99 nissan pathfinder starting issue

When cold engine starts on the first attemp 80% of the time, when warm its about 60-70%. Sometimes it take 2-3 attemps to start. But on the second to last attemp the engine will fire very little and then knock off.

So far I replaced the distributor, spark plugs and wires, boost sensor?, fuel pressure regulator, and checked the injector ohms and fuel pressure at the engine with the old pump. After replacing the fuel filter it started fine for a few days, after replacing the fuel pump it started fine for a week. Thus making me believe it’s a fuel issue. So I added check valves to the fuel line at the engine, both the supply and return lines. And still few days later it’s back.

...checked the...fuel pressure at the engine with the old pump.

What was it? Did you check it with the new pump?

I agree, this does indeed sound like a fuel problem. I think you’re going to need a fuel pressure test. You may have fuel leaking back into the tank, or leaking from an injector into the intake manifold. You need to know the pressure running at idle, then if it holds pressure steady after turning the engine off. Let us know what the fuel pressure test results are, then maybe we can help you on to the next step. If you’ve never done a fuel pressure test, suggest to have a shop do it, and ask if you can watch. There are certain risks involved whenever working with gasoline.