97 jimmy fuel pressure drops. hard starting

Been having a hard starting problem. Cranks too long if you don't let the pump run a few seconds first when starting. Didn't always do this. Put a guage on fuel line test port. Key on, engine off, pressure goes up to normal while pump running but quickly slides back to zero after it shuts off. Replaced pressure regulator. Still does it. I've seen mention of a "pulsator" on or near the fuel pump mentioned before as a culprit for pressure loss. Does anyone know what this is and can it be replaced by itself or does the whole fuel pump have to go? Any other suggestions for why pressure drops? Car runs ok once started.

Been having a hard starting problem. Cranks too long if you don't let the pump run a few seconds first when starting. Didn't always do this. Put a guage on fuel line test port. Key on, engine off, pressure goes up to normal while pump running but quickly slides back to zero after it shuts off. Replaced pressure regulator. Still does it. I've seen mention of a "pulsator" on or near the fuel pump mentioned before as a culprit for pressure loss. Does anyone know what this is and can it be replaced by itself or does the whole fuel pump have to go? Any other suggestions for why pressure drops? Car runs ok once started.

There should be a check valve on the fuel system that stop pressure bleed off like that.

BTW, what pressure was it reading?

at the fuel pump. The fuel pump sits down inside the sending unit and between the output line and the fuel pump is a squared pulsator, metal on one side, black plastic on the other side. These were used because the pump would build pressure, but after prolonged holding of the pressure, the fuel pump couldnt handle it and would give out, this pulsator acts as a one way valve, it stops fuel from comming backwards into the pump causing it to fail. Once the tank is out it is easily replaced.

Seeing how your going to go thought all the work of dropping the fuel tank you might as well replace the pump and screen. Vortec fuel pumps are KNOWN for their failure because its a standard 6 commutator pump that runs at double the pressure it was designed for. Do yourself a HUGE favor and dont buy an aftermarket autozone or murrays peice of junk, head to your local ACDelco supplier and get one from them. You will spend slightly more, but wont have to replace it for a long while

at the fuel pump. The fuel pump sits down inside the sending unit and between the output line and the fuel pump is a squared pulsator, metal on one side, black plastic on the other side. These were used because the pump would build pressure, but after prolonged holding of the pressure, the fuel pump couldnt handle it and would give out, this pulsator acts as a one way valve, it stops fuel from comming backwards into the pump causing it to fail. Once the tank is out it is easily replaced.

Seeing how your going to go thought all the work of dropping the fuel tank you might as well replace the pump and screen. Vortec fuel pumps are KNOWN for their failure because its a standard 6 commutator pump that runs at double the pressure it was designed for. Do yourself a HUGE favor and dont buy an aftermarket autozone or murrays peice of junk, head to your local ACDelco supplier and get one from them. You will spend slightly more, but wont have to replace it for a long while

So I have a 94 Jimmy with the tank out and I purchased one of those CHEAP (autozone) pumps ready to install. Any ideas of how to check the pump before it goes in?

Make sure that it's the right pump... Autozone has a habit of giving the wrong pumps to us....(TBI pump vs high pressure CPI)

Before you install the new pump, charge your battery up.

If the battery is low, the pump will not have enough current to keep the pressure up for starting.

Thanks for the help everyone. I was hoping to avoid dropping the tank on it, but kind of figured it was going to be in there and part of the pump itself but was hoping it might be something inline.

As I stated earlier, remove the battery and charge it completely and see if it will start.

A small reduction in current going to the pump will result in the pump not having enough power to prime the system properly.

One other thing. This may be way out there but can an inline pulsator or check valve just be installed outside of the tank without pulling the other one out?

As I stated earlier, remove the battery and charge it completely and see if it will start.

A small reduction in current going to the pump will result in the pump not having enough power to prime the system properly.


Thanks I'll give that a try before digging in too deep. Because it pressurizes up ok, and the way it droppes right to 0 when the pump shuts off, I figured something was leaking down. vs a lack of power somewhere

Make sure that it's the right pump... Autozone has a habit of giving the wrong pumps to us....(TBI pump vs high pressure CPI)


So true........ W in the VIN represents the CPI. X in the VIN represents TBI. And the CPI pumps WILL cost you more. Fixen on putting one in my truck real soon.

Z means TBI, not X