My first time using this website so i hope im doing it right haha. So i swapped my 98 ek with a b20b high comp about a month ago. It was running perfect for about 2 weeks until i left a meet one night and issues started happening. As soon as i got off the highway the car started backfiring multiple times and struggled to get into high rpms. When i drive slowly in first the car jumps hard under 2k rpm. The exhuast is sputtering at idle and smells very rich. The new parts ive swapped is, injectors, iacv, plugs, wires, tried different ecu’s, ebay 02 sensor, tps. Engine has a skunk 2 street manifold, plm header, golden eagle fuel rail, aem fuel regulator, speed factory 70mm, aem short ram, rywire tucked harness.

 

Could be any number of things. Start ruling stuff out.

1. Check the timing.
2. Check/test the ignition system top to bottom (plugs, wires,cap, rotor, ICM, etc.).
3. Check/test fuel top to bottom (injector flow, fuel rail pressure, etc).
4. Check your compression.
5. Check for vacuum leaks.

Easier to find what's not causing it than to guess what is. Usually, you find what is causing the problem during the process. Once you know everything is working correctly, you can start checking to make sure it's the right stuff (right ECU, right injectors, etc.)

 

To add to @CX-Adam 's number 5 above:

Possibility: MAP sensor is bad, broken, has loose wires, or has a vacuum leak.

Years and years ago I had what sounds like the exact same issue after an autocross run. Backfiring, super rich exhaust and otherwise running very poorly as you described. After pouring over the engine bay it turned out that while I was on my run, the engine torqued forward and smacked the MAP sensor against the strut bar and cracked it, causing a massive vacuum leak and false MAP reading. After I swapped it for another I had laying around it ran perfectly again.