What holds fuel pressure at the rail?
- Thread starter cab233
- Start date
There is supposed to be a check valve in the pump that holds pressure once the power to the pump is turned off.
If the regulator is leaking internally, you would lose pressure when the pump was powered off. You would need a way to block the return line to test that out. With the return line blocked, the only way pressure can bleed off is through a faulty check valve in the pump.
Clamping the return line would accomplish that, but I am not certain that the line would not be damaged as a result.
Disconnecting the return line and clamping on a section of flexible rubber fuel hose that you can cap, plug or clamp would be the best way to test that theory.
If the regulator is leaking internally, you would lose pressure when the pump was powered off. You would need a way to block the return line to test that out. With the return line blocked, the only way pressure can bleed off is through a faulty check valve in the pump.
Clamping the return line would accomplish that, but I am not certain that the line would not be damaged as a result.
Disconnecting the return line and clamping on a section of flexible rubber fuel hose that you can cap, plug or clamp would be the best way to test that theory.
rd
Founding Member
Yes, there is a check valve in the fuel pump. If it fails, you will have and "extended crank" where it will take a couple of cranking efforts to get enough fuel pressure to run the engine. It will do it every time. Still runs, just a pain to start.
Checking can be done by checking the pressure with a gage, and if it falls immediatly when shut off, close the return with vice grips, check the pressure when shut down, then do the same with the feed line. If pinching the supply line holds pressure, then the pump check has failed.
Checking can be done by checking the pressure with a gage, and if it falls immediatly when shut off, close the return with vice grips, check the pressure when shut down, then do the same with the feed line. If pinching the supply line holds pressure, then the pump check has failed.
So, if i block the return line and it holds pressure, it is definitely the pump? Thanks for replying! I replied before I saw rd's response. How will the rail get pressure if you close the supply line? Also, couldnt this cause a running problem as far as not being able to adjust the pressure? If the check valve in the pump is bad is it true that the pressure wont be consistent? I never mentioned it but it is FI. Thanks for all the help your giving.
rd said:
rd's method only works if you connect a gauge to the supply side in the part of the line that is before the place where you clamp it.
I am still leery of clamping the flexible fuel lines since the ones on my stang are not just a section of rubber hose, but are an accordion type hose with a smooth rubber jacket on the outside.
Thanks for the question cab, since I recently changed my regulator. However, while the pressure dropped slowly with the stock reg, with the new Kirban, it drops right after the key is off, or right after the pump primes. So, is my Kirban shot? The car runs great otherwise, and seems to run better after the reg change.
FastGT94
Member
How slow did the pressure drop off with the stock FPR? I'm trying to trace down a lean problem and I am trying to see if there is a problem with my AFPR. Mine will gradually loose pressure over about a half an hour. My Pump is brand new but my AFPR is used. Not trying to hijack but I'm in the same boat here.
Thanks!
Thanks!
rd
Founding Member
I will admit that I only tinkered with the test sequence after I replaced the fpr on my Windstar, and it did not fix the problem. Very quickly convinced me that it was the pump. The only other reasonable item would be a leaking injector, but that should show up running rich on startup, especially if you are stopping and starting. Also, the vehicle did not light the check engine light in over a month of this problem.
I bought a gage and a Chiltons, and that is the test sequence in the book. You have to like close the supply hose just before you shut it down, with the gage installed.
Annoying, because I still have a spare, new $50 or so regulator for a 95 Windstar, and no Windstar that needs it. Ahh, the price of knowledge......
I bought a gage and a Chiltons, and that is the test sequence in the book. You have to like close the supply hose just before you shut it down, with the gage installed.
Annoying, because I still have a spare, new $50 or so regulator for a 95 Windstar, and no Windstar that needs it. Ahh, the price of knowledge......
Check valve in pump?
Black92, The pressure is supposed to stay at the rail for at least 15 minutes if not longer. I am going to pinch off my return line today and see if it holds, if it does i know my pump is bad. If your pressure drops right off after key on then you must have a slight hard start problem also. My main concern is that i am having a tuning problem because I cant adjust the pressure properly. RD says there is for sure a check valve in the pump, anyone else sure about this also?
Black92, The pressure is supposed to stay at the rail for at least 15 minutes if not longer. I am going to pinch off my return line today and see if it holds, if it does i know my pump is bad. If your pressure drops right off after key on then you must have a slight hard start problem also. My main concern is that i am having a tuning problem because I cant adjust the pressure properly. RD says there is for sure a check valve in the pump, anyone else sure about this also?
89CopCoupe
Banned
My car gets pressure as soon as I turn the key on.
It holds pressure under loads with only a slight, short drop in psi when I gas it and then it returns right back to set pressure?
As soon as I turn the key off it loses pressure
However, it fires right off every time
Both the pump and reg were replaced at the same time (about a month ago) FRPP190, BBK adjustable.
It holds pressure under loads with only a slight, short drop in psi when I gas it and then it returns right back to set pressure?
As soon as I turn the key off it loses pressure
However, it fires right off every time
Both the pump and reg were replaced at the same time (about a month ago) FRPP190, BBK adjustable.
Fuel system operation
The fuel injected system will hold pressure for a few minutes. Pressure will then bleed off, however fuel stays in the lines.
The high pressure of the FI pump and the fuel in the lines results in the instant engine startup.
A bad check valve in the fuel pump could result in an extend crank to start.
The fuel injected system will hold pressure for a few minutes. Pressure will then bleed off, however fuel stays in the lines.
The high pressure of the FI pump and the fuel in the lines results in the instant engine startup.
A bad check valve in the fuel pump could result in an extend crank to start.
It takes my car about 2 "cranks" to start. The pressure would slowly drop over a period of several hours, much longer than 15 minutes. I have a 155 pump waiting in the wings, so once I change that I will have more info. I assume, even if the FPR can't hold pressure, if the pump could, the pressure would be maintained, or vice versa. The FPR holds the pressure I set it at, and the car runs ok, so I guess I just need to get over it lol.
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