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more on check valve.
https://www.slantsix.org/forum/viewtopic.php?t=23054		 Page 1 of 2
Author:  Sam Powell [ Sat May 05, 2007 7:18 pm ]
Post subject:  more on check valve.
I still haven't started the slant yet, but I AM getting closer. :) I had to buy a battery charger, and get the battery charged, which is now done. I installed an electric fuel pressure gauge last week, which is mounted inside the passenger compartment. I watched the fuel pressure cycle as you turn on the ignition. The pump primes it to 43 lbs, and if you don;t fire it up, which I have not done yet, then the pump cuts off after about five seconds. At this point, the electric fuel pressure gauge shows that the fuel pressure drops almost imediately back to zero once the pump quits. This means if you THEN tried to start the car, there would be either no fuel, or certainly not enough pressure to give the injectors what they need to work correctly. Since the instructions for the EFI kit specifically call for letting the fuel pump cycle three or four times upon the initial start up, I don;t see how they expect it to ever start without a check valve. As far as the fuel rail is concerned, the car has essentially run out of fuel, and the pump will not start again until it fires, which seems unlikely with no fuel.

I dont; know why this check valve issue hasn't been discussed more in EFI circles. It now seems like a no brainer to me, and the ONLY place I have seen it mentioned is on this forum. Maybe I just missed it elsewhere. I have ordered a check valve from Summit, and it should be here on Monday. Once it is installed, I cannot see anything holding back the startup, and tuning process. I am really excited to be getting back on the road again. Thanks for all the tips, and on going discussions. They have all been more helpful thean you know. I know this has seemed like a really long, drawn out process, but there was alot to do to improve the situation,, and I didn;t see any point in trying to get it going as long as there was still a KNOWN problem to deal with. There may still be an unknown one in there, but I feel optomistic.
Sam
Author:  Pierre [ Sat May 05, 2007 9:56 pm ]
Post subject: 
Sam that seems like odd behaviour for a pump to drop to zero that quick. Next time I open my hood I'll look at the gauge and time it, but I recall my pump holding the pressure for some time after clicking off before it would start to drop.
Author:  VE Safari [ Sun May 06, 2007 2:01 am ]
Post subject: 
Quote:
Sam that seems like odd behaviour for a pump to drop to zero that quick.
I agree - that doesn't sound right.
Author:  Matt Cramer [ Sun May 06, 2007 5:01 am ]
Post subject: 
I think your fuel pressure regulator is leaking. I had similar symptoms on my Dart, and it turns out the junkyard regulator I was using had an internal leak.
Author:  Sam Powell [ Sun May 06, 2007 7:40 am ]
Post subject: 
YOu might be right. I will install the check valve, and see if it still does this. If not then it would indicate the fuel was leaking back through the pump, and not through the regulator. If it does still leak down right away, then we will know for sure it is the fuel regulator. It is a Paxton regulator, which is a respected name. Thanks for the feedback.
Sam
Author:  Charrlie_S [ Sun May 06, 2007 8:36 am ]
Post subject: 
just block off the return line from the regulator to the tank. Fire up the pump to build pressure, turn the pump off. If the pressure holds, it is the regulator. If pressure still drops, it is on the supply side (pump?).
Author:  Pierre [ Sun May 06, 2007 9:36 am ]
Post subject: 
Quote:
just block off the return line from the regulator to the tank. Fire up the pump to build pressure, turn the pump off.
Good idea - but be careful doing this the pressure will climb quite quickly.

*Runs out to car to do quick experiment* My gauge has 4 ticks between 30 and 40 psi. The inital turn on pulse of 2 second sput it at tick #3 (hmm, need to adjust fpr) and after a little over a minute it dropped one tick.

I have to be careful whenever I do anything with the plumbing. If I don't start the engine to use up any residual pressure with the pump off, even after hours of not running the engine, the latent 5-10psi of pressure sends fuel everywhere :shock:
Author:  Sam Powell [ Sun May 06, 2007 1:20 pm ]
Post subject: 
Pierre, am I to understand tht your fuel pressure holds a little over 30psi for a minute after you turn off the key? Do you have a check valve on the front side of the rail? Is your fuel rail blind at one end or through from the pump through the rail and then to the regulator, and then return?
Sam
Author:  Pierre [ Sun May 06, 2007 2:36 pm ]
Post subject: 
Quote:
Pierre, am I to understand tht your fuel pressure holds a little over 30psi for a minute after you turn off the key?
Correct. And it would of stayed like that for several minutes probably. It should be a little higher I need to adjust the regulator.

I have the stock tank pickup, to a walbro gsl392 pump strapped to frame rail by rear wheel, through the stock steel line to the injector rail, to the regulator (accufab brand universal unit) on the other side of the rail, return back to the tank. No check valves, no other voodoo.
Author:  Al T [ Tue May 08, 2007 7:24 pm ]
Post subject:  Gas Pressure
Once pressure builds in my fuel rail, it takes about 5 mins to drain from around 40 psi to 0. Bosch pump. Somethings wrong with your pump or pressure regulator Sam.
Author:  Sam Powell [ Wed May 09, 2007 4:18 am ]
Post subject: 
Is the pump suposed to function as a check valve? Do all pumps have this function? I have purchased this check valve, and only need an O ring fitting to install it between the pump and the fuel rail, so that should solve any problems with the pump in this regard. It builds pressure just fine when it is running. The pressure regulator seems to hold pressure fine as long as the pump is running, so it seems as if it is doing it's job properly; that of allowing only that fuel which is above the set pressure to pass. If it was not working properly it would seem as if it would not maintain pressure while the pump is running. Anyway, thanks for the input and for thinking about this. I will let you know what happens. I will not likely have time to install it before Friday evening.
Sam
Author:  Matt Cramer [ Wed May 09, 2007 8:00 am ]
Post subject: 
It depends on the exact design of the pump, but a gerotor-type fuel pump will act as a check valve. It would have to spin backwards to allow the fuel to flow backwards. I think most electric fuel pumps are this sort, or other sorts of positive displacement pumps.
Author:  Pierre [ Wed May 09, 2007 10:29 am ]
Post subject: 
Sam what fuel pump are you running again?

I can only guess its more likely the pump then regulator because for that big a leak, like you said, the regulator probably wouldn't be doing its job while the pump is running.

The other possibility is the fuel is leaking somewhere, either past the injectors into the intake or on the floor somewhere... :shock:
Author:  newpoppop [ Wed May 09, 2007 5:41 pm ]
Post subject: 
hey Sam, sounds like she is almost ready... maybe I can swing by next trip down that way... love to see how that all goes together... I can't get time to do anytihng to mine... still looking for headers... lol

take care, keep up the good job...

Chris
Author:  Sam Powell [ Wed May 09, 2007 7:49 pm ]
Post subject: 
Thanks in advance to anyone who takes the time to read this post, and again for those who venture opinions here. OK, most of you guys are right. The check valve, installed between the fuel rail and the pump, did NOT prevent the rapid leakdown. I had high hopes, but it looks like maybe the pressure regulator is the culprit. It builds to 40lbs and holds steady until the pump quits, and then the pressure drops off to near zero within a couple of seconds. When I crack the fuel line, there is indeed no pressure there. I cannot see any leaks that would account for that much of a drop in pressure. I can smell fuel around the gauge sending unit, but don't see anything. Nothing seems to be on the floor. I intend to get the sending unit in tighter. It goes into a 1/8th" pipe thread fitting, which I had to make, and I threaded the tap in a little too far, so the pipe thread taper opens out just a smidge too wide to snug down as tight as it needs to be. I will make another one.

If the NEW check valve is doing its job, then I can assume that the loss of pressure must be between the fuel rail inlet and the pressure regulator. I was considering taking the return line loose and emptying it into a bucket, and seeing if the pressure loss was from there after the pump quits. But it still is perplexing that the regulator holds pressure when it is pumping if it is indeed leaking there. Maybe the pump is working way more than it should be to keep the 40lbs up. If the regulator is leaking, then maybe this pump is simply strong enough to push enough fuel to keep the pressure up.

Can anyone explain how this pressure regulator works? I thought there was a spring that the fuel had to push against, and the pressure would build up until it exceeded the strength of the spring, and then let excess fuel get past the spring, thus keeping a constant threshold of PSI. It has three fuel taps. One is the return, and comes out the bottom of the aluminum body. Then there is an outlet coming out of each end of the aluminum body. One of these recieves the outlet from the fuel rail, and the other one has the pressure gauge sending unit (transponder)in it. Then there is a vacuum tap that is sourced to the TB port. Does it matter which end the fuel rail outlet is plumbed to? Is there a flow direction that matters? I assumed that this regulator was for a V-8 application with two rails, and that both ends were high pressure taps. Maybe I am wrong. If I turned the regulator around, would it still be the same?

As far as injectors leaking, I will smell the oil. I have no memory of smelling fuel in the oil in the past. Any tricks on how to determine if the injectors are leaking down? Pull the plugs maybe? It seems as if the injectors were leaking down this fast, the engine would have been running way richer than even my over rich fuel map called for, and would hae simply flooded the engine. I don;t know, maybe that was happening, except this car ran OK when it was mega squirt, and nothing has changed in the fuel rail and injector setup since then.

The fuel pump is one that someone here on the forum recomended. Maybe it was Charlie. It was from a link to a web site, and I ordered it on line. I was complaining about the original pump being way too loud at the time. Of course new parts can be deffective, and this check valve could be the culprit. I dont; know how to check it. If I could build pressure in the rail somehow, I could then open the check valve on the pump side and see if it did prevent fuel from coming back out of the rail. I am just brain storming here. I sure thinK I have honed in on something important though. Now, what to do?
Sam
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