About 5 months ago I had my C6 with corsa sports, kooks headers, cats, and callaway intake tuned at MTI in Houston, Texas. Since then I have felt a minor decrease in power and throttle response. Is this a common matter or is it just me being rediculous and getting immune to the power? How often do you tune your car? How long does it usually last that way?

Also I have noticed my exhaust tone change a little bit from low RPMS like 1500-3000. It doesnt sound as crisp as it used to. Is it normal for the corsa system to rattle as mine does quite often?

Sorry for all the questions, but thanks in advance for answers.

 

The tune is always the same. Some parameters change though. After ingesting oil for a few years, hot spots form in the combustion chamber and on the tops of pistons. This can lead to timing being pulled from an increase in knock retard. I pulled my heads several times to upgrade and each time I saw a fair amount of carbon build up. I removed the heads to port them at 1000 miles, again at 5000 miles for a compression bump, again at 7500 for the new LS3 heads, and again at 8800 to check clearances and port a little. Each time was a surprise to me with the amount accumulated. If you have 25k, I would imaging there are lots of timing spots on the curve where you loose 3 degrees and hence 9-10hp and TQ. I will be pulling them again at 11,500 in a few weeks to mill and flycut along with a competition valve job and exhaust port work. I will be as new as far as removing the carbon deposits. I will snap a few shots and post a how-to with the project with a big thread. Basically I want to use a big cam next.

Other variables are damaged spark plugs, bad gas, compression droping from rings wearing or being damaged...ect.

A scan of the car with HPtuners would tell you everything that is going on. You should ask MTI if they wouldnt mind scanning it for a diagnosis without getting raped.

Head/cam installs also reset the clock for a lot of what I was describing.

Hope this helps.

 

How many miles on the car and on the tune?

 

I'd take it back to MTI and do a dyno run and compare with the dyno when it was tuned. A tune (ecm program) doesn't go away or degrade, it stays there unless someone goes in and changes it.

A car can lose power for many reasons, spark knock, sensor problem ... just going to need to put a scanner on it and see what's happening. A good dyno operator can watch all the data and see what's going on. Maybe they bumped the timing up too much and it's knocking a bit, an rattle such as an exhaust rattle can trick the ecm to think the engine is knocking. That will all show up on a scanner.

 

w/Spin on this.

Could also be carbon build-up in the TB. Recommend run a few tanks w/FI Cleaner then clean your MAF sensor.

 

You've probably just gotten used to it and are now ready for the next mod!

 

It's true, you do get used to it. You are ready for the next jump...

 

A tune should last indefinitely (or until your next round of mods ). It's not like the old days where you set timing and dwell, and had points that wore and vacuum advance that got out of whack.

Like SpinMonster said, oil ingestion probably has something to do with it. What you said is also true... you do get used to the power.

Can't help you about the Corsas. It sounds like something might be loose, or maybe a bent heat shield. Have you had any CELs? Blown catalytic converters will rattle.