Eike

Hi,

I have no fuel pressure after stopping the fuel pump. The pressure regulator is OK and the LS1 Injectors should be OK, too. The feed line is leak-proof.

What I have done:
- new fuel pump
- LS1 injectors

I know that the feed line is leak proof because I was soooooo stupid or it just was too late last week. By mistake, I interchanged the feed line and the return line at the fuel rails ... and was wondering why there was no fuel pressure. After some time running the fuel pump, I disconnected the fuel filter and there was pressure. That was the point I realized my mistake and put the lines into the right position.

Now, when the pump is running, I can adjust the fuel pressure ... but the pressure falls to zero after stopping the pump.


Could there be a damaged part because of interchanging the feed line and the return line?!?


Best wishes
Eike

hip

turn ignition switch on you will have fuel pressure

Ramanstud

there is a tech tip that will shed light on your problems. Note that just because a part is new (or recently replaced) does NOT mean it is in working order.

If you have pressure with the ignition on and the pump energized, then the pump is working.

If there are no puddles of gas in the engine compartment or running down the back of the gas tank after all this testing, then you likely don't have an external leak.

You need to pinch the return line, get fuel pressure by turning the ignition on, and see if it holds. If it does, then the problem lies with your "good" regulator.

If you pinch the return line and the pressure still drops fairly quickly, then it is likely the injectors OR the fuel damper (in-tank next to the pump) OR the pump check valve. If the pump is new, then see the former two options. If the injectors are new, then it is *likely* - but not for certain - that the pressure damper is leaking (or the connections from these components are leaking inside the tank).

Do that and tell us what you find.

viii

If you pinch the return line and the pressure still drops fairly quickly, then it is likely the injectors OR the fuel damper (in-tank next to the pump) OR the pump check valve. If the pump is new, then see the former two options. If the injectors are new, then it is *likely* - but not for certain - that the pressure damper is leaking (or the connections from these components are leaking inside the tank).


-----

great note on the dampner. bypass the dampner using the short piece of fuel hose that came with the pump and a couple of small clamps.

Eike

OK, I plugged the return line (direct at the fuel rail) ... holds pressure.
With the return line on, the pressure drops within the first minute from 50 to 20 psi ... within the next 3 minutes from 20 to 10 psi and within the next 10 minutes from 10 to zero.

The regulator makes some little noise ... like running water. I didn't notice it before, because I ever had the engine running checking the fuel pressure. Is this normal?


Best wishes
Eike

rick lambert

Pull the hose off the regulator..if you see gas....time for a new regulator.

RRT vette

My 86 FPR has a sound like the one you described. I'm thinking you have a leak in the tank. If the pressure hold at the rails and not when you release the return line it's leaking down pretty fast. (Damper/Check valve).

Eike

hmmm, the pulsation damper near the fuel pump is a part of the feed line ... that's not the problem.

Perhaps, I should hold just the pump under gas and look if it leaks at the return line ...

What's the check valve? I'm to stupid to find it in the Haynes manual.

aminnich

Wait a minute. Aren't those normal fuel bleed down numbers?

RRT vette

It looks a little fast to me. Goes from 50 psi to 20 psi in one minute. Am I reading this correctly?

Eike

correct

RRT vette

Then, from what I have read, the check valve is not holding pressure. The check valve is like the same as a toilet or kitchen sink. It stops the flow when functional and hold a presssure. In this case it is suppost to hold the returned fuel from what I know. A normal leak down of fuel pressure is much slower than stated. Usuallly when there is a leak after shutdown it is either faulty FPR, faulty injector(s), or faulty check valve. It is located on the retun line at the fuel pump.

Any other suggestions?

Mr6spd

There are really only 2 things holding the pressure in the rail when the pump is shut off. 1) the pressure regulator 2) the fuel pump's backflow resistance. There is no check valve in the return line. I personally don't think the measured leakdown rate is too excessive . . . It's probably just that the regulator does not seal real tight at zero flow. The only situation in which this would be a problem is if your engine's demand is running at the very ragged edge of your fuel pumps flow capability ... then the regulator may not maintain as high of a pressure setting as a better sealing one.