ST185 swap fuel/air ratio, Getting black smoke from my exhaust Options

[ManpreetS512]

Hey 6GC Members,

I hope you all are doing well.

My name is Manu and I am new to this site, so I apologize if this has been discussed else where and I couldn't find it. If there is already a thread, please point me to it and i'll look it over.

I have a 97 Celica GT with a JDM ST185 swap with JDM ECU. The engine is stock with no modifications thus far. This car was given to me as it sat in a garage for 10 years without ever running. Needless to say, I've gone through a lot of different issues starting with replacing fuel lines, gas tank, fuel pump, cold start injector, etc. to get the motor to crank up again.

The car did not have an exhaust since the previous owner didn't purchase one and mainly wanted to get the swap to run. When we got the motor to crank (finally), it was running really rich. So I took it to a muffler shop and had them add a catback exhaust from the downpipe back with turbo muffler and all 2.5" piping.

Now the car has black smoke coming from the exhaust when it cranks up, so I am assuming that the engine is still getting too much fuel. So friends of mine recommended that I may need a ECU tune but in order to do that I would have to purchase an expensive standalone ECU and then take it to a certified shop and have them tune it.

Before going down that route I wanted to post here to see if anyone has seen similar issues with their swap or this engine in particular? I was also wondering if anyone here knows if the O2 sensor on the downpipe is needed for the ECU to function properly? I ask because when the car was at the muffler shop, I saw the O2 sensor on the downpipe and it was not only rusted but the wire connected to it had been snipped clean - so that O2 sensor in not connected to the wiring harness at all. I also get no check engine light which is odd.

I'm thinking that the O2 sensor on the downpipe does need connection to wiring harness and someone may have snipped it to get the car running before since it had no exhaust. I am not an expert by any means and am learning as I go.

Please let me know if anyone can provide any advice.

Thanks,


Manu

[ManpreetS512]

Thank you for the quick response.

I thought of changing the downpipe to a 3" but the current one is 2.5" cast iron and the muffler shop did not want to mess with it. They ensured me that 2.5" would be good enough for my setup but I agree with your statement that 3" would've been best for proper air flow.

Hopefully that is not the limiting factor here. I'll start with connecting the O2 sensor and see what happens.

Thanks again!