How much is it to change a fuel injector if its one or all 6 on the non turbo 1991 nissan 300zx V6 ?

Oh this is fun...

I have a 1993 300ZX N/A and have had two injectors go out on me at different times. This is an expensive fix for two reasons; 1) the injector. 2) the installation process.

If you're lucky you can find a shop or eBay seller with new or reconditioned injectors at an affordable price. $150~$275/injector is steep. Worse is the cost of removal and installation since the upper plenum and fuel rails must be removed. This is a design flaw by Nissan since you can see both screws to remove the injectors, but one is partially covered by the aliminum upper plenum (big silver colored aluminum air intake over the block). There are some sites that will talk about drilling or filing the plenum to allow access to the second screw, but this is highly frowned upon and you run the risk of putting a hole in the plenum. Best to leave this as-is.

It's cost effective to replace these yourself if you're handy with a wrench and a screwdriver. the cost for a shop to do this job is between $600 and $1000 for one injector. Most of the cost is the labor to remove and replace the plenum and fuel rails.

If you want to do this yourself, start with using a voltmeter and check each injector to find the bad one. Set the voltmeter to Ohms, disconnect the electrical from the injectors, and check the resistance between the contacts of each injector. They should read between 10 and 18 Ohms. Here's how:
http://www.2carpros.com/how_to/how_to_check_fuel_injector.htm

Here's a step by step process for replacement:
http://wiki.answers.com/Q/How_do_you_install_fuel_injectors_in_Nissan_300_ZX

Like I said, I paid for this twice and never again. Too much money for such a small part that I can do myself in my spare time.

Hope this helps!