I have no idea what's wrong with my car..
 

Hey guys, so I'm pretty new to cars and I recently bought an 05 SSL evo 8 with 82k miles, I'm not entirely sure what mods it has besides 272 cams, new gasket set and pistons (not sure what brand) GReddy BOV type Rs (which isn't blowing off.. if that makes sense) it used to have a Buschur downpipe not sure what kinda catback but they were removed because of damage to the downpipe. So open downpipe as of now, rear o2 removed. Evo 9 turbo (02 dump?) Bc coilovers. Mishimoto radiator (small one) just recently installed BPR8ES spark plugs at .026 gap. Alright so I'm having really big issues with the car, it backfires loud af whenever I try to give it gas. I have to be at around 3500rpm to get it to start rolling in 1st. Smelling a gas leak(?) behind the engine bay. Once driving it continues to backfire and has trouble picking up speed and rpm's past 2300rpm. I took it to a mechanic and I feel like he didn't do **** it's actually running worse than when I got it. He tells me I just need 02 fixed (but he removed it) new ECU and tune and a bigger turbo kit because It's holding back because of the cams and internals with the stock ecu? It had a tuned ecu before I got it but was replaced with the stock one when sold to me. Had a AEM boost solenoid but it cracked and the stock one was reconnected. Idk what to do help!!! Sorry if I messed anything up with this post but would appreciate any help!

Based on your notes, this EvO desperately needs a good EvO shop

The gas smell behind the engine is likely leaking injector seals which needs correcting ASAP

This modded 4G63 needs a tuned ECU for sure. Running on the stock ECU will damage this motor

Do your best & get an accurate listing of the mods so the tuner can match the tune to those components

Appreciate the advice, not sure there's an evo shop around my area.. but I'll get it checked out. To clarify, you're saying I can tune the stock ECU right? Opposed to what I was told about buying a new one?

The stock ECU is very tuneable. Any Evo shop or decent tuner can tell you that.

You really need to do a good boost leak test and get the car to a shop. Car needs data logged and gone over by professionals

Open down pipe is a no no. Fix that and report back.

Look up how to do a boost leak test on the Evo. Close the spark plug gap down a bit. Try to get these done asap.
If you want to enjoy the car, you really need to learn how to do a boost leak test at least. Little boost leaks can mess with driveability. Another beneficial tool will be a Tactrix cable and Evoscan. You can pick those up for cheap and learn how to datalog the car. Once you get familiar with these doing this, owning an Evo becomes way easier and more fun!
Get it running right, it will definitely be worth it!

boost leak test, maf, o2, tune...

Why would this matter?
Sounds to me like he is driving a modified Evo on a stock, untuned (or poorly tuned) ECU.

Open down pipes run like total crap.