ok. this will be a little long. i went from tbi to carb a year ago. loved it for a while. then got tired of tuning it with the weather changes. sold my carb set up for 450.00. then bought a harness, tbi, intake, sensors, and throttle bracket from thirdgenranch. great people. first off put on the intake and dizzy. ordered all the parts to rebuild the tbi. also ordered matched injectors from injectorwarehouse.com. also the spacer and the adjustable reg housing also. cleaned the tbi like no other. did the ultimate tbi which turned out perfection. installed all my parts and soldered all my harness back together. mounted the map in original place. ordered a no backpressure egr and mounted the egr solenoid behind the dizzy. mounted the spark module near the dizzy hidden by the harness. ordered the fittings and hoses for the tbi fuel lines. (an fittings). then ran the lines back behind the drivers side valve cover, behind the master cylinder lines and to the original steel fuel lines with adapters. installed a summit pressure gauge. started her up and set the timing at 0*. then ran it for a while at 11 psi. installed my tbi chip from harris performance and enjoyed the extra power. now the problems.
my fuel pressure would start out at 11 psi then fall to 8 psi. engine would run descent. adjusted the fuel pressure back to 11 psi. then it would fall to 8 psi again. ( when hot ) summit gauge. then began to notice when i turned the car off the fuel pump made a low growling noise. then tried to adjust it higher to 13 psi. then it dropped to 7 psi and died. turned it back down to 11 psi cold and it started. checked for leaks-- none--. car is a 1992 and a factory pump. decided to change it. read on here to go to a tpi pump.
not so bad to change pumps at all. little fanagling and it came out. looked at it and nothing seemed to be wrong. hose and all were good. filled the lines with brake clean after plugging them and found no leaks. instaled the new pump, hose, screen, and plug in harness. reinstalled the tank. started her up and got 14.5 psi when cold. she then dropped to 10 psi and held out. tried turning her up just to loose a litle pressure. she would then drop to 11 psi. no matter what i did to the adjustable reg housing i ended up at 11 psi. ok now. i ordered a new spring and installed it. now i would get 13.5 psi at start up and back to 12 psi no matter what i did. checked all harness connections. pinched off the return hose and it would go to 40 psi when i let go.--not the pump.
changed the spring and went thru 3 reg diaphrams and 2 springs. even changed relays. checked voltage at the relays and the feed wire to the pump was 12.8 volts. installed a caterpiller pressure gauge, a fuel injection pressure gauge from snap on, and a cornwell gauge. 12 psi at start up and go to 9 to 10 psi after warm. now this new pump was sounding week at turn off. and in the three seconds from the ecm prime.

now the solution. ( checked all grounds and power to the pump. grounds good. power at the relay gray wire 12.6 volts.

now the solution. after scracthing my head. i odered the racetronix fuel harness and installed it. finally a FIX!!!!!

now she is solid at a 13.5 psi. damn what a journey. at least now it is fixed. i will reccomend a racetronix harness to all.

 

That makes no sense? Glad your running though...

 

I made an, at first 12ga, (little pump) & now a 10ga/75a (big pump) circuit.

Given what high-hp MPFI builds have taught me about pump current demand it seemed prudent.

I suspect his new harness cured an existing current demand problem.

 

well if you figure that the same power harness goes from the battery then splits to the ecm, and oil pressure switch, and the relay, and then to the pump. that is a lot of 14 gauge wire. maybe a ground or 18 year old harness. now that it is a 10 gauge wire from the alternator to the pump straight it solved the problem.

 

i gotcha. Cool. Im glad you fixed it. may be a mod I do at one point and time

 

OK now that makes sense...

 

to tell you the truth i knew as soon as i turned it on for the ecm to prime. the pump was a whole new sound.

 

The OE relay, triggers the 75A relay (NAPA AR298 a Bosch knockoff), that powers my pump on 10g direct.

 

here is the harness i bought. complete plug and play.

http://www.racetronix.biz/itemdesc.a...WH-005&eq=&Tp=