something else going on.. but I dont want to over think it either.

MajorCB

are there some visual directions for this procedure? ... havent done it before

MajorCB

slowbalt.. Im back to the stock BPV.. cant figure this would be an issue.. unless I mounted it back up wrong.. but it seems fairly idiot proof ? ... factory spring seems like it goes only one way on that setup..

ECaulk

iTrader: (6)

Check your re-wire on the MAP, if the RPD is saying "no data" for boost/vac reading its not getting good signal from the MAP sensor

MajorCB

bout to ask the dumb question of the day.. but which map sensor is responsible for the MFD ad the boost / vacumn ... is it the one down at the bottom of the intercooler.. I think on the cold side of the charge piping... that's the one I did re-wire.. so I assume that's the one you meant.. I havent touched anything else.

is there a way to tell if the sensor itself is bad by chance? in case it isnt the wiring

tomj77

iTrader: (2)

Did u do a actual boost leak test with a tester or just look at ur connections and tighten them?

MajorCB

Tom,

i'll be doing that this weekend. I think the intake was part of the real problem..... but in the mean time..

if under WOT I get Zero boost loss, yet under significantly less throttle the boost spikes and doesn't really hold a consistent value, is a boost leak really the issue there?

I have tried numerous times to recreate a loss of boost under WOT, and I get nothing.. its only under modest throttle during 2,000 - 3500 RPM shifts .. or under 4th and 5th gear modest throttle pulls from say 50 - 60 mph. this is where I see the biggest boost spiking and or stuttering.. though a lot less since the intake tube leak was solved.

but I will check for leaks fully again.. but in the mean time.. just trying to work it out in my head.. if there is a leak.. I would think I should see it even under WOT.. unless its so miniscule that the amount of boost over compensates the tiny leak.. and it only shows up when Im asking it to boost modestly? say between 2-10lbs.... that's where I see the largest issues.. if I go hard bore.. 20-25lbs right away.. I don't see any hesitation.

ECaulk

iTrader: (6)

This car is dry by wire, so for any given throttle position the ECU goes oh the driver wants this much power, and when you dont keep pushing down on the throttle the ECU goes oh the driver doesnt want more power so i'm going to slowly let it down. Also the KO4 can push more air then the ECU calls for at WOT for most tunes (guessing you're at 24psi) which will mask a boost leak. Hell I had a damn good leak on my upper charge pipe that didnt show up till I put 20psi on it, i was still spiking to 28-29psi (KO4+ and 6000ft above sea level)

MajorCB

good points Ecaulk, thanks for the post. I will definitely be doing the boost leak test this weekend.. tonight's drive with air temps IVO 60F, dry air, and high Barometric pressure 30.00in .. I had no stuttering.

by contrast a week ago.. hotter temps, higher RH, and slightly lower pressure.. I was getting significant stuttering.. but also because of the intake issue..


so I think the thing to do.. obviously, is boost leak test it.. start from there.. then check connections etc. if its not that.. then what would be the NEXT most likely cause of this issue if not a leak.

thanks again for your guys' inputs.

iboost

iTrader: (16)

I'd say, if you have HPT than to log for a tuner or your tuner and let them see what's going on with it. Maybe your MAF?

tomj77

iTrader: (2)

U can't really check boost leak that way, any little movement of ur foot on the gas will cause u to see different psi on the gauge. U most likely won't see a boost leak on the gauge at wot either unless it's huge leak. The turbo is just spinning faster to compensate for the leak. Boost leak test this weekend will tell the story

MajorCB

agreed tomj ...

snoftall

MajorCB, it would be GREATLY appreciated if you can keep updating this thread with what you find. I've been experiencing the EXACT same intermittent problem you've described for the last year with my 2010. The only difference is that it does not happen every day, or even every month...it is very random and I haven't been able to recreate the problem. Also, this car only gets used for 6 months of the year and during these 6 months, I probably spend 3 months offshore so it has been difficult for me to do any testing or check items.

I have noticed that when it happens under light throttle in second/third, it happens more frequently when the car is still "cold" or within the first 10-15 minutes after start-up. I've also noticed that once it happens, it doesn't immediately happen again...it may happen a few days later or a few months later....again, completely random.

I've only experienced it twice while in fourth/fifth and its been while cruising on the highway/freeway with cruise control active. Both instances, the car started to go up a small hill/grade and the cruise control causes applies light throttle and the boost to go up to ~1-2psi and then it occurs. Both times after this occurred, I geared down to 4th and when I tried accelerating it would not boost past 3psi. Then I would let off the gas again and when I tried accelerating again, it would boost normal and the issue was gone. During one of these instances, I noticed that the boost gauge screen on the RPD showed "no data available" for a split second and then returned. Also, the g-force screen also showed no data during this same occurrence. There was one other time I've noticed the RPD show "no data available" for the boost screen but that was while sitting in a parking lot just before I turned the car off. When I started it back up again it displayed fine.

No codes have been thrown during these cases. I have an interceptor gauge installed and I haven't noticed any misfires or anything out of the norm on it. The only thing I've noticed is on my RPD I notice the spark advance bounces around quite a bit when this happens; there is no knock picked up though and like I said, no codes have been thrown.

I'm very interested to see what you find out to see if it can apply to my situation.

MajorCB

I will do my best to keep it updated.. sounds like you and I have pretty similar issues.. I am planning on doing the boost leak test ( just to Sherlock Holmes my way out of the most usual issues with peoples boost problems ) .. once that is complete, I will assume it could be a wiring connection somewhere or maybe a bad sensor or something.. but until then I want to start at the beginning...

for me , like you, RPD 'no data displayed' has happened.. Ive gotten the same stutter at similar areas of boost , usually between 2-10lbs under modest cruise between 45-65mph

so we'll see!