Replacing an injector

[superbikegsxr6]

I have a 91 240 SX SE, has about 142k on it, and started running rough about a month ago, but after a few minutes would run just fine. Well now its doing it all the time and idling very rough. Seems to be running on 3 cylinders, I replaced the plus, wires, fuel filter, etc, no luck. Its not the spark, so I then started pulling each plug wire from the block with the car started. The only one that didnt make the car stumble was the second one, which to me would say plugged or bad injector? Am I correct on this? Either way, whats the best way to check the injectors and walk me through replacing one. I'm good wrenching on motorcycles, havent wrenched a whole lot on cars....this car has been verrrry dependable and very low maintenance. Any guidance? I dont want to put a whole lot of money into the car, just need to get her through another winter, other than this problem she runs great!

[NISTECH]

to replace the injector. remove the 2 phillips screws holding on the cap. use a pair of long hose pliers small size put the tips in the slots on either side of the injector . twist the injector in the socket a few times then while twisting it pull up till it pops out. start with a slight pulling force then gradually increase the effort of pulling all while twisting. replace the injector and the seals. I am assuming you have already done a compression or leak down test to confirm you have enough compression in the cyl to process the burn.