Switching from TBI to Carb. Edelbrock 1406. Got the expensive 3-port fuel pressure regulator, using stock in-tank pump. Installed pressure guage after regulator, before carb. Disconnected Computer. Turn key to ON, fuel pump runs, constantly. Gas coming through delivery hose to carb, but guage only reads 1psi. Carb doesn't seem to be getting enough fuel.

Shouldn't fuel pump only run for a few seconds when key turned ON but not cranking? Does this running constantly have anything to do with disconnect of computer? If so, how does one disconnect computer and maintain proper fuel pump operation?

 

you need to reconnect your computer, its tells the pump to prime when you first turn the key on, then lets it run when the engine runs. I just made the exact same swap on my 91. went from TBI to edelbrock 1406. On mine, when the engine would warm up, the pump would stop running, i had to bypass the relay and run power to an ignition source. What kind of regulator are you using? You need a return style.

 

The TBI fuel pump is run off a relay. This relay is signaled by the ECM and oil pump pressure switch. This is why the pump runs for couple seconds after key turned off, because there is still oil pressure.

Now if you haven't changed any wiring, your oil pressure switch could be toast.

 

I have the return style regulator - the $80 one from Mallory. The pump doesn't run for a "few seconds" after I turn the key off - it runs forever, as long as the battery is connected, it will run.

I don't have any sensors connected - warm or cold, there is no ECM to know, and no sensors to tell it (if it were there).

So, what is necessary for me to leave the ECM OUT, and get proper fuel pump function from the in-tank pump?

del91_305: You are saying that the relay, because it is controlled by the ECM, is causing the problem? And that I just need to connect the fuel pump to a direct hot-in-run source for proper operation? If so, can I connect the relay to a hot-in-run source, thereby maintaining the relay and wiring to the pump intact, and removing the ECM from the setup? Then I would have the safety of a relay and minimal wiring changes, right?

 

Well, it may be causing the problem, you just need to hook the ECM back up and see what it does. I swapped from TBI to carb but i left me ECM connected. And what i meant about running the pump to an ignition hot source, that was just the experience i had, in all reallity what i did was bypassed the oil pressure switch and the relay, because for some reason, it was telling the ECM that there was no oil pressure

 

Just run an ignition Hot wire to the fuel pump relay + signal. The factory relay + signal wire is usually orange/black, so verify this, then cut this wire off afew inches form the relay, and connect your new power wire.

 

Problem found! Oil pressure sending unit bad. On schematics, fuel pump gets an always hot lead through the OPSU - if OPSU is bad, sending an oil pressure signal always, then fuel pump runs always. Makes me wonder what the heck the relay is for, since fuel pump gets an always hot lead through the OPSU with or without the fuel pump relay.

This explains the battery always being dead in the car before I swapped motors - fp always running and I couldn't hear it in driveway. Lesson learned - get a quiet garage!

 

The relay is to prime the system. It also stays on as long as the ECM is getting reference pulses from the distributer. The Oil Pressure switch is purely backup should the relay fail.