1.8L Fuel Pressure Regulator Options

[Rob-O]

Changing back to FI, but a new Fuel Pressure regulator from Pelican. Installed it but didn't realize until this evening that the new regulator pressure is controlled by a bolt that is threaded through the center of the regulator, and a lock down nut holds the bolt in place. In other words, it is mechanically controlled, versus the pressure controlled regulator that I had.

Not sure if the new regulator is supposed to be that way (this part supersedes the old part) or if Pelican send me the wrong part. Just thought I'd throw the question out there tonight. Like an idiot I threw the box out so I don't know the part number of the new part. And wouldn't you know it, now that i've installed the part the part number is in an area that I can't see. No issues with pulling it out if needed. But thought the brain trust here may know off hand.

[timothy_nd28]

Most likely a Djet part. Ljets are non adjustable

[Rob-O]

Most likely a Djet part. Ljets are non adjustable

Well crap...

i'll see if I can get pics tomorrow. I ordered the correct part number on their site (Their site info matches the Bosch part number on my regulator). Maybe they just sent the wrong one...

[Rob-O]

Ugh, just checked the invoice and I somehow, even though I chose my vehicle as a 1974 Porsche 914 with 1.8L, ordered the wrong part. I'll call them tomorrow, but given that I threw the box away and the part has been mounted (but not used) I have my doubts they'll be wanting to exchange it.

[pete000]

Can some one chime in and explain why the D-Jet is mechanical and the L-Jet is vacuum? I like the idea of adjust-ability of the D-Jet unit.

[catsltd]

Can some one chime in and explain why the D-Jet is mechanical and the L-Jet is vacuum? I like the idea of adjust-ability of the D-Jet unit.

[bdstone914]

If you were sent the wrong part it can be fixed. See if you can get in there with a flash light and mirror to ID the part number marked on it.
I checked the catalog and it shows different regulators for a a 1.8L and 2.0L.
Call me at Pelican at ext 330, 888 280 7799 if you need assistance. I work from 704 Pacific coast time.

Bruce

[Rob-O]

Thanks Bruce. In this case the invoice has the 2.0L part number on it. The part looks like the 2.0L part (mechanical instead of pressure controlled). My guess is that I just ordered the wrong part somehow.

I'm sure it would be difficult to return since I don't have the box (tossed it after installing it).

[timothy_nd28]

Ljets are very sensitive to vacuum leaks, we all know this. In addition to that, Ljets are also very sensitive to incorrect fuel pressures. The fuel system is dependent on absolute manifold pressure so that the pressure drop across any injector is held constant while at any throttle position.

To maintain fuel pressure at any RPMs, I would assume the high vacuum (at idle) would cause the fuel regulator to close which would then would dump fuel (bleed off) via low pressure back to the fuel tank. As the engine rpm increases you would observe less vacuum and as the vacuum decreases proportionally this would open the fuel regulator and less bleed off fuel back to the tank. All in all, this regulator has a feedback device which helps maintain homeostasis in the system. Regulators without a vacuum line would have no idea what the engine is doing.

[timothy_nd28]

If anyone is interested, here is a picture of the inner workings. The only way to change the fuel pressure, you would need to change the spring rate.
Note the ball inside the regulator, I wonder if this serves as a check valve so that the fuel pressure is maintained when the car is off?

[Rob-O]

I'm not sure that diagram shows what we have, Tim. where did the diagram come from? Principal is most likely the same, just wonder if we really have a ball and spring check valve inside as this one does.

[timothy_nd28]

The Ljet fuel regulator should look very close to this:

That diagram picture came from this manual:

[Rob-O]

My 1.8L regulator looks exactly like that. But that picture and the diagram from the book differ quite a bit. The fuel inlet and return are on the bottom portion of the body in the diagram, with the vacuum on the top portion of the body. In the picture one of the fuel lines exits the side of the body. The diagram was probably done that way for ease of illustrating how the reg works. But I'm pretty sure the function between diagram and picture is the same.

[pete000]

My L-Jet FPR is acting a bit odd, I get 32 psi at idle. If i crack the throttle the pressure will drop to around 26psi at 3K rpm. This is under no load just checking it in the garage. I will have to relocate the gauge to test it while driving under load. If the vacuum is reduced upon opening the throttle I would think the pressure would rise?

With the Vacuum line disconnected the pressure rises to around 38 psi and will not move regardless of throttle position.

[Rob-O]

The vacuum line goes to the plenum. So if I understand The system correctly, the reg would pull vacuum when you hit the throttle. The vacuum produced would in turn pull the ball and spring and allow fuel to flow back to the tank (the regulators job). That would cause a drop in pressure in the fuel circuit because the regulator is the last item in the circuit. So if it opens, the pressure should drop. As I understand it via Clay Perrine, the FI is really only using ~28psi. That pressure is being built by the fuel pump. The regulator is there to allow excess fuel to be returned to the tank. You see 38 at idle because the fuel pump is producing this pressure, but there isn't enough vacuum being produced to open the regulator.

Ultimately the system is just trying to keep the fuel lines full. My assumption is that all five injectors would not be able to use enough fuel that it would drain the fuel lines faster than the fuel pump could replenish the line.

[timothy_nd28]

Vacuum should be at its highest at idle, and lowest at WOT. The fuel pressure should be lowest at idle (high vacuum). At idle, the vacuum pulls up the diaphram which lifts the ball, essentially short circuiting the supply and return (#6 and #7).

As you lose vacuum (higher rpm), the diaphram moves down, which pushes the ball down to be seated. This closes the bypass (less fuel going back to tank) which will raise the fuel rail pressure.

With the vacuum hose removed from the fuel regulator, you should see the highest pressure on the fuel rail. Adding vacuum to the fuel reg will decrease fuel pressure.

[pete000]

Vacuum should be at its highest at idle, and lowest at WOT. The fuel pressure should be lowest at idle (high vacuum). At idle, the vacuum pulls up the diaphram which lifts the ball, essentially short circuiting the supply and return (#6 and #7).

As you lose vacuum (higher rpm), the diaphram moves down, which pushes the ball down to be seated. This closes the bypass (less fuel going back to tank) which will raise the fuel rail pressure.

With the vacuum hose removed from the fuel regulator, you should see the highest pressure on the fuel rail. Adding vacuum to the fuel reg will decrease fuel pressure.

This is exactly as I understand the system should function.

I am just curious why mine drops when I crack open the TB which is opposite of what It should be doing...I will remote mount the gauge so I can see it while driving under load and see how it responds. Probably reads different under load conditions.

[pete000]

Follow up on fuel pressure on my 1.8 L-Jet.

I finally got around to mounting a camera to monitor my Fuel Pressure under driving conditions to verify I am getting increased fuel pressure under load.

First test:

I am seeing about 38 psi under full throttle flat ground.

And about 26 psi throttle closed decelerating.

30 psi while cruising.

(Stock L-Jet FPR with all hoses routed correctly.)

Seem about right? (IMG:style_emoticons/default/idea.gif)

[timothy_nd28]

seems correct to me

[pete000]

Video Link...

https://www.youtube.com/watch?v=dVjk0a0zk4s