Fuel Check Valves
Posting Guru
Joined: Apr 2009
Posts: 2,447
Likes: 1
From: Northern Idaho
I believe they are to keep the fuel from draining back into the tank or into the fuel bowl when it is drained so you don't get air in the fuel rails.
Symptoms of failure? I don't know. Hopefully one of the real knowledgeable guys will chime and and answer that.
Symptoms of failure? I don't know. Hopefully one of the real knowledgeable guys will chime and and answer that.
Hotshot
Joined: Jan 2002
Posts: 17,988
Likes: 207
From: La La Land
If I had to guess, and I'm sure Gene could offer more solid hydraulic system theory:
Due to the injectors "filling" at different intervals and with an almost instant on and off time, a graph of the instantaneous fuel rail pressure would be all over the place instead of a nice constant value. This constant "pulsating" within the fuel rail, if allowed to get reflected all the way back to the fuel pressure regulator, might cause havoc with pressure regulation.
I believe the "check valves" only check the pressure "spikes" from getting back to the fuel filter canister, thus smoothing out the pressure to be regulated.
Remember, this is only a guess.
I have not personally dealt with them.
Pop
Due to the injectors "filling" at different intervals and with an almost instant on and off time, a graph of the instantaneous fuel rail pressure would be all over the place instead of a nice constant value. This constant "pulsating" within the fuel rail, if allowed to get reflected all the way back to the fuel pressure regulator, might cause havoc with pressure regulation.
I believe the "check valves" only check the pressure "spikes" from getting back to the fuel filter canister, thus smoothing out the pressure to be regulated.
Remember, this is only a guess.
I have not personally dealt with them.
Pop
still plays with trucks
Joined: Mar 2004
Posts: 1,743
Likes: 3
From: Twin Falls Idaho
The check valves in the heads are more of a check screen than a valve. One of the symptoms of a bad valve(plugged) is poor fuel pressure to one head or the other, low power output, rough idle. alot of us running other systems have eliminated them with adverse side affects
Barney
Barney
Cargo Master
Joined: May 2010
Posts: 3,047
Likes: 9
From: Snohomish, WA
If you think you are having a check valve issue, you can remove the fuel rail plugs in each head and install a pressure gauge to monitor the head pressure. If you shut of the truck, you can watch the gauge for the amount of bleed-down. Once you check the other side you can compare the two for differences.
The plugs are the same ones most remove to install the FRx. The one on the drivers side head is mounted back by the turbo, and the passenger head it is located right behind the AC pump, between the HPOP reservoir and the valve cover, it can be hard to see as there is a wire bundle that goes right over the top of it.
Sinister Diesel has a pretty good explanation of the check valves and their purpose.
From this site Fuel System FAQ's you can read about it, but I will paste it below.
The plugs are the same ones most remove to install the FRx. The one on the drivers side head is mounted back by the turbo, and the passenger head it is located right behind the AC pump, between the HPOP reservoir and the valve cover, it can be hard to see as there is a wire bundle that goes right over the top of it.
Sinister Diesel has a pretty good explanation of the check valves and their purpose.
From this site Fuel System FAQ's you can read about it, but I will paste it below.
Originally Posted by Sinister Diesel
Pressure, Flow, Check Valves, etc...:
The factory fuel system includes a Check Valve (CV) at the inlet of each of the cylinder head fuel rails. These CVs are not designed to prevent reverse flow of fuel at shut down. In fact, they have an orifice bored through the middle of the CV that allows the pressure in the fuel rail to be relieved. It is our belief that the CVs were designed to prevent fuel rail harmonics from disturbing the feed fuel approaching the heads (possibly to prevent foaming or other air release?). We've done some "non-scientific" testing and found that the stock fuel feed lines (poorly bent steel pieces) actually caused a bigger decrease in fuel flow (more restriction) than the CVs did. Since most of our customers want to remove the CVs with an eye on total performance gain (reduction of any restrictions in the fuel system), our kits have been built to do just that. This poses no negative effects on stock or nearly stock trucks and offers the best possible flow for those seeking to go "wild".
The factory fuel system includes a Check Valve (CV) at the inlet of each of the cylinder head fuel rails. These CVs are not designed to prevent reverse flow of fuel at shut down. In fact, they have an orifice bored through the middle of the CV that allows the pressure in the fuel rail to be relieved. It is our belief that the CVs were designed to prevent fuel rail harmonics from disturbing the feed fuel approaching the heads (possibly to prevent foaming or other air release?). We've done some "non-scientific" testing and found that the stock fuel feed lines (poorly bent steel pieces) actually caused a bigger decrease in fuel flow (more restriction) than the CVs did. Since most of our customers want to remove the CVs with an eye on total performance gain (reduction of any restrictions in the fuel system), our kits have been built to do just that. This poses no negative effects on stock or nearly stock trucks and offers the best possible flow for those seeking to go "wild".
Thread Starter
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Cargo Master
Joined: Aug 2009
Posts: 2,137
Likes: 13
From: Glendive, MT
The reason for asking is I am installing a vegistroke system. The two fuel systems are supposed to be kept seperate by check valves. With the stock check valves leaking or bleeding back, it is possible to push veg-oil back into the diesel tank through the fuel bowl and pressure regulator. Thanks for the help.
Maybe I need to take this problem to an alterative fuels forum.
Maybe I need to take this problem to an alterative fuels forum.
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