Well I've been going part by part on my dads '85 Vette replacing things I know are bad and diagnosing new issues as they come up.

I was not getting any pressure at the fuel rail so I decided to run 12 volts to the fuel pump and it was not responding however I did hear the relay kick over when I put the key in the start position.

I replaced the fuel pump (the old one was indeed dead) but I'm still not getting any pressure at the fuel rail although I now hear the fuel pump start when I turn the key to on (it did not before I replaced it).

The fuel pressure gauge is brand new so I'm going to test it on my Mazda tonight to make sure it is working alright (I don't think it is a faulty gauge but I'd feel like an idiot if it was and I didn't test it).

I did not replace the pulsator when I had the sending unit out of the tank, could a bad pulsator be responsible for the lack of pressure?

I have replaced the fuel filter (it had the factory original). Also I have checked the fuel lines and there are no obvious signs of leakage.

I don't want to throw parts at it, but I'll admit I'm a bit of a novice at this as well. I do own a FSM though.

 

When you attached the gauge, could you tell that there was no built-up pressure in the rails? (some gas should spray out when you attach the guage)


Gary

 

Just a little seeping out, nothing actually spraying.

 

Go ahead a verify that the gauge is good. Then, since you have no pressure at the rail, start at the rear of the car and work your way forward. Disconnect the fuel output line at the tank and see if it pumps fuel during the 2 second priming period when you first turn the key to "On". If it doesn't, it could be the sock (you didn't mention it either way), the pulsator, or the hose inside of the tank. Assuming all is good, reconnect the output line and remove the return line. If you get good flow there, you know there are no blockages in the circuit and chances are the regulator is bad, not forcing pressure to be built up. If you get no return line flow, chances are there is a blockage between the pump and the Schrader valve. Disconnect and see if you have good flow at the fuel filter, and the flex hoses under the hood. Once you have the location of the blockage narrowed down, you can inspect the fuel lines for a bent, kinked, or crushed section.

RACE ON!!!

 

What is the function of the Pulsator, and is there any way to test it? How would you differentiate a problem between a Pulsator and a fuel pump?

 

The pulsator is the little device that the fuel pump plugs into on the fuel sending unit, it's this weird little chunk of rubber and metal, I don't know what it actually "does" but I do know that my fuel pump is attempting to do something because I can hear it chugging along.

 

As far as I know, a pulsator evens out pulses in the fuel system. How you get pulses from a rotating electric pump is beyond me. As near as I can see the pulsator can cause one of two problems. Either it can leak fuel, and pressure, back into the gas tank, or it can become plugged and block the fuel from flowing. I think your car will do fine without one if yours is a problem.

RACE ON!!!

 

Check the pin in the end of Gauge/hose. Mine is adjustable so you get set the right depth of pin to open the schrader valve when fully seated.

 

Did you have someone watching the fuel gauge as your primed the system?

When I first started troubleshooting the fuel system on my '85, I thought I was not getting any pressure to the rail. When I had someone else watch the gauge, I found I was getting pressure, but it would dissapear in the few seconds it took me to walk around and look at the gauge...

I ended up replacing the pulsator with a short section of fuel injection hose. I think if you try a search your see that's a common problem and fix to mysterious fuel pressure issues.

 

I did it the lonely man way, I taped the gauge to my windshield. I might try replacing the pulsator with a length of hose. I'll do more diagnostics tonight and see if fuel is even making it out of the tank.

 

I believe it is there to dampen the pulses from the injectors opening and closing, similar to what a water hammer arrestor does.

 

I would start buy checking pressure closest to the gas tank.... before the fuel filter


I know this is stupid, and i have no explanation for even posting this, but I had the same problem after I had changed the original fuel filter. I went to Autozone and purchased a new one, installed it and then this no fuel pressure, no fuel period, problem arose. I checked to make sure I installed it the right direction, which i did. Finally I got pissed off so I replaced it with another one from Autozone. Well wouldn't you know it no fuel. Finally went to GM and got an A/C Delco filter and installed it; car runs perfect. I have no way to explan what happened or why, all I know is whats the chances of me installing 2 different filters wrong 3 different times. Something was restricting both.

If I come up with something more scientific or helpful I will post....
Just wanted to share a story,

DG

 

That very well may be. That certainly makes more sense than dampening pulses from a rotory pump. My April, 1989 parts book shows one part number used from 1985 through 1990. Not used in 1984.

RACE ON!!!

 

Well I disconnected the fuel feed line to see if any fuel was coming from it when the pump attempted to prime and no fuel is leaving the tank, I'll pick up a new pulsator and pull the pump again and check to make sure the lines aren't clogged in the pump. In all honesty the pulsator probably should be replaced anyways, everything that had been sitting in that tank is in pretty sour shape.

 

I suggest ditching the pulsator and putting a hose in its place, along with clamps

 

DING DING DING
I took a pulsator apart. all it is, is two red silicone inverted cup washers at each end of a metal case that when the fuel goes in it expands the silicone rubber washers to dampen out the fuel pulses. The silicone (cups) is a sturdy compound that looks to me to be lasting, and mine are 22 years old.
If you replace it with fuel hose, you will have to roll a bead onto the metal line, and cross your fingers it doesn't pop off in a rainstorm, stranding you in the path of an oncoming flash flood, then install a worm drive clamp over the hose. The hose will have to be fuel injection style hose that is good over 50 PSI, and slid over the smooth pump outlet.
In my book, a hollow metal cannister can't impede fuel flow, so why take it out?
And remember, if General motors thought they could save pennies on a car, they can realize millions of dollars in savings with a production run of almost a million cars a year.........and they left it in.

Um, EFI-CFI I don't think they are dampening the pulses from the pump, they are limiting the line shock from eight opening and closing injectors instantly building pressure because the pump doesn't stop spinning.
You said so yourself that the pump doesn't build pressure, the line restrictions allow the pressure to build, and all the pump does in reality is provide volume.
Soooooooo......... the injectors opening and closing the restrictions shocks the fuel line, and the pulsator dampens them out.

 

why take it out - it is prone to leaks - I didnt have to roll the lines for the hose install.

I had a CSI TPI - it hammered - it is less with the hose in place of the pulsator - BTW - the RACETRONIX FP Kit I purchased from Blowerworks had the fuel line in the kit

 

Well just a quick update, I bought a replacement pulsator, had the same problem, replaced the pulsator with some fuel hose and a pair of clamps. Car starts up first try after having sat for five years... Time to have a beer.