is this the fuel supply line?

[Craig 94 TA GT]

Knightfire, I've checked the vacuum line of the FPR (stock) everyday...no sign of gas at all. I'm not sure if there's a trace of the smell of gas, but it's so small that I can't really tell. But if the pressure drops from 40 to 0 in a matter of seconds, I would think that gas would be present in the vacuum line - not just a slight trace of a smell.
One test I actually did perform, that Fred mentioned in other posts, was to pressurize the system and pinch off the return line. If the pressure went up, you have a bad FPR. I did that and it ended up the pressure shot up to 80 psi. It still did significantly drop off though. (Althought I don't know how much my clamp actually sealed off the entire line). But I thought if my FPR was bad, I would be seeing the gas in the vacuum line. Is it possible for it to be bad, yet not see any gas in the vacuum line?

Tracy, I just realized what you're saying...there's no regulator to regulate the pressure if I'm gonna attach the gauge at the filter area. If my fuel pump is bad, though, and I attach the gauge at the filter area, will I still see a drop-off? I'm pretty sure it's good considering it's a new pump, however, I can never be too sure.
Thanks for your guys' help.

[Injuneer]

I don't think I said a pressure rise when the return line is blocked off means a bad fuel pressure regulator (or maybe I was incoherent when I said it ). It would be just the opposite... that proves the regulator is doing its job, and that the fuel pump is capable of 80psi.

I didn't see it in the posts above, but the usual cause of this problem is the check valve that is integral to the fuel pump. Have you ruled that out?

[Craig 94 TA GT]

Thanks for the reply Fred.
I think I read your regulator test post wrong...sorry, I'm the incoherent one

Regarding the pump, I had a brand new GM pump and sending unit installed by the mechanic. Before I took it in, I saw the fuel pressure drop from 40 to 15 psi in 2 hours. Now, it's going from 43 to 0 in seconds. The mechanic claims that as soon as he got it, he was seeing a siginificant drop off, like what I'm seeing now. He says I need new injectors and a regulator. He says he had cleaned my injectors, as well.
I strongly disagree with him, seeing that my regulator seems to be working fine, and I saw no leaks from the injectors. I also see no signs of a visible leak. Could this be causing a bad idle and some loss of power from idle to 1200 RPM? I checked the fuel pressure when it's running, and it's good at 37 psi. Vacuum line off, it jumps 6 to 7 psi. Yet it almost feels like I'm missing a cylinder until I get to 1200 RPM.
I've tried clamping the supply line, but it doesn't seem to do any good...pressure just falls no matter what. I'm thinking I can't clamp it hard enough to block off all pressure. I don't want to break the lines though!

[KnightFire]

I'd honestly replace the FPR and rule it out all together, it really does sound like a bad diaphram (if you have a flap check valve) type of regulator. You do if its OEM.

What type of data logs do you have to show it's running lean/rich? Just how bad is it? What kind of O2 readings are you getting?

It sounds like your going through what I was, but it turned out that the Aeromotive AFPRs (that I purchased) are that way by design (ball check valve), of course I had to talk to the AFPR technicians before I figured that out. I thought I purchased two bad Aeromotive AFPRs, turns out they were functioning perfectly.

I'm going to sell one (brand new in the box, tested it with a hand vacuum pump), if your interested you can get it from me and see if that cleans up your O2 readings.

Just a thought...


KnightFire

[Injuneer]

I don't think I'd try crunching down on the supply line to test things... its sort of amazing that they use that plastic at all.

Have you considered pulling the supply line off at the "connector" where it attaches to the hardline near the back of the intake, and holding a stopper over the end of the line to test how well the system holds the pressure? I sort of like golf tees as "stoppers"... not sure how that would work with the stock line/connection. I always avoided breaking those connections, prefering to remove the fuel rails with the lines still connected.

It's been so long since I even saw a stock fuel system and its components that I can't even contribute a lot of help any more...

[Craig 94 TA GT]

Knightfire, how do I go about getting the data logs from the PCM? The only readings I have is an emissions test by the mechanic after he installed the pump and cleaned the injectors.

So if I read correctly, the Aeromotive AFPR doesn't hold pressure when you turn the key on? Shoots from 45 to 0 in a matter of seconds, as soon as the pump stops charging?


That is 100% correct, but again its a different type of check valve, if your seeing this with the OEM FPR, the flapper is not closing. Do you have access to LT1 Edit or Datamaster something to that effect? I use DataMaster and my DFI setup to see whats going on with my PCM.


KnightFire

[Craig 94 TA GT]

I just found this in the Haynes manual...
"Install a fuel line shut-off adapter between the pressure regulator and the return line. With the valve open, start the engine (if possible) and slowly close the valve. If the pressure rises above 47 psi, replace the regulator. Do not allow the fuel pressure to exceed 60 psi. Also, don't attempt to restrict the return line by pinching it, as the nylon fuel line will be damaged."

I thought, if the pressure rises when you cut the return line off, the regulator is good. But the manual is stating otherwise??
I'm totally lost now.

[fastTa]

I could be completely wrong, but the way I understand this is that over time if the diaphram within the fpr weakens it cannot properly limit pressure to 41-47 psi at "no vacuum" or WOT.

Since the fuel pump is not responsible for "regulating" overall fuel pressure it is basically dumb in regards to fuel pressure so it continuously runs to maintain pressure as long as it is needed. So since the fuel pump is capable of producing a pressure of 80-90 psi or more the, fpr must limit or "regulate" the fuel pressure.

I would assume this is why gas would be found to be present in the vaccum line attached to the fpr if the fpr were to fail.

This is simply my understanding Craig. I think I would do like Knightfire said though and replace it just to rule it out.

Good luck!

[KnightFire]

Craig,
I'm sorry but I accidently hit "edit" instead of "quote" when I tried to reply to your message...


I apologize...I've done that a few times now. GGGRRRRRR
Please repost your questions and info...sometimes I guess I should pay more attention.


But there in is my response to your question.


Sorry!!!!


KnightFire

[Craig 94 TA GT]

Knightfire, don't worry about it! I will be happy to summarize what I've asked...I just want to thank you, Fred, Kevin, and Tracy for all your help. I don't recall exactly what I asked, but I think you and Fred answered my most important q's.

The only thing now is...if you haven't read my earlier posts, all of my fuel system problems started when someone vandalized my car and poured syrup in my tank. Needless to say, the insurance company hasn't looked at the car yet, so they will come by later this week, or possibly early next week. I told them it's still running bad after a new fuel pump and spark plugs. Since they do not honor any work I do to the car (not a licensed mechanic), I cannot touch anything (except for testing) until they inspect it. Since it's running bad now, I especially don't want to fix anything...then it ends up they won't think anything is wrong with the car. I am itching to change the regulator, but since I can't, all I can do is speculate what's wrong. If I can somehow rule out the regulator without changing it, then it must be the pump...something the mechanic believes is not the problem because it's new. He could have botched the installation, but I can't prove it yet.

Kevin, thanks for the good summary on the FPR. That's what I am thinking too...which is why I'm asking...
so the return line is the FPR "bleed off" line, which is the relief output of the inital 80 psi to reduce it to 40, right? If this is so, when you cut off the "bleed off" return line, and see the pressure rise, shouldn't this be normal? The pressure has nowhere to go if you cut off the line, correct? If I'm right here (not sure anymore lol), then why is the Haynes manual saying that if you cut off the return line and see an increase of pressure, then your FPR is bad. Maybe I'm misunderstanding something, but I'm still quite confused.

[Injuneer]

The fuel pressure regulator is in the return line. It is a simple "spring" that opens to allow enough recycle in the return line to drop the pressure to 43.5psi. When the pump shuts off, the spring seats the ball in the bypass channel with the same pressure that it normally uses to hold 43.5psi in the system. The diaphragm is there to allow the vacuum line to modulate the rail pressure in proportion to manifold vacuum. The 43.5psi value is the required DIFFERENTIAL pressure that the injectors are rated at. The vacuum line to the regulator is a "compensation" line that reduces the rail pressure by developing a force that helps hold the spring in the open position and reduces the spring force applied to the ball.

In effect, the pressure is held in the rail at shutoff by the spring in the FPR and the check valve on the pump.

Aftermarket "fuel management units" (FMU) used with superchargers are generally inserted in the return line after the FPR, and raise fuel pressure in response to manifold boost, by closing down the return line.... in effect, two FPR's in series, with the second one tied to the boost.

The NOS 5176 dry nitrous kit raises the fuel pressure to 85-90psi to get the extra fuel through the stock injectors, and does this by applying a pressure stream to the FPR vacuum compensation line... in effect boosting the force applied by the spring, and hence boosting the rail pressure.

Some "racing" AFPR's intentionally open the bypass to bleed off excess pressure and limit stress on the injectors in the "off" position. But these are often systems that operate at higher fuel pressures. I know my Weldon regulator allows the fuel pressure (set at 58psi) to drop as soon as the pump shuts off after 2 seconds when the key is first turned to "on".... timing the move to the "start" position get a little critical, since I have to hit that position before the pressure bleeds down too low. The aftermarket computer actually has an option to provide a pulse of all the injectors at about 75% throttle, so you can "pump" the system like a ye olde carb system. But the stock system doesn't need to work that way. Fortunately, mine starts immediately as long as the pressure hasn't bled below 20psi or so.

[Craig 94 TA GT]

Awesome explanation, as usual, Fred Thanks!
I think I understand what the Haynes manual is saying now. It's saying that the car must be running when you cut off the return line, then check if the pressure increases. Since it's running, fuel is normally being sprayed through the injectors, so if the pressure rises to over 47 psi, then the spring is opening up too much and allowing too much pressure to go back to the return line. Is this the case here? If this were happening, wouldn't I see a decrease in the pressure reading under normal circumstances (no hoses pinched/cut off)?
I've only checked this case when the system was pressurized, not when the car is running. I'm going to make a fuel line shut-off valve and place it in the return line. This way, I can check it when the car is running, and not worry about the vice grips destorying the nylon fuel line!

[Injuneer]

Not exactly how it works. Think of the pump as a (relatively) constant flow device. it pushes XXX liters per hour through the fuel system. All the fuel goes in the passenger side rail, up to the front of the rail, across the diagonal pipe, down the drivers side rail, where it sees the fuel pressure regulator. As the fuel travels through the rails, the injectors are "consuming" some of the fuel.

The regulator works by "squeezing down" on the flow coming at it from the rails, and holds the rail pressure at 43.5psi. If the injectors are using very little fuel (idle) the regulator is almost completely open, allowing most of the fuel to return to the tank. When the injectors are using a lot of fuel - peak power - the regulator closes down on the fuel coming at it, and limits the amount that returns to the fuel tank to a very small amount - just enough to keep the rails at 43.5psi (all this ignores the vacuum compensation issue, which isn't really important at this point).

If you draw a pressure profile of the fuel system, you might see the fuel tank at 0psi, the discharge of the fuel pump at 50psi, a loss of pressure because of the fuel flowing through the "pipe", 43.5psi at the rails, a loss of maybe 38psi through the constriction of the pressure regulator, and just enough pressure at the discharge of the pressure regulator to allow the fuel to flow back to the tank. If the return line loses 5psi due to friction, the pressure at the outlet of the pressure regulator will be 5psi.

The pressure profile will not vary a lot with injector flow. If the injectors take 75% of the available fuel, the regulator has to close down so that the loss of pressure is still aroung 38psi, or maybe slightly more, since it takes less pressure loss in the return line to get the smaller amount of fuel back to the tank.

The regulator (if you ignore the vacuum issues) is really a very simple device... a spring pressing a ball against a seat to restrict flow and hold the pressure high. You can see that if you pinch off the return line between the regulator and the tank, pressure will start to rise in the fuel rail. The pressure regulator will open up more to reduce the pressure in the rail. So, when you initially slightly close off the return line, the regulator should be able to open up enough to keep the pressure at 43.5psi. It is only when you close down the return line so much that no matter how far the regulator opens, it can't drop the rail pressure, because it can't open any further. At this point, the regulator is taking 0psi loss, and the "pinch" is producing the 38psi loss. Once the regulator is fully open, and you keep pinching down further on the return line, the pressure in the rails can only rise.

This is because of the "pump curve". As the flow through the system is reduced, the pressure that the pump can develop goes up. It can raise the pressure to 80 or 90 psi if you restrict the flow enough. Think of the pump curve as a straight line that runs from maybe 250 LPH at near "0" pressure, to near "0" flow at 90psi. (All of thes numbers are just examples). At 50psi is where it flows its rated capacity of 175 LH. Alter the pressure in the system, and the flow through the pump changes. The pump doesn't set the pressure, but the point at which it operates on "the curve" is determined by the flow characteristics of the piping and devices in it path.

So.... the manual is right... the pressure at the rails should not change as you START to SLOWLY close down the return line. But once you close off return flow to the point where the regulator is open as far as it can go, the pressure will start to rise, whether the regulator is healthy or not.

Long winded as usuall.....

[Craig 94 TA GT]

Now I fully understand it! I think what threw me completely off was that the manual said to close the valve slowly...but they didn't say that if you close it all the way, the pressure should rise no matter what.
Thanks Fred, you da man!

I will do the check once I am able to get some hose that will fit the hard lines to my pressure shut-off valve.

[Craig 94 TA GT]

After a few tests, I think I may have a fuel leak at the regulator, or somewhere near. When I was inspecting the car, I thought my intake oil leak was getting worse. I saw more wet black crud on the ground. However, upon further inspection, I noticed that it smelled like gas. It also evaporated...something that oil doesn't do! So I'm thinking that gas is dripping behind the intake manifold, picking up all the dirt and oil and making it look like the intake oil leak is getting worse. The regulator was a bit wet near the return line, but it's only wet when I run the car, not just pressurize the system.

I also installed a fuel shut-off adapter in the return line. The only problem is that the lines in the adapter are 1/4", not 5/16". So this is obviously a restriction. With the valve fully opened, the pressure when running was 53 psi at idle. The book says to close the valve slowly, which also restricts the system. So I'm thinking that the smaller lines has the same effect as somewhat closing the valve. And since it's over 47 psi, I'm thinking the regulator is bad.

The last test I performed was a dumb test...I hope I didn't break anything. With the return line shut-off valve fully closed, I pressurized the system. The gauge obviously shot up to 80 psi, but I quickly opened the valve to rellieve the pressure. During this time, a huge amount of gas spilled on the floor, near where the intake leak oil would be. I could not tell where it was coming from, but again, the regulator seemed a bit wet. I'm not sure if it was due to my home-made shutoff valve (that may have leaks), or something else. This is driving me insane.