I have a 92 350 and put a 96 vortec 350 in it. I kept the TBI with GMPP vortec TBI intake that I found, believe it or not, in a truck that was to be crushed the next day. Please don't hate me. Everything stock in both motors. 55lb. injectors, fuel pressure just under 13 psi. At first it ran pig rich, about 8 mi. gallon. I lowered fuel pressure through the regulator spring, now about 9 psi. Still rich, about 11 mi. gallon. My question is, Do i need to go to 40 lb. injectors? Is the 350 vortec that much more efficient that the old 350? I've looked for solutions on the web, but everyone is always making mods and has a problem opposite mine. I think that everything is hooked up correctly. It runs REALLY good in the upper RPMs. But stumbles off idle, spark plugs way too dark upon inspection. Before i fork out for injectors, i'd like to know if it can be another problem, maybe IAC? The car ran fine before the swap.

 

Is it going closed loop? What are the fuel trims?
It sounds like you've lowered your fuel pressure too much.
TBI generally likes 12 to 16 PSI of fuel pressure. Changing it shouldn't have been your first tuning option. It will just create more problems.

 

my aldl wont hook up to my computer for some reason. But will you answer one question for me? On the regulator in the TBI, when you break off the tab so the base can adjust, the base where the spring sits, does lowering the base raise the fuel pressure or lower it. I ask because I was wrong before. I did have 13 psi before, then I broke that tab off and lowered the base all of the way. I misread the guage when I said 9 lbs. The fuel pressure is actually over 15 now--my guage only reads to 15. So apparently lowering the base raised my fuel pressure??? Does the thing work opposite of waht I am thinking?

 

First step is get that datalog working. 55 lns inj's seem reasonable. and 15lbs FP is decent too. I bet you are not going CL.

 

No. Maybe you had some air bubbles or a defective gauge?

 

relaxing the spring tension reduces the FP...