I have a 1997 civic ex with a d16y5 motor swap in it. At idle the cars exhaust pops and in between 2-4k rpms the car has no power and sounds really bad. I found black soot under the bumper above the exhaust and I had both o2 sensor and thermostat sensor codes. I've replaced all 3 sensors and the codes are gone. The car still starts up everytime and doesn't sound super terrible at idle. I want to call the popping sound back fire, but it's barely there, not really loud popping like a crackle tune. I've checked tps and map sensor, both seem fine. I tried changing distributor and it didn't change anything. Car has yellow spark, not blue. I only checked cylinder 1 and 2 plugs, 1 is black around the seal and 2 is completely black. I tried taking out downstream o2 sensor to see if it ran better at all incase I had a restricted exhaust and that changed nothing either. The harness seems like it's still an ex harness I only have a 4 plug o2 sensor for both. All I can think is timing? The car still has an ex ecu from what I understand (it's p2p serial number) and I'm just completely lost... I'm going to check all my fuses and see if I can find anything. I don't understand how the guy I bought it from even had it running before this? It ran great. I thought maybe vtec was forced on all the time? The signal wire for the solenoid is kind of melted, but it always kicked in vtec like an ex at 5ish-6ish rpms when it actually worked, didn't always kick on. The timing seems correct, unless I'm supposed to use the marks on the cover instead of the top of the head for the cam gear... any help is appreciated...

 

 

No ideas?

 

Besides the obvious ? First, the P2P ECU will not run a D16Y5 correctly. The correct answer is you need to swap in a D16Y8 and move on.

 

So my y5 runs perfect in my ex with ex exu and harness. It was spark plugs and wires lol

 

spark plugs and wires made it run beautifully, I'm curious why this setup works.... but it does

 

Congratulations. An ECU designed/programmed to run a 127 HP engine will run a 115 HP engine "pretty good"... but it doesn't know that you have a lean-burn engine and it will NOT get HX fuel mileage. I think you stated the engine runs "Beautifully" because you are so excited that the engine runs at all at this point. Fouled plugs may happen again in the future since the engine will be running rich all of the time. If it starts to miss and sputter from a fouled spark plug, you know EXACTLY where to look next time.