Hi newbie here so bear with me. A couple of weeks ago I put a cat-back on my 94 Ex and got a nice gain in power, last weekend I put a DC 4-1 on and actually LOST power. Somewhere in the neighborhood of 4Hp and 2 tenths in the Qm. I did have to reset the ecu because the o2 sensor was giving me trouble, but after that issue was resolved (code 43), I figured the ecu would relearn and compensate for the new airflow with more fuel.

Now, in daily driving it feels like it has more power, but it could just seem that way because it's louder. I decided to test it and sure enough, at 1/2 - 3/4 throttle it is actually faster than at WOT. The only way I can figure it is that at WOT the ecu is reverting to closed loop and a preset fuel map configured for a stock set-up and consequently not sending enough fuel to compensate for the added airflow. Does this make sense or am I way off?

Any help or suggestions would be greatly appreciated, Thanks.

 

need to add more fuel. what size of pipe is the exhaust.

 

Chip the ecu...

 

It's a 2.5" cat-back, and I thought about chipping my ecu. You guys recommend one?

 

You said it sounds really loud. Does it sound raspy at low rpms? If that's the case, you might want to check the gasket from the block to the header. You would definitely lose power that route.

 

I meant the exhaust got louder. I don't know about raspy, though. I did use a new gasket and couldn't hear any exhaust leaks. Is there a better way to check?

 

With a 4-1 header you lose some low and mid range for the top end.

I'm not sure about the 1/2-3/4 being better than wot problem.

 

Wouldn't having more top end make up fo the loss of mid-range or woul dit not be apparent in a QM run?