fuel pump voltage

[RAY]

Trying to diagnose if a bad pump is the reason why my fuel pressure is so low (8 psi) on my tbi conversion. I am showing 8V at the pump pigtail back by the tank and framerail when I cycle the key on and off. Is this too low? I have also tried connecting my jump starter pack to the fuel pump which is putting out 13V, but I get no change in the pressure at the throttle body with the higher voltage. This is on a stock 350 that I am converting from carb to TBI.

Thanks,
Ray

 

[1-ton]

Trying to diagnose if a bad pump is the reason why my fuel pressure is so low (8 psi) on my tbi conversion. I am showing 8V at the pump pigtail back by the tank and framerail when I cycle the key on and off. Is this too low? I have also tried connecting my jump starter pack to the fuel pump which is putting out 13V, but I get no change in the pressure at the throttle body with the higher voltage. This is on a stock 350 that I am converting from carb to TBI.

Thanks,
Ray

Actually 8-PSI is normal for a stock TBI unit. It takes an adjustable fuel pressure regulator to get any much more higher than about 9-PSI. I know there are some people that think that stock TBI units are supposed to be up around 11 or 12 PSI. The stock TBI pump may be able to go up to 11 or 12 PSI, but that is not the reality of what GM designed the fuel regulator to operate at.

 

[Bent77]

Should be 12v

 

[dyeager535]

Trying to diagnose if a bad pump is the reason why my fuel pressure is so low (8 psi) on my tbi conversion. I am showing 8V at the pump pigtail back by the tank and framerail when I cycle the key on and off. Is this too low? I have also tried connecting my jump starter pack to the fuel pump which is putting out 13V, but I get no change in the pressure at the throttle body with the higher voltage. This is on a stock 350 that I am converting from carb to TBI.

Thanks,
Ray

Should be near battery voltage. I assume you know about the prime cycle.

You can run 12V off the battery directly to the red wire dangling off the fuel pump relay connector, if that doesn't give you battery voltage at the connector further back, there is a problem with the wire. Make sure the contacts are in good shape. Dealing with similar issue with the power rear window...for some reason the connector near the firewall was randomly limiting voltage, but appears to be in good shape.

Sounds to me like your pump is no good realistically. Does it hold pressure after you prime the system? Not likely if this is a new pump/in-tank fuel hose, but if it doesn't hold pressure and they are used components, the in-tank hose may have split. Sometimes this problem is reduced if the tank is full, since the split will have some resistance to leakage with the fuel surrounding it.

 

[RAY]

I dropped the tank and inspected the plastic clamps on the fuel pump. One clamp was loose so I replaced the plastic clamps with metal clamps and now my fuel pressure is at 11psi at the TBI. Thanks for the help guys.