hey guys i have a 1990 civic si hatch. The previous owner swapped a d15b2 motor in it (have no idea why) in replacement for the d16a6. It has a aem fuel rail, msd ignition and taylor sparkplug wires.

Ive recently been having issues with the car i am trying to address. Under load the car (only sometimes) sputters, backfires and sometimes stalls. It usually only happens when i shift into a higher gear, but also when i give it some throttle while im cruzing. I have tried replacing the fuel filter, plugs, and installed a new ground cable. I assumed that the aftermarket ignition and plug wires are fine and are not the problem. My friend thought i should try replacing the fuel pump but then realizing that the car is obviously running rich thus why it is back firing. The motor is not throwing any codes and the check engine light doesnt come on while or after the sputtering/stalling occurs. I have noticed the wiring for my o2 sensor is somewhat ghetto looking but i checked it over and it seems it should be alright. I have a parts car (1989 civic 4dr dx) and i was thinking of possibly trying the o2 sensor out of it in my hatch. Although the check engine light does not come on while it sputters and stalls, the check engine light does come on if i drive the car long distances (not while driving the car hard) but when i shut the car off and turn it back on, the light dissapears.

Any help is appreiciated, Thanks.

 

The o2 sensor is worth a try, however I don't even have an o2 sensor and my car has never done that.
Does the car smell like it's running rich?
The only other thing I can think of besides the fuel rail would be the spark plug wires.

 

Mine was having the same problem a while back, make sure that your timing is set properly and your belt is good. I set my timing and it runs worlds better. also if you're running really rich, your spark plugs could be fouled out from all the extra fuel. NGK or bosch (I forget which) makes these 4 pronged plugs that can burn all of that extra fuel out.