I have what appears to be a programming problem. Not to go into too long of a description, but the problem is that when I accelerate at a rate any less then WOT, the engine studders between 2500-4500rpm. The studder feels like when fuel injectors go bad, but the car only has 8000miles on it.

I have stage 2, with ALL of the reflash updates. I have taken it to 3 dealerships, and have even talked to GM customerservice, whom has talked with the stage 2 engineers, and still no one knows a solution. In the end, GM told me there is nothing wrong with it, but I know that isnt true, and the technicians at the dealership even disagree with GM's assesment. But I have no other alternative except lemonlaw, so I have decided to just take the car to a local shop that uses HPtuners.

So my question is; if this problem I am having, is becuase the stage2 tune is sloppy, or perhaps my computer is just confused from its sensors or whatever it may be, can HPtuners iron out all the kinks? For example; if the injectors are being told to cut fuel supply in and out, can HPtuners rewrite the code that tells the injectors to spray?

Obvioulsy I don't know much about tuning, but I want to have an idea of what to expect when I go into the shop..

Thanks for any help! I know the description is vague. I appreciate any responses.

 

I know the old stage 2 tunes had studder points. But it all should have been fixed with the latest patch that they load. It sounds like you might have more of a mechanical problem, but if it is something like your getting KR in that area "which can causes hesitation" then you can fix it with HPT. My guess is to check you spark plugs, run fuel system cleaner through twice, and see if that works. Also I have been getting hesitation from a bad clutch so if you think your clutch is close to being gone then that can cause it to. Good luck

 

i need to log my car when it does this to find out what it is.

it might be the simple fact that it has negative timing down low. i have had it studder at wot in third gear a couple times. never could figure that one out.

i'll let you know what i find out on the down low rpm studder.


FYI, mine is an 07, and no the latest "tune" doesn't fix it.

 

I would start by replacing the fuel filter. then go from there.

 

couple things that a cheap and easy.

New plugs and hit the MAF sensor with some brake cleaner, especially if you have an aftermarket filter.

I had the same problem and these two fixed it for me. Those copper plugs don't last forever like the stock platinum ones.

 

Thanks for the suggestions guys.. I have recently gotten BBB involved, but if they cant get anything done, then I will try to fix it myself..


I'm losing patience though because I just got my Corsa exhaust in 2 days ago, and I don't want to put it on the car until the problem is resolved. So I will just have to stare and drool over that shiny tip..

 

If you arent at WOT when it happens, you may be running the car through its timing map, making it drastically change timing advance, which would give you the surging. You could change it with HPTuners but you will either end up in a power loss or lower fuel mileage.

Edit: I'll draw up a pic in a sec.

Ok, this is a really crude paint drawing so bear with me...

normally, when you go wide open throttle, you run through the spark map like this:



Note there isn't much of a variation in degrees of timing advance thats applied in that situation.

Here is probably what you are forcing the PCM to do when you acclerate hard but not enough to put the car into power enrichment mode:



Note the higher variation in timing as the PCM literally is searching for a correct value, but is constantly changing it due to rapidly increasing rpms, with a slow climb in airflow.

Its a poor drawing and explanation, but its kinda hard to explain exactly what its doing without seeing a log of the vehicle's air/fuel ratio, knock sensor reading, and timing advancement.

 

I feel that sometimes in my car, under those light throttle, higher RPM accel. When you step down a little more, but not all the way, you can feel the car add or pull timing sometimes.

 

This all makes sense.. ALOT of sense..

But, lately the jerking has gotten much worse, and at times it feels like the car is going to stall out. And in the past couple of days, it has started to have the hesitations even during WOT. It isn't as frequent, but there are many times that it has hiccuped with the pedal to the floor.

Thank you Witt, that was well explained.

Is there any way to reduce how much trouble its having, if this is the problem?

 

In all honesty, it could really be anything. You need to find someone local that is half decent with hptuners to scan knock values, timing advancement, and possibly commanded pulse width. You could even do it yourself with HPT or an interceptor and report your results to any popular tuning forum.

The possible causes are many so it needs narrowed down a bit further by ruling out some of the obvious such as knock.

The car in a stock and GM stage 2 form does exibit a small of amount of surging in my opinion, but not as severe as you describe. The possible cause I gave in my earlier post is probably exaggerating an actual problem you are having. If you determine and fix the problem, hopefully there won't be a need to edit the tune.

An aeroforce interceptor gauge is a great investment imo and you will probably discover your problem by monitoring common values. Even if you don't have a problem, its a very useful gauge as its the only realistic means of monitoring knock retard, intake air temperatures, or any other PCM value without having to have a laptop open.