fuel pump power fallout?

[DjTy]

here's a puzzling million dollar question me and my dad have been trying to figure out:

the fuel pump line (blue cable in our '76 monza's case) has its 12 volt when putting the switch to on but while being disconnected.

as soon as we connect it to the pump it registers 0volt and inside the dash the [TEMP/PRESS] light comes up.

even with the oil pressure sensor connected it still does the same... only way to get the fuel pump to work is to directly connect the feed to the battery.

Anyone having an idea why?

(ps. the roof light has the same problem, 12 volt, but it drops when a light is in it's place... )

[ColinOpseth]

Something shorted to ground? Could you possibly have pinched a wire when you put the motor back in?

[DjTy]

Something shorted to ground? Could you possibly have pinched a wire when you put the motor back in?

Doubt it very much as we put it in with 4 people and watching the wiring would be kept out of danger.

one thing though, the fuse for it had to be replaced under the dash...

[77 Spyder]

Is the neg battery cable bolted to the engine, & is there a ground strap, or wire going from the block back to the body?

your car might also have the ground going right from the negative terminal to the body.

When the dome light is off, but should be on (door open)
Put a test light between the negative battery post & a good body ground. If the light glows at all, or your meter shows voltage, you have a ground problem.

[marco_1978_spyder]

if the factory oil press sender is disconnected you'll need a jumper wire across the farthest terminals.

[cosvega76]

Ty,

The fuel pump gets power when the key is in the Start position, then power is routed through the oil pressure switch when in the Run position. If there is no oil pressure, or if the oil pressure switch is bad, there will be no power to the pump.

As far as your voltage problem, an open circuit will show voltage since the voltmeter draws such a miniscule amount of current. There isn't enough current available to operate the pump.

HTH

Chuck

[DjTy]

tnx for the suggestions guys, I'll check 'em out.

indeed I just connected the oilpress switch while not attached to the block. so it all be still working correct when I put everything in place.

the fuelpump works with a direct lead to the battery however so likely the ground for the pump should be ok. rooflight might need grounding checked however...


I'll let you know how it worked out.

[DjTy]

Looks like Chuck hit it right on where my problem was (again). anyway it worked fine with the oil sensor in the engine and connected like pre-swap.

[CW]

I know this is an old thread but i am having the same problem with the pump. Just wondering if the fuel pump fuse had power when you were having the problem? Mine has no power at the fuse.

[HI WINDING MONZA]

Pull the plug on the oil sensor ( should have 3 wires to it) and add a jumper to two of the terminals. Test with test light first though with key on to see which is the power wire .