Ive got a 2003 2l manual coupe.
On every cold start my engine makes this noise, when its fully warm it goes away. It seems to chatter after 10 ish seconds, stops and starts for the remaining time warming up and completely disappears,
Ive checked CVVT/VVT solenoid, tapits and im absolutely stumped.
Any idea what it could be?
A few days ago, someone came to me asking if I could disable the downstream O2 sensor code in his ECU, since the sensor had been removed and the car was throwing a CEL.
I do small things like this for free when I can, because it is a nice way to help people in the community. But I started getting suspicious when he told me the car was already running a “stage 1 tune” that he got from some random person in a local Tiburon group.
Usually, a lot of these so-called “tunes” are just a tiny bit of added ignition timing and nothing else. Definitely not worth the money people are charging for them. In this case, the mystery tuner could not even keep an O2-related CEL turned off for more than a few days.
Once I received the file, it became obvious almost immediately that this person had no idea what they were doing.
All of the highlighted 00s shown in the picture aren't supposed to be there. That region of the file contains configuration bits and flags, mostly related to diagnostics. So what did this guy actually turn off?
Quite a lot, unfortunately.
He disabled or heavily affected the ECU’s ability to detect issues with:
He also disabled the trigger that disengages the A/C compressor at wide-open throttle.
Because apparently, who doesn't want the A/C compressor bogging power during an overtake while also putting extra strain on the compressor pulley?
By disabling or modifying these error-detection models, he made the car less safe and less able to protect itself. If the cam sensor starts failing, you may not get a CEL and limp mode. Instead, the ECU keeps trying to run the engine without knowing there is a serious problem, which can lead to more damage.
And that was only the beginning.
Further down the file, I found that he raised the rev limiter to 7500 RPM.
Current value of RPM soft and hard limiters. Stock G4GC non-VVT limiter is at 6816 RPM.
That is a serious problem on these engines. We already start seeing valve float around 7000 RPM, and piston speeds are already very high at that point, around 22 m/s. Pushing to 7500 RPM is not “performance tuning", it's literally asking for engine failure.
Then I found more problems:
Current values (left) vs Stock values (right)
Current values (left) vs Stock values (right)
Currnet (top) vs stock (bottom)
Current values (left) vs Stock values (right)
And finally, I found changes in the program zone.
Current values (left) vs Stock values (right)
I have no idea exactly what this specific edit does, but I can say this with confidence: editing the program zone without fully understanding it is extremely dangerous.
Program zone edits are not something you casually mess with. If you change the wrong thing, you can completely ruin how the ECU controls the engine. We have spent years disassembling the program code, and we have only just managed to safely change four bytes so that larger MAF sensors can be supported.
This file had what looked like three or four lines of code wiped out. That is insane!
This is why you need to be careful who you trust with your ECU.
People like this are not tuning engines. They are disabling safety systems, hiding problems, and making the engine much more likely to destroy itself. There is no good reason to alter ECU error-detection models and diagnostic algorithms unless you are doing very specific and extreme hardware modifications, and even then, you need to know exactly what you are doing.
A random person from the internet is not always the best choice.
There are not many people who truly know how to tune these cars properly. I know most of the ones who do. There is a reason why u/chase206 and I have built a reputation in this community: everything we make is tested thoroughly. We have spent a lot of time beating on our own cars, testing, logging, learning, and making sure that what we release is safe and works properly.
I have said it before, and I will say it again:
If you are running a tune that you are unsure about, or if you get a tune from someone and want a second opinion, just send me a message. I would much rather spend a little time checking a file and making sure everything looks okay than scroll through the group the next day and see an “I blew my engine” post.
Bonus: I like how the "tuner" tried to lock the file to keep his intellectual property secure...
That isn't stopping anyone mate...
Edit: If somebody the firmware files that our ECUs run and definitions we've made for them, you can find them here. All free and open source!
