It started when I went up in to the mountains and my mass air flow sensor went out got a new one and got a new efi relay switch but now when I go up hill it just shuts off and won't start. Any idea I got a new fuel pump and seal but I don't want to put it in yet untell I have to. Any answer will help thank you

Does it shut down when on level ground under heavy acceleration ?

No I never really tried but now it won't start at all. I got a new fuel pump today but haven't put it in.

Before you start changing parts, test for spark and test for injector pulse. These are important clues to diagnosing what has failed. If you start changing parts and the replacement part is faulty, you haven't gained any ground.

Perform tests in the link below:

https://www.askmehelpdesk.com/cars-t...ml#post2123675

I turned the key to the on position and the check engine light didn't turn on but for my 4runner I don't know where to start checking.

I don't have a fuse checker or ony thing and on some of the fuses you can't see if they are broken or not.

If your CEL is not coming on then I take it the vehicle is not starting now?
Fuses are easily checked with a circuit test light. One end grounds and the other end probes. They are readily available everywhere. So easy to use and saves from "pulling" the fuse.
The "EFI" fuse located under the hood fuse compartment, is the best place to start for no CEL coming on.