Long story short...Installed a Hahn 3' catless downpipe and was very happy with the gains (butt dyno) and sound improvement. Turbo seemed to spool faster and gained some power up top as well..loving it. Had front cover gasket replaced by Cevy dealership for small leak, get the car back and the gains are gone! car feels slower than when I dropped it off. Anyways I was not sure what was going on so after some searching I reset the ECU and VOILA the gains are back. Everything was good for about three weeks or so and now it seems that the car learned down again!. I will not be tuned other than GMS1 until warranty is up. Any input, advice, questions, flames for being a noob, are all welcome.

P.S. HHR SS, 11,000 miles, GMS1, Forge BPV yellow spring.

 

The only "gain" you can get without a tune is the car being able to reach top HP slightly more quickly.

The stock tune will still never let you pass top HP, so you're gains are largely imaginary.

Get a K&N SRI, and read up on here for the install (specifically, how to position the filter for the least fuel trim skew). That will really make her feel like a new car (or at least sound like one).

Forge BPV wouldn't hurt either.

 

I have the GMS1 and a Forge BPV. I was under the impression that the GMS1 disabled the "learndown" as it is commonly refered to, and I did feel gains from the downpipe. I have an HHR SS so the intake is not an option...same motor though.

 

The nanny ("learn down") is still very much there with the GMS1, however the limits for things like desired torque, air loads, timing, ect ect, are just raised a bit to allow more power over stock.

 

So when I reset the ECU the gains from the downpipe are evident and then eventualy learned out?

 

If you feel a severe loss of power until you reset it, it is probably throwing a code. Likely P0236, which means there's something up with your lower MAP sensor. Check codes before resetting. If you keep resetting, you will never know what's wrong.

 

I appreciate the input guys. I think I am going to have the Chevy dealer look for codes and/or reflash the GMS1 tune to see if that solves the problem.

 

Codes are where it's at!

 

Do not reflash. Read codes. This ECU is quite good about telling you what the problem is. It's just that people don't bother reading it, and interpreting the codes.

 

Is there a possibility for stored codes even if I don't have a CEL on?

 

yes

 

It would seem weird that the learn down would take 3 weeks to drop the power down ...... unless you dont drive it much at all . There has to be something else going on IMHO.

 

get a hp tuner tune

 

Yeah I know...I'll get there eventually. With the timing cover gasket needing replacement at 10,500 miles I want to hold on to the warranty for one more year just in case. I also want full bolt-ons first.

 

Oh wow. Must have been a faulty gasket or it was incorrectly torqued from factory. Those usually don't go bad...atleast not for a long time.

 

its not the car its the butt dyno! lol but whats your boost normally? my car use to be hit or miss with the power a year ago but this is not limp mode, and it stopped doing it.

 

Usually 18-20 psi. The psi seems to stay the same even when I am perceiving the power loss.

 

I was not too happy about it but it was covered under warranty. I noticed the power loss right after the gasket was replaced...wonder if they did something wrong. I'm not sure if they disconnect the ecu or other sensors for the gasket replacement.