Hey Guys,
I've been noticing a lot of shuddering and sputtering at highway speeds and when accelerating gradually at part throttle. The odd time I could not boost over 5-6lbs. I reinstalled the stock airbox and it still does it so I brought it into the dealership and they ran a few tests and couldn't find anything even though when I picked it up I was barely 100 meteres up the road and it started again. Since there is no CEL, they basically told me to drive it until it breaks. They did do an ECM update that was available but it solved nothing, it seems like the clicking in the engine has gotten a bit louder also. OnStar Diagnostics believes it's misfiring and could be a voltage problem and I mentioned that to the dealership and even though I said it was misfiring, they didn't bother to check the spark plugs or coil which seems odd to me. Basically all the tech did was hook it up to a computer and took it out on the road and found nothing. Does anybody know exactly what they can check for? Can they tell if there's a voltage problem, bad injector, valves stickin, etc....? Any info would be appreciated, Car currently has 30K Kms.

 

MAP sensor

 

Shouldn't there be a CEL if it's a sensor? I've been GMS1 since July/10 and drove all winter with no issues, seems odd it would be happening now

 

check ur spark plugs. does it idle rough? if not prob the map

 

do you have a wideband?

 

I'm not very mechanical so I've got no clue how to check my spark plugs or even the tools to do so, and no I do not have a wide band. Shouldn't I be getting a CEL? And I don't know how they couldn't find anything

 

sounds like a fuel issue to me. just a guess. which if it's not happening often probably wont throw a code

 

That's kinda what I'm leaning towards would be either the injectors or valves because the RPMs do not seem to be fluctuating

 

LNF has built in wide band. MAP sensor or spark plug can easily cause these, it usually would throw a code but its human made, doesnt mean it will always work.

map sensor is easy so are plugs, just need socket and screw driver.

 

take it to another dealership. that's bullshit that they can't figure out anything if it really is acting up. like northvibe said it's easy to check these things. you could prob even find a youtube video on how to charge your spark plugs if u needed the help

 

ok, so i guess if hes leaning out it would most def throw a code?

 

Thanks for the info so far guys, it's much appreciated. It seems like it's bogging out when it shudders, wouldn't that be running rich as oppose to lean? I'm not showing any knock so I would assume it's dumping too much fuel. I wish a sensor would go off so they can better diagnose it. I did have a misfire when I first got the car and it immediately threw a code and I had to have the spark plug and coil pack changed in cylinder 3

 

TO me, its sounds like s purge valve issue as if it were stuck open, meaning the car was sucking in fuel fumes or even fuel itself. Reason it would do it at idle and cruise is Vacuum... Its sucking. And if the purge valve is stuck open it wont cause a cel. wut you can do is take it off and check the purge valve, if you can blow through the end and out the other side its bad, or atleast its stuck then.

 

if the cr would be leaning out, there would be a def reason, like say bad 02 sensor or somthing like the maf or map sensor being bad..... So it would more then likely throw a code .. but if it has a vacuum leak or boost leak it could possibly not throw a code!!!!

 

i had a bad evap purge. it was stuck open. only caused a vac leak. on boosted cars it shouldnt effect while boosting.

 

ok first off, the purge valve is used to purge, is op driving in boost no, he states he cant get more boost the 5-6, so yeah.. And while boosting the car will cause pressure tot he evap canister and sensor s and ect, so it could possibly throw a code for that. but this could cause his issue since i had the same issue. and it was my purge valve, ive now replaced around 4

 

not that purge valve... talking about evap. the bov or purve valve i can see that being the issue.

 

It limited me to 5-6lbs a few times and then snapped out of it. The car performs great even at WOT, doesn't seem to miss a beat in that aspect as it stands right now. The only time I notice it is when driving at highway speeds or when gradually accelerating at part throttle. Your theory about a possible Vacuum leak is definitely plausable as most of the time, the problem occurs when I'm at little to no boost. I know this is a newb thing to say but is the purge valve that device connected to the intake? When I had the K&N SRI on I could hear everything a lot more clear, when my boost was limited I noticed my BPV sounded a bit weak but later sounded ok.

 

Check ure endtanks. Lol i blew my hahn ic endtank recently like 3weeks ago.... Lol.. I know the issues with a blown endtank ive had many blow on me in diff cars

 

No. My TMAP pigtail was corroded to **** and failing, same symptoms as you, no CEL. I also blew a hole in my lower hot-side charge piping, no CEL. In both cases it was a P0236 once scanned. If you have OnStar call them and ask them to run a diagnostic, it only takes 30 seconds assuming you don't have an OBD-II.

 

Mine took a **** never showed a CEL just stored it

It actually just happened to mine last saturday. Car shut off on me a couple times too.

 

Im running into similar issues. I'll be crusing not even building boost. Car will just start to buck and missfire then it will refuse to build boost. Doesnt throw a cel but my code scanner will read a p0101 which is maf. I just replaced it. If I clear it, car drives fine until next 50mi cycle it seems.

 

Sounds like your car has a boost leak or a vacuum leak..

 

im getting this issue too.. its annoying driving in traffic.. but like the OP said, car performs amazing at WOT but putting it around blows

 

Exactly, it's very annoying, usually it's a slight hesitation, you can feel it kinda of holding back and then the odd time when you gradually give it fuel, it sputters a bit to get going. It's not bad enough that I can't drive it but all the same I want my car to run like new and it drives me crazy when it doesn't. I'm taking it in soon for inspection and I'll have them check for vac leaks and also the plugs and coil.