Well I'm pretty surprised at the signifcant decrease in performance of my 08 GT. I currently have a 100 shot SCT tune from Brenspeed, long tubes, exhaust, intake, etc.

I've had the tune on for about a month and a half now. During the install of the tune/nitrous, I added Brisk two-step colder plugs, KB BAP, and other supporting nitrous mods. For the past month the car has acted like a champ. Driving like stock with no hesitation issues or any other funky habits. Well, last night I took it for a drive to pick up a new grille, and ran like normal. However, on the way home it started to acting jittery. I have a AEM wideband afr guage and it was showing inconsistant and odd conditions. It seems like the car could not find it's normal a/f range. Sometimes it would show ultra rich under normal load, and then jump to ultra lean (17:1-18:1). Other times when I would let of the gas it would go to close loop, and when I put my foot back to accel it would hesitate and jitter.

So I decided to drive it another 70 miles to see if a CEL would trigger and nothing. I'm pretty stumped, but I don't feel safe driving the car with AFR's that lean under normal driving conditions. I'm trying to factor in every variable, but I can't come up with anything concrete.

I'm Brenspeed's tune specific for all my modifications. Has anyone had any aftermarket tune just suddenly go bad?

Could it be a bad o2 sensor? These past two days, the weather has significantly dropped (but that always makes my cars perform better), bad gas (I always use Mobil/Exxon 93 octane)? The car only has 4,000 miles on her, so a lot of things that usually go wrong with higher milage has me stumped.

Any input is appreciated guys.


--Brandon

 

It's possible to get a corrupt file but I would think it would be very unlikely, first off try reloading your tune. If this doesn't work, call your tuner that's your safest bet

 

Yeah, Brenspeed has such a great reputation. I've been so pleased with their business in every aspect. Although it makes me feel a little better that it's possible the file could corrupt.

 

What type of intake do you have? Check the connections of the intake. Is the Mas dirty? Filter dirty? Throttle body dirty? These small items will make the car run like crap all of a sudden.

 

Yeah I really doubt that it's the file itself, like he said check/clean all the connections you can think of and have you tried reloading your tune?

 

These are all good questions. The intake I have is a Demolet Tuneable Induction CF intake from Brenspeed. I would say that it's a little dirty, but the red filter it still clearly visable. Again, the car only has 4,000 miles, so do you really think that the t/b or MAF would be the issue? Of course I will check all of these. What should I use to clean them?



There is NO WAY it's the tune. I loaded my Brenspeed 93 octane n/a tune back on and the car still runs the same.

 

http://forums.bradbarnett.net/showthread.php?t=473591 Somewhat similar, his wife put 87 octane instead of premium. Depending on your mod list try returning to stock tune.

 

I always put in 93 octane though.

 

The first thing I would look at is where the intake tube connects to the throttle body. Then where it connects to the MAS. These come loose sometimes. With a newer cone filter, they are sometimes over oiled, and that oil gets on the MAS. Any auto parts store carry the cleaners needed for each. I would try all these.

 

Man i'm only trying to help...

 

This is true. I checked everything, all sensors are clean, t/b is clean. I will take out my Brisk plugs (which I'm now reading are crap) and put in my OEM HT1's to see if that is the problem.


No I know, and I appreciate it.

 

UPDATE: There is no way it's the plugs. I put my OEM HT1's back in and am still having the same problem.

 

Did you call Brenspeed? Only other thing I can think of is to disconnect the battery for 15 minutes, but i've heard not to do this with a tune. Better to find out first

 

All Brenspeed said was that maybe I possible switched my two front o2 sensors around. HOWEVER they only time I ever disconnected them was when I did my long tubes (5 months ago).

 

A guy on another forum thinks I should set the car back to stock, disconnect the battery for 15 minutes, erase my tune off of my SCT tuner, reload the tune (saved on my computer), and then upload it back to my car. This will rule out file corruption. What do you guys think?

 

I've heard of doing this, didn't know you had your tune saved that makes a difference give it a try

 

UPDATE: I returned the car to stock, deleted, disconnected, and then reflashed my tune. The car does not stall out anymore, but still in 5th gear has this sudden, and very very inconsistant jump to a lean afr or even close loop. I mean, for just a split second. However, you can feel it in the car's performance, as it seems to hesitate.

Brenspeed says that it might be because I accidently switched the front two o2 harnesses during my long tube install. HOWEVER, that was months ago, wouldn't it of acted up initially? So now, I'm more confused than every what to do...

 

No not necessarily. That's kind of like the BBK TB issue, where they work fine for a while and then go ape sh*t throwing codes, try swapping them I don't see how it could hurt anything and you'll find out real quick if that's your problem.

 

True. This is my last resort. Is it possible I got a bad tank of 93 octane? The problem happend about 30 miles after filling up on a full tank.

 

Anything is possible, if you think it's bad gas i'd either A see about draining the tank or B switch to your stock tune to burn the tank off, fill up, burn another, then swap back. As that link I posted shows its very bad for a motor tuned for 93 to run 87, but i'm not sure if that would cause the problems your seeing or not.