yea i had me brother in the truck turning the key on while i was down at pump with meter. this is when i got the reading of 5v from the purple wire. i got class today so i wont get to have "fun" messing around with it until tomorrow haha. i should have 12v at the wires when key is turned on right? both purple and grey?

 

No. 5v on almost all sensors and senders is correct. It's regulated to provide truest readings.
12 v on most switches or things that use power to move things.

So purple would be 5 cause it feeds the fuel gauge, {if you ground that purple, the fuel gauge should go to MAX.}

The gray 12 v because it drives the fuel pump.

 

awesome, thanks for the info. i will return with findings once i get the chance to give it a try.

 

siddhartha, How did we get from having fuel pressure to wondering if we have voltage at the pump? Did I miss something?

 

@70: i noticed that the pressure was low when i cranked with just me battery, but once i hooked up another battery (giving it a jump) the fuel pressure shot up to spec...so i was wondering if voltage had something to do with it, before i go out and spend the cash for a new pump. i haven't tested anything yet, weather out here has been bad.

 

What we are trying to say is, the pump is weak. A fuel pump has an electric motor which will build more pressure when provided with more voltage, but a pump at startup only has 12.5 or so volts to work with. Jump starting provides the other cars charging power to the party. raising voltage to around 14 volts and increasing pressure. While it's true you may have a weak connection or relay, having 45 or 50 psi now, it's very likely you have weak pump.

 

how did that pump work out for ya pontiacguy?

 

Just to make sure everything is squared away swap in a known good battery. I just had exactly the same issue with a Oldsmobile Bravada (same as the Blazer). Key on initially, 50+ fuel pressure but when I cranked the engine it fell too low to start the engine even though the engine turned over relatively well. I installed a battery which I knew was good , 12.5 volts before install and knowing it was fully charged and the fuel pressure jumped to 64 PSI and stayed over 57 PSI and the engine started right away. I will bet your battery has a weak cell. Try it and let us know.

 

You definately need to make sure the battery is good! The pump came last night. I'm in the middle of a tranny swap today, so It'll be tomorrow probably. I'll let you know.

 

New $20 pump in. Fires right up and runs well!