4.3 TBI Fuel Pressure Test Questions


vtmecheng
03-26-2010, 10:58 PM
So I ran some fuel pressure tests tonight and want to find out if they are normal. This is on a '95 S10 Pickup with 4.3 TBI (Z code) and 4x4 if that matters.

1. When the key is turned to "on" the fuel lines pressurize to about 11 psi but drop back to zero once the pump stops cycling. Haynes manual says it should stay at pressure until key is turned to off but I don't know if that is true.
2. I plugged the supply line just after the filter to see if the fuel pump could maintain pressure when cycled. When the key is turned on the fuel line pressurized to about 15 psi and stayed at this pressure.
3. I plugged the return line to see if the regulator or injectors were leaking by into the throttle body. When the key is turned on the fuel line again pressurized to about 15 psi and stayed at this pressure.

So, here are my questions.
With everything connected as normal should the fuel lines maintain pressure when the key is turned to "on", pump is cycled, and remains in the on position?
If the answer to the last question is yes but the system maintains pressure when the return line is plugged then is it correct to say the regulator is bad, causing fuel to leak by into the return line under normal conditions? Thanks for the help.

jdl
03-30-2010, 11:46 AM
If you clamped the supply line, after pressure build, and pressure held steady. I thnk pressure is bleeding back through the pump. Some of the older TBI systems used to have internal pressure bleed-off, that was normal. That system, the pressure would bleed through the return line.

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