So, if you tried helping me before, thx, but the problem is yet to be solved. Did a bunch of tests, tried a few different things, put it back on the dyno and still have the same loss in HP.

I need HELP guys!!!!

Myself and my tuner are completely stumped.

Here is the most recent outcome via an email to HPtuners via my tuner at SpeedDreams:

Have a 2005 Cobalt ss/sc that's way down on power. Car ran great for months, came in last week and dynoed 50 wheel horsepower less all of a sudden. Vehicle passed compression, leak-down and injector flow testing. Tune is still where I want it on the timing/af.
So far this is what has been tried to fix the problem:
-Exhaust has been upgraded to a lt header and catless 3"
-Spark plugs have been switched for 1 heat range colder plugs
-Supercharger has been verified to produce the same 15.5 psi
-Torque is only off by 10-15 ft. lbs.
-IAT's appear to be within range and heat exchanger is flowing coolant
-Hp curve is significantly affected being 5-19% lower at all rpms

Here is the log from our last try on the dyno recorded on HPTuners:
http://www.turboninjas.com/gallery/d.../jjrun022_hpl?

Here is the actual dyno results: blue is original 262whp dyno, Red is current:



I'm really at a loss here guys. Other than the loss of power the car seems normal. I don't know what to think or where to go from here.....

 

Have you done the boost bypass mod??

 

no....

 

Do you have any KR? That second dyno looks all bumpy. How does it idle? Missing @ WOT?

 

WOW thats bad! Ok not to state the obvious but did you do ANYTHING differently before it crapped out?

 

No signs of KR at all. Second dyno probably wasn't smoothed as much as the first. Did get some missfire codes, but not until exhaust was done, so we assumed it was becasue of that and retuned it slightly to compensate. The power was gone before exhaust was done (i.e. Exhaust was done thinking it might have been a clogged cat, but it wasn't)

Not that I can think of.

Tried an octanebooster/fuel system cleaner. But power was normal after that, it was about a month later that it started acting up.

Missed a shift once racing.

Thats about it.

 

probably a different dyno calibration

 

That's really strange man! I don't know what to say about that one.

 

Same dyno, and it has not been changed at all. No other cars have had this issue, and there has been an SRT on that dam thing 8 times in the past 6 months without an issue.

 

SO one day you car was driving fine the next it felt slow ?

 

pretty much.

 

Whoa why are you only producing

-Supercharger has been verified to produce the same 15.5 psi

with a 2.7 ? i run a 2.8 and i get 16-17 depending on the temp

 

#4 piston maybe

 

I'm at 5600' here in Albuquerque.


Motor is solid. If a piston or rings or valves were bad it would have shown up in either the compression test or the leakdown.

 

ohh ......

 

Anyone know where our boost is read from? Because I thought it was wierd that after I did exhaust my boost didn't drop any. It still sits consistent at 15.5, now it is a little slower getting up to it since I've done exhaust, but I thought I was supposed to lose some boost pressure after I did exhaust.

 

maybe your elvation has something to do with not losing the boost

 

Any codes at all?

 

would a faulty o2 sensor figure into all of that, i know you said about 15.5 psi which means its probably not a clogged cat, but when you put in your header, did you mess with the o2 sensor at all?

 

no codes (at first) Recieved a missfire code and O2 codes after exhaust was done, but assumed taht was related to exhaust and not the original problem. So no codes at original power loss.

I did full exhaust, so yes the o2's were moved but then placed back. Rear O2 has been turned off since exhaust was done.

 

K20 swap?

 

Well the only thing I can sugest is your gonna have to do one of 2 things.

#1 get another Cobalt and don't break this one.

OR

#2 Change your sig with the lower hp #'s.




Ok I'm sorry bad jokes I know

Ok some off the top of my head ideas...
Belts not slipping right? Injectors aren't clogged? Have you tried to disconnect the battery and reconnect it and see if it re-sets itself? You said you used a fuel cleaner, what brand and what type EXACTLY! Some have ben known to damage fuel pumps. You guys did check the fuel presure right? Since your catless have you tried unhooking the rest of the system and seeing if it does anything. A bananna in the tail pipe all this time would suck!

 

Maybe I wasn't clear, the exhaust was done after the problem arose because some thought it might be a clogged cat. The entire exhaust system has been replaced. It dodn't solve anything.

 

My bad, sorry. How bout the rest of the stuff I asked?

 

Doesn't seem to have belt slip if it was slipping it wouldn't be boosting the same.
Injectors were flow tested which was stated above.
Haven't tried disconnecting the battery, but the ecu has been reflashed several times with HPTuners, so I don't think that would make a difference.
And I can't remember which fuel cleaner I used, but if fuel pressure was off I would think we'd see a change in the af readings, but they are staying consistent around 11.8-12.2 at WOT.