quick90rs

iTrader: (3)

hi, i have a 1990 camaro with a 305 that i just converted from tbi to carb. now its running an edelbrock 1404. the other day i was driving when my top radiator hose came off mustve not tightened the clamp all the way so i got out and put it back on. its sprayed antifreeze everywhere, a few minutes later i was driving when my car just sputtered and died i thought i ran out of gas so after putting more gas in the car would start but would not stay running. when i put the key in the on position the pump primed and i had fuel pressure, after starting the car the pressure would drop and an air bubble would form at the fuel inlet on the carb and the car would die. i figured this was something with the fuel pump so i spent the 60 dollars and bought and replaced one. After replacing the car does the same thing it will read pressure and when i start the vehicle the fuel pump must not be staying running and the car dies. does anyone have any idea what this could be i just installed a new filter and im running the mallory 4309 return style pressure regulator.. the problem must be electrical maybe the relay got wet with antifreeze. the main things is the pump does prime and maintains pressure but will not maintain pressure while the car is running, its like the pump does not work while the car is running. also id like to know what to do with the ALDL to test the pump, like step by step directions would be greatly appreciated. thank u all!

y84pauloflondon

Have you thought about replacing your Fuel pump relay???? (cheap)

camaronewbie

If you removed the ECM, then the pump should not prime at all! The ECM controls the priming. I guess that maybe it will prime if you left the ECM connected in the car. I'm just trying to figure out how you have the fuel pump wired since the carb swap.

I removed my ECM - thus my fuel pump would no longer prime, and my fuel pump relay was worthless (as the ECM controls it). You don't need the pump to prime with a carb, since you have plenty of fuel in the bowls of the carb to start the car. But without the ECM, the pump will still run off of the Oil Pressure Sending Unit (OPSU). There is a direct line of current from the battery to the OPSU and to the fuel pump. When the OPSU senses oil pressure, then the pump will run as long as there is pressure. Thus the fuel in the carb bowls is enough to start the car, and after the car starts the OPSU senses pressure and runs the fuel pump.

But that scenerio leads to another possible problem - the OPSU can go bad (not sensing any oil pressure) and thus the fuel pump won't run at all, or the OPSU can go bad (ALWAYS sensing oil pressure even with engine off) and this will make the pump run all the time, even with key off.

So - what I did was run the wire from the OPSU to the fuel pump relay, and out to the fuel pump. Then I wired a ground to the relay, and a hot-in-run wire. With this, the hot-in-run wire supplies current to the relay, activating it, and allowing that high voltage line from the battery (that used to go to the OPSU) to connect through the relay to the fuel pump. Now my fuel pump will run ONLY if key is on, and regardless of any oil pressure readings.

So it kind of all depends on how you have the fuel pump wired after the carb swap.

y84pauloflondon

Man, that is some nice work!!!

quick90rs

iTrader: (3)

thank you for your reply, when the pump primes it brings fuel to the carb isnt that a good thing? after I installed then carburetor i left the ecm in. it is weird because the pump primes and i get fuel in the lines and the car starts after a while the pressure drops and the car dies. My problem could be the OPSU? Is threre anyway to wire the pump the way you did and still have the priming work and is there anyway wiring it that way will not work. Your saying as soon as i turn the key on the pump will start pumping right away? where is the OPSU on my vehicle?

Also, if i put an in line fuel pump will that solve the problem or does the in tank one have to be functional?

camaronewbie

Let me explain this delicately, as there seems to be some differing opinions on the OPSU, and maybe others won't jump me if I state this properly...

There's a camp of folks that believe the ECM controls all fuel functions all the time, under all conditions, UNLESS the fuel pump relay goes bad - this camp believes that the OPSU system is simply a backup to keep the car running until you get home. Then, on the next restart, no relay, thus no priming, thus no start, which leads you to cuss, throw things, and search for the problem.

And there's me - I think that the ECM ONLY primes the pump, and nothing else. My thought is, IF the OPSU system is simply a backup system - why would GM put the inline fuse in to protect it so well, and why would the OPSU system be connected straight to the battery instead of a hot-in-run? I think the OPSU system is the default for constant running of the car - a left over design from the carb days where there was no electric pump to prime or control, and that the ECM system is an add-on to accomodate the priming needs of fuel injection.

OK - If it were me...

First, I'd check the fuse that is tucked in the fenderwell beside the battery - it's kinda hidden in there, it will just be a red wire and an orange wire, with a inline fuse pack between the two - make sure it's good - If I'm correct in my assumptions, no fuse means pump will prime via the ECM, but won't run afterwards.

If the fuse is good, then I'd disconnect the ECM and see what happens. The pump won't prime - we know that - but as I stated, there's no need for the pump to prime, as the carb has plenty enough fuel in the bowls to start the car. If the others are correct, then you've taken out the primary fuel control (the ECM) and now the pump should run off the secondary 'limp home' system, the OPSU.

If disconnecting the ECM doesn't work, then I'd leave the ECM disconnected and replace the OPSU - it's located above the oil filter, and looks like pic below - about $30. Here's a link:

http://www.autozone.com/autozone/cat...t=oil+pressure

You should have a running car by now, and should have the question answered as to whether the RCM controls fuel always or only for priming. Spi wheels and enjoy!

If you leave the ECM out, then I'd definitely rewire the OPSU wires to utilize the fuel pump relay that now is not being used at all. Why? Two problems with the OPSU system:

1) The OPSU can go bad (not sensing any oil pressure), and then you have no power to the fuel pump - if this ever happens, you can remove the connector to the OPSU, and run a paperclip between the two larger wires in the connector - your oil pressure guage won't work, but the fuel pump will run until you get home.

IF YOU EVER DO THIS - make sure to remove the fuse beside the battery when you do get home, as this paperclip trick will make the fuel pump run constantly regardless of the key until the battery is dead.

2)The OPSU can go bad (always sensing oil pressure), and then the fuel pump will run constantly as long as the battery is connected.

Hope that helps!

Oh - almost forgot - you cannot leave the in-tank pump in place and pull through it with an external pump - it will work for awhile, but eventually the external pump will fry itself trying to suck fuel through a non-working in-tank pump, and you'll be back to square one.

quick90rs

iTrader: (3)

i had power going back to the fuel pump and power at the relay so i ran a wire from a location on the fuse box that gets power only with the key in the on position to the fuel pump power wire. Now when i turn the key "on" the pump begins to run and she starts and runs like a top. I just would like to know if there is any problem with doing it this way.