Here is my situation:

I have an SCT 4 Position Chip with three tunes. All mail order from MD. Never had a problem until today.

While driving, I noticed a really strange situation when cruising. Car seemed to missfire and made a strange noise at about 3,000 rpms when holding speed. Then when hitting the gas, there is a noticable delay before rpms climb. Power seems to be lost too.

The car idles as if it has cams. I am not kidding. It really chugs. Sounds awesome, but not right at all. If you place you hand near the tail pipes, you can feel the air in a puff puff format. No matter which SCT tune I have my chip set at, it does this.

I suspected a bad plug or coil pack. Or something worse. But....

If I bypass the chip, the car runs smooth as hell, just the way it is suppose to. I showed two friends, the improvement is obvious.

What gives?

Could my chip have gone south on me? Or, do I have a problem with the car? Why would all the SCT tunes suddenly be like this, while the stock tune seems perfect?

Can someone help?

 

Stock tune thru SCT chip also? That would eliminate the chip as being the problem. There is the possibility of the SCT tunes being corrupted. The best answer would be to email Ryan at sctflash.com. He has helped me out a bunch!


Adam

 

Adam, when you switch to "stock tune", this tune is actually not on the chip. The chip gets bypassed and uses the tune in the ecu. I suspect the chip is the problem.

 

OK, I use an Xcal, so the chip is still "flashed" with the SCT software. Thats why I asked. Sounds like you may have a problem with the chip. They will tell you to make sure your terminals are good and clean, and then make sure the chip isn't inserted too far, the regular stuff 1st. Just kind of there protocol before assuming their product is bad. I am sure Ryan or Dev can help you out. Do you have access to the SCT users thread over at MD? If not, PM ryan on the sctflash.com board. Hope it works out for you. SCT has always been pretty quick to help me out.


Adam

 

The more I dig into this, the more I wonder if the IAC is not my problem, coupled with the fact that my SCT program may have the car idle a bit lower.

This is my current theory:

If my IAC is not functioning properly, this might explain why the car runs soo poorly on cold start. At startup, the rpms fluctuate rapidly between 400 - 800 almost as if it is struggling to get air. Ever start a car with the IAC unplugged? (I need to try this as an experiment). I believe it does the same thing.

I also noticed that the car wants to idle at about 800 rpms with the stock tune, and at about 500 rpms with the SCT tune. At the lower rpms is where I am getting the rumble-rumble after-market cam idle. I am wondering if the IAC is not opening properly and hence the problem, but the stock tune idles higher, so i don't run into this.

I am thinking to trouble shoot this, I could either replace the IAC with a new one, swap my IAC off another mustang (if I had one), or simply remove the IAC completely so the car can get all the air it wants and see what happens as it idles. I think that would essentially give the air all the air it needs at idle.

What I don't know is, what is it about the SCT tune compared to the stock tune that would allow for the lower idle? Or, could my chip still be whacked which is not allowing the car to run properly when the SCT programs are in use.

So far, I think my best theory is that the IAC is dicked.

 

Update: I think my IAC is fine, so it must be the chip.