Nissan Repair: fuel injectors, merkur xr4ti, nissan sentra

Question
1993 Nissan Sentra 1.6 I have no fire on #4 cylander im prety sure its an injector I only need to change the bad one right? not all four? I
once heard they dont go bad they either work or they dont is this true there very expensive  

Answer
Yes, they fail or they work.  That is, unless it is plugged up.  In your case you say you have no fire on number 4 cylinder.  I assume this means that you have spark going to the number 4 spark plug.  But, when you remove the wire there is no difference in engine performance.  So, we can say that if you have spark to the plug and you have changed the plug to verify that it is good.  The next step is to see if number 4 has compression. pull the plug and check the compression with a compresssion tester.

OK, now the easy way to see if the injector is bad and since that is what you think here is what you do.  Get a volt/ohm meter and unplug the injector harness from number 4 and another injector and check the readings.  Set the meter for 0-100 and if there is a large variance you have a bad injector.  Yes, at over $50 bucks eash they are expensive and you only have to replace one.  I like the wrecking yard.  I wonce did a Merkur XR4Ti and got all four injectors for $20 bucks at the wrecking yard.  I only needed one but had the others as spares for down the road.