MR.PONTIAC

Hello Fellow Cobalt Owners,

I have had a problem with my SS S/C from day one. I've run searches on this several times in the past only to never truely find the solution. For reference, my 2006 Cobalt SS is a GMPP Stage 2 car otherwise unmodified.

My problem is a hesitation under acceleration. Moderate to mid-level throttle, this hesitation feels like a misfire but has never caused a check engine light in its 36,000 miles. The feeling seems to clear up once I get the rpms up enough. The feeling magnifies once you get some weight in the car. This is not the low speed idle surge.

This problem also existed before the Stage 2 install. I know this for certain seeing as how I thought it was a programming issue that the Stage 2 tune would clear up once it was installed. The Stage 2 was installed at around 7K miles.

My Cobalt has had several items replaced in attempt to solve the problem; both exhaust sensors, the ECM, and the entire engine.

Being that I am a Chevrolet dealer, I have had all of GM's resources at my disposal, so I can't blame myself for not trying hard enough!

One strange item to point out was after the new engine was put in. When we called to get authorization for the Stage 2 tune from GM, they said that it no longer requires one, and yet my car still revs up to 7K without fuel cutoff like the tune is supposed to allow.

None the less, tune or not, this car has never run right.

I've since heard of some people saying that colder plugs have helped, but not much else.

Has anyone been able to resolve their hesitation issue?

Thank you,

~Lew

EceSSiveMod

could easily just be clutch slip....

MR.PONTIAC

It's not.

The clutch looked like new when we took the engine out.

EceSSiveMod

could be misfire....mine did that when my plugs were bad

also first gear does buck alot even u move ur foot like a mm to much

MR.PONTIAC

Sure would, but this is every gear at any speed.

Plugs looked good too when we checked them.

TommySSSC

check the gap of your plugs, i had it pretty bad after my 60s went in and my gap was too open. also noticed some of my fuses were loose, make sure there all snug in and none of them are out. get some iridiums

blazinbaltss

i had the exact same problem and i took it to gm today and they said the computer was messed up but also i had a valve gasket broke so try those to for sure man trust me i kno theres nothin on her for that type of problem but mine jus happened

Coblasts

When you Replaced the motor all the original parts went back on ,pcm,Blower etc.
Try unplugging a O2 sensor and going for a rip because this will put the car into a closed loop.
And see if you have the same thing(closed loop ignores most of the sensors and will help you eliminate some of those.
Is your pump for the after cooler working ? running backwards.

Just putting ideas out there.

MR.PONTIAC

You're correct. The engine swap used the same blower, injectors, ECM, etc.

The ECM was later changed however.

Our regional service rep had run the car in closed loop and found the car to run smoother, though I wasn't in the car at the time he tested this. Since all the sensors have been replaced, why would it still run this way?

As for the cooler pump, this happens at all engine temps and not just when the engine gets up to normal opperating temperature.

Thanks for the input! Please keep the ideas coming. I'm hoping we can solve this for good!

EdCobaltSS

Throttle body hesitation possibly., or a tps

rukkee

iTrader: (3)

Did the techline say you dont need a VCI number for the stage tune , or they didn't send you the tune at all? I would disable torque managment with HPtuners and see if the thing is bleeding boost or pulling timing at some point under load.

Coblasts

So the facts.

1)At around the same rpm(4000)
2)Operating temp doesnt matter
3)All the sensors have been replaced
4)Motor has been replaced
5)ECM replaced
6) Runs better in closed loop

Whats happening to the boost when its flutterng ?
Is it holding steady or bouncing around ?

The Tech 2 showing misfires on a certain cylinder ?

Lets keep adding to the list and we will narrow it down eventually.

How about a bad TPS causing to much fuel to be injected fouling the plugs and once the revs get up alittle the plug clean up and it runs good again.

rrutter81

Number of things it sounds like,

If it is only 4K RPM then you have an issue with your ECM......

However!

It could be that once you pass 4k you dont notice the misfires that are occuring, which would mean either plugs, or wires. Plugs are more likely to go bad.

Here is the unlikely event I am wrong though....
You have a leak somewhere on your intake causing the hesitation which is quite possible.


Im just going from most common problems to least good luck.

MR.PONTIAC

The boost holds steady, unwavered by the hesitation.

Sadly, no.

From what I've gathered, the accelerator pedal acts as the TPS, according to the sheets I've looked at. Both the stock pedal and my current GM accessory accelerator pedal have had the hesitation.

Both. My tech called them twice to get the same answer of that there was no special tune any longer required with the Stage 2 upgrade. When I first had it done a year and a half ago there was, but this could be a running change.

It's not just at 4K rpm though, it's happening everywhere. It's more of a throttle postion than a specific rpm range. I've been able to hold my throttle steady in one spot in second and third gear almost all the way to 6K rpm with the stuttering happening. Plus, the ECM has been replaced already.

Please keep the idea coming though!

rnjmur

There have been threads on this before, and it is not per-say a "problem". The reason this occurs is because of the GM tune. If you get the car tuned you can take out all the crazy peaks that are caused during part-throttle acceleration and that is what is causing your problem. No matter how much you keep replacing, you will never fix the problem unless you get it tuned. If you need proof of what is happeneing get HP tuners or something else you can use to log and then do some part throttle pulls... you should see that the AFR is all screwy and you should also see the IDC do the same thing. The other plus is that even if for some reason that is not what is causing the problem, you should at least be able to look at the logs to see what is causing the problem.

rrutter81

Thats VERY specific!

You have a leak somewhere where in the intake(very likely). OR (very unlikely) your TB is screwed.

Id check anywhere air goes in,
supercharger mount, gaskets, intake etc. Anything to do with air going in to the engine, even MAF.

MR.PONTIAC

If it is, in fact, a programming issue, why wouldn't have GM Technical Assistance been able to tell me this? They have had several running parameter shots taken from the Tech2 sent to them when the car was doing the hesitation. If there were any irregularities, they should have been able to compare it with a "good" running Cobalt SS.

I still believe you're right that it is in the tune seeing as how it hasn't thrown a CEL, but other than buying an expensive programmer and playing with the electronics myself, there's gotta be a better way, eh?

Could be, but most, if not all, of the gaskets and other items you mentioned are new from the engine swap.

rnjmur

Surely you should be able to find someone in WI who has HPtuners and could do some logging for you. Worst case you would have to pay for the credits, $100 or so. I don't see any way to try and get to the bottom of the issue without getting logging done to see what is causing the hesitation. As far as the Tech2 - i don't know what kind of logging the Tech2 does so I am not sure what information they are able to pull out using it.

lil_kano

clogged cat maybe?

I know it has lowmileage but maybe it wasn't broken in right.

MR.PONTIAC

Bought it new, so I know how it has been driven. It's been broken in properly.

We've also done two exhaust pressure tests that checked out fine.

lil_kano

In that case seeing that all sensors were changed and the car ran "good" in an open loop then it is dealing with programming. The vehicle needs a tune when changing pullies and injectors. There is no way GM can say no to that.

It makes sense because open loop means its not tryign to read for much and just going for it.

Has it ever doen it at WOT?

MR.PONTIAC

Not as I recall.

To be honest, I'm rarely ever at WOT.

I'll have to try that again to see.

jester

Maybe it just feels hesitant cause your not in your t/a.......


ok yea yea yea I know... Im just ******* with you guys... my forums down til 2:30

lil_kano

Yeah because at WOT the car goes into Open Loop.

blackjack hotrods

What kind of air filter do you have? I would assume that the MAF sensor has been checked but if not you may want to check it. I have seen oiled air filters cause a slightly foiled MAF sensor. Not bad enough to set a light but bad enough to feel in the performance.