Just got the 383 in an ready to fire and behold the fuel pump runs when you hook up the battery! Any ideas as to what's wrong?

 

Pressure regulator?

 

Pull the vaccum hose off the pressure regulator and check for
gas.
Diaphram may be bad

Later

Irocing

 

The pump runs continuously when you hook the battery up? Does it run whether the key is on or off? Either way I would first check to make sure the fuel pump prime connector is not hooked to power. Then I would try unhooking the oil pressure switch and see if it stops. Did you prime the oil pump before you hooked up the battery? I don't think its a fuel pressure regulator problem as this has nothing to do with the fuel pump running. Hope this helps

 

When you disconnect the 2-prong oil pressure switch the fuel pump will stop. The fuel pump would run constantly when you hook up the battery.

 

Ok. So looks like you might have found the problem. Sounds like you should try replacing your oil pressure switch. What does your oil pressure gauge read with the key on engine off (should go to zero)? When you have oil pressure the switch allows power to go to the fuel pump so you either have oil pressure all the time(i don't see how) or you have a faulty switch. I guess its possible for this switch to fail in the on position but it should also read funny on your gauge. It's kind of expensive(about 70 bucks), but if it were my car I would try replacing it. Also if you do get one get it from a gm dealer.

 

I purchased a 2-prong borg-warner oil pressure switch from a local parts store for 7 bucks tonight(I've spent too much for my 383 build this year). There's two pressure switches so I hope that just this one is bad. My friend who is doing the motor swap is going to try and put it on tonight and see if that fixes it, I'll let you know, thanks!

 

Cool I hope that does it.

 

Right on the switch. But what about the relay? Couldn't that screw up and do the same malfunction? Assuming he has the duo like I duo on my 88 TBI.

 

The fuel pump relay gets signal from the ecm when you first turn the key and only turns the fuel pump on for 2 to 3 seconds. This primes the fuel system. Then once you start the car or crank the engine and build oil pressure the oil pressure switch allows power to go through it to the fuel pump. The oil pressure switch always gets power key on or off but should only allow volts to the fuel pump if it senses oil pressure. This is why I think this may be your problem. Try pulling the fuel pump relay and see what happens. Does the pump still come on?

 

What year is your car? I am looking at some wiring diagrams and will need to know.

 

1986

 

Make sure you got the right pressure switch. Any chance you bought the low-oil-pressure switch that is used to turn on the dash light when the oil pressure drops below 5psi? That would explain why it runs with the engine stopped.

Just a thought.

Lou

 

Which engine? Does your car have a real oil pressure gauge or just an idiot light? Does it zero when you turn the key forward engine not cranking?Did you pull the fuel pump relay? If so did the fuel pump quit? Which switch did you say you replaced?
If you pull the fuel pump relay and the pump continues to run then I would still say it should be your pressure switch. If you pull the fuel pump relay and it stops then we will have to check signal coming to and from the ecm.
On 89 and earlier 5.0 and 5.7 TPI's there is a lt blue wire that comes from the ecm directly to the fuel pump. If your car came with one of these engines then the above tests wouldn't work, but since when you unhooked the oil pressure switch the pump died I don't think you are getting signal from this line although it could be checked. Boy was that a run on sentence. It will make it easier when you tell me what engine the car came with.

 

ok, we replaced the oil pressure switch and that cured the consistantly running fuel pump. It runs for a couple of seconds when you turn the key but no longer runs constantly when you hook up the battery.

But, a new problem has arose. The car doesn't seem to have enough fuel or fuel pressure to actually make the engine run. I made another post on this. It has 24lb blue top injectors, holley AFPR, and a chip for 24lb injectors. We've tried adjusting the AFPR with no luck, Any ideas?

 

How did you determine that its a fuel problem? Did you hook up a fuel pressure gauge to the shrader valve? If so how much pressure?

 

My friend is doing the work. From what he told me it will have a enough pressure intially but it falls off(a lot) as doesn't hold.

 

Is your AFPR governed by vacuum? Just a shot in the dark cause no one has replyed yet. If that's the case, I would be looking what vacuum port I was hooked to and what vacuum reading it was getting. The higher the vacuum signal the less fuel pressure is needed like at idle when the vacuum is high. When you crack the throttle open and vacuum drops the PR should raise the pressure to keep up with the demand of acceration or WOT. So, if your not getting enough fuel, you might just have to much vacuum going to the regulator. OR, it might be time for one of those Walbro's!