Nissan Repair Questions? Ask a Mechanic for Answers ASAP
Hello my name is ***** ***** thank you for your question.
The most common cause of a No Start issue on a 91 300zx is the power transistor. If the recall was done back in the 90's it would be zip tied to the upper radiator hose. If not, it would be bolted to the front timing cover. This was the most common cause for no start issues.
The only other thing I would check is the timing belt. If that broke, the engine would not start either and you would be looking at internal engine damage.
Do you have any more questions on this?
Has the MAF sensor been checked?
That code 21 points to the power transistor which is what I originally said.
Do you have injector pulse? Where are you getting the Power Transistors you tried?
Have you checked fuel pressure? or condition of fuel by taking a fuel sample?
You want to see what kind of fuel pressure you are getting. Also make sure the fuel filter is not restricting flow.