I have a 90 model 240sx with 93 ka24de engine with almost 200,000 miles. I bought the car less than a month ago and gave it basic tune up when i got it. New plugs, wires, cap and rotor. It drove great for a week or so with the tune up but a couple days later I noticed I had a cylinder that wasnt firing, after a couple tests i found that it was cylinder number four that wasnt firing. I did a compression test and all four cylinders read 140psi. I replaced the fuel pump and filter for ****s anbd giggles and it didnt help the problem so I bought a noid light and tested the injectors pulse. All the injectors were getting proper signal and pulse. So i bought an injector for cylinder number four and it still runs like crap with the new injector( cylinder number four is still dead).

Im hoping somebody has gone through the same problem and knows how to fix it cause Im not sure what the problem is now. If anybody has any ideas or suggestions I'd appreciate it.

 

if you already know that you have fuel and air the last thing left is the spark. i do now know what could cause you to miss a spark on cylinder 4 but check your connections for your ignition.

 

just out of curiosity did you remove all 4 spark plugs and hold the tb open when checking compression? 140psi i low but to be expected if the spark plugs were left in.