Ok I will start from scratch. 1994 sidekick 4door 16v 4 weeks ago i change the block-head with a used block-head from a 1996 geo tracker 16v. I reused my intake and exhaust and replaced with new the cap, rotor, plugs, wires, water pump, timing belt. I got everthing put back in and after a few problems everthing was running great. It ran fine for 1 week then the engine died going down the road. I trailered it home and began to troubleshoot. I checked fuel pressure at the rail on the engine and had no fuel pressure 0psi so i troubleshot and found that the fuel pump was putting out fuel but not enough to register on the pressure gage. I replaced the fuel pump and pressure went up to over 80psi maxed gage out. I switched the pressure regulator with same results.The relurn line for the fuel is plugged. I dropped the fuel tank again and found that the metal tube that goes into the tank that is made into the fuel pump mounting bracket was plugged at the 90. I put 100psi of air to try and blow it out with no luck. for a temporary fix I held the return line into the fuel filler tube and turned the key now my pressure is to good at 40psi. Fuel is coming out of the return line now. When i try to start the engine it starts then dies like it is not getting fuel now??? I am getting a used fuel pump mounting bracket after work and should have it in tonight. If engine is starting and then dieing what should i check next?? It will stay running if i feather the gas but it is running rough.

Im taking a guess here but..... If you had pluggage at the tank return line your rail,regulator and injectors were all charged to 80 psi. You may have damaged 1 or more injectors. And you said you replaced the regulator after the 80 psi incident correct? If it (regulator) got to 80 psi it may be junk also. Just a thought and I hope it helps.

The regulator seems to be doing is job its holding pressure at 40psi as far as the injectors that thought crossed my mind I'm not sure how much pressure they can handle. ?? I would think they could handle it its basically a electric valve and it runs for a bit so they are opening and closing but i do not know for sure I'm no zuki expert. 

Did you check your spark plugs after running all that fuel thru your engine? Just thought I would throw it out there!

The stock injectors can handle 50+ lbs I know for a fact, but 80+, never been there. If you had junk in the fuel pump, fuel line, and several other areas of the tank, personally I would check the tank itself too. You may have enough crap in there to continually plug any new parts. Check, and clean it out if necessary. BTW, has the vehicle seen a lot of wet use, deep water, or vandals somewhere?

X2 on checking the system for debris. ck the filter by blowing backwards see what comes out or if it is very restricted. Injectors could be clogged, remove and check the inlet most have a screen loof for debris.

I replaced the fuel pump assembly and it fired right up. Fuel pressure is 40psi. I do not not what plugged the other assembly but i think it has been that way for a while.