Hello Everyone,

I have an 89 GMC sierra 1500 with a 305 and here is my problem,


I have no fuel reaching the TBI. Here is the kicker, I hardwired the fuel pump to a switch and 12v constant, if I dont, I do not hear the pump running with the key in the ignition ready to turn her over. replaced the fuel filter, checked the lines, all is good, I can here the pump cycling when I switch(the switch not the key) it on but I only get fuel through the lines if I have the line from the tbi disconnected and near the ground it flows fine but with not much pressure, I can have the line near the tbi and suck fuel through it using my mouth(nasty I know), so i know they are ok, but even with the pump on it cant seem to push the fuel up to the height of the TBI. The return lines are ok and the truck turns over if i pour some fuel down the tbi so I know it will start up. I am figuring there is a problem with the pump itself but why would the pump still run if it wasnt dead? might there be a problem with a seal or something on the pump? Can I just put an inline pump on the fuel line instead of replacing the in tank pump?Could this be a problem with the oil pressure sending unit? How would I go about testing the oil pressure switch? if the fuel pressure isnt there to begin with would this cause the oil switch to stop working?

PLEASEEEEEE I NEED HELP!!!!

 

first things first.....you need to do a fuel pressure test and verify that you have the right pressure then you can continue to trouble shoot......does the pump come on when hooked up the right way? if not you need to look at the fuel pump relay

 

In 89 you could just replace the pump not the entire assembly and they aren't very expensive. I think the last one I bought was around $40. Sure beats the newer truck where your lucky if you can find one under $200. Remove the bed and swap that baby out. With a helper it is a couple hour job (if your bed bolts aren't rusted).

 

No the pump doesnt come on without the hardwired switch and I dont think the relay is the prob because it has power on the red output wire, now dont get me wrong it could be the issue, but from my understanding of the wiring the pump would not come on at all if the relay was toast.Correct me if I am wrong, I figure i need to do a fuel pressure test but I am almost convinced its the pump because when i disconnect the line(from the tank) at the filter I get fuel, plug the filter in, unplug the output to the tbi I get fuel(so it isnt the filter), plug the line back into the filter(checked the line no blockages) no fuel at tbi, even with it disconnected. I have to bring the tbi connect line to the ground in order to get fuel. So I am almost positive it is a pump that is clogged or lost it power. But I was under the assumption that the pump would have just died.


PLEASE LET ME KNOW WHAT YOU THINK!!!!

 

It could be the pressure regulator in the TBI assembly, but it sounds like you just don't have enough pressure = bad pump. A pressure check wouldn't hurt though.

 

I had the exact same problem on my 89 c2500, and followed the exact course of parts that you have.

The problem is on your fuel pump. There is a short piece of rubber line on the pump that connects it to the fuel line. Over time this rubber turns to bubble gum and blows a hole in the side. The pump will run but if you remove the gas cap and listen it should sound like a water fall. I checked my pressure and it was 0.5 psi. It's a real simple fix except dropping the tank to get at it.

There is a service bulletin on this but they no longer have the service kits available, it was a 2 inch piece of fuel line and 2 plastic clamps.

On the hard wired pump switch. The red wire is actually the fuel pump prime wire and should only have 12v for a short period. the power wire for the fuel pump is the gray wire. The dark green/white wire is the wire that controls the relay. When the engine is running that wire should have 12v, but there is also an oil pressure switch on that line that shuts the pump off if you lose oil pressure.