I did my own injectors recently, and while it's simple in principle, I would definitely not recommend it to anyone who is not technically/mechanically competent. It is really pretty tricky to get them right. And you most certainly need a pop tester. I've been meaning to do a write up on it but just have not had the time. But if anyone here decides to do their own, drop me a PM and I'll give you a lot of tips.
To the OP, I second checking the timing belt. If it's straight up loud and then dies, it's probably a timing issue. Old belts can loose a tooth or two and would explain your issue. Could also be your spill control valve in the head of the injection pump.