FI Volume test.

Carbs & F.I.

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Jivermo
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FI Volume test.

Post by Jivermo » Sun Jan 27, 2013 10:23 am

Can the fuel volume test ('78 FI 2L) be accurately performed from the fuel rail test nipple by 3 and 4, or is the pressure regulator exit under the bus the only place to get a proper reading?

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dtrumbo
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Re: FI Volume test.

Post by dtrumbo » Mon Jan 28, 2013 12:25 pm

Channeling Randy In Maine, yes. Every time I've read his suggestion to do the volume test it is from the 3/4 nipple.
- Dick

1970 Transporter. 2015cc, dual Weber IDF 40's
1978 Riviera Camper. Bone stock GE 2.0L F.I.
1979 Super Beetle convertible.

... as it turns out, it was the coil!

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Amskeptic
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Re: FI Volume test.

Post by Amskeptic » Mon Jan 28, 2013 4:08 pm

Jivermo wrote:Can the fuel volume test ('78 FI 2L) be accurately performed from the fuel rail test nipple by 3 and 4, or is the pressure regulator exit under the bus the only place to get a proper reading?
Any plenum ( in this case, the fuel rail between the pump output and the regulator) has equal pressure at all points. The flow at the 3/4 test nipple will be accurate. *After* the fuel pressure regulator will not necessarily be accurate, because the fuel pressure regulator is "interfering" with your reading downstream as it tries to maintain 14psi minimum (the heat soak residual pressure).
I am glad you asked this question.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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SlowLane
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Re: FI Volume test.

Post by SlowLane » Tue Jan 29, 2013 6:48 pm

Amskeptic wrote:Any plenum ( in this case, the fuel rail between the pump output and the regulator) has equal pressure at all points.
Erm, only in a static system. If there is any flow, then there must be a pressure differential. That's how flow happens.
Yes, sorry, I know: completely irrelevant to the question at hand, but I couldn't let that one pass. :geek:
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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Amskeptic
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Re: FI Volume test.

Post by Amskeptic » Tue Jan 29, 2013 10:10 pm

SlowLane wrote:
Amskeptic wrote:Any plenum ( in this case, the fuel rail between the pump output and the regulator) has equal pressure at all points.
Erm, only in a static system. If there is any flow, then there must be a pressure differential. That's how flow happens.
Yes, sorry, I know: completely irrelevant to the question at hand, but I couldn't let that one pass. :geek:
The pressure differential is maintained at the pressure regulator. Therefore the volume test must occur within the space back to the pump. A volume test *must* occur within the pump to regulator circuit. A functional regulator would reduce the volume in the test if you were to use the return hose.
Thank you for your keen irrelevant eye.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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SlowLane
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Re: FI Volume test.

Post by SlowLane » Wed Jan 30, 2013 2:18 am

Amskeptic wrote: The pressure differential is maintained at the pressure regulator. Therefore the volume test must occur within the space back to the pump. A volume test *must* occur within the pump to regulator circuit. A functional regulator would reduce the volume in the test if you were to use the return hose.
I'm not arguing with anything you say above. The point I unsuccessfully tried to make is that there must be a pressure difference between the outlet of the pump and the inlet to the regulator in order for there to be any flow at all. Granted, a picayune detail, and likely an insignificant difference (though I prefer to see some measurements before assuming that), but that's a different horse than blithely stating:
"Any plenum ( in this case, the fuel rail between the pump output and the regulator) has equal pressure at all points."
If there is equal pressure at all points, then there is nothing to drive the fluid from one point to another in the line, n'est-ce pas?
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

Jivermo
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Re: FI Volume test.

Post by Jivermo » Wed Jan 30, 2013 7:22 am

Wow-it's beginning to sound like Congress. Except for the French.

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Randy in Maine
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Re: FI Volume test.

Post by Randy in Maine » Wed Jan 30, 2013 8:23 am

So what kind of volume are you getting anyway?
79 VW Bus

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Bleyseng
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Re: FI Volume test.

Post by Bleyseng » Wed Jan 30, 2013 8:33 am

Yes, curious minds await your results. I have only tested the volume of each injector and tested the regulator setting. I figured if it sprayed all over the engine compartment there was enough volume.
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
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Reid
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Re: FI Volume test.

Post by Reid » Wed Jan 30, 2013 9:10 am

The pump has a much higher output pressure than the regulated fuel pressure. That difference and the lower intake pressure outside of the injectors is what produces flow. The pressure is the same from pump to regulator.

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Bleyseng
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Re: FI Volume test.

Post by Bleyseng » Wed Jan 30, 2013 11:41 am

Aren't these pumps rated at 80psi?
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
http://bleysengaway.blogspot.com/

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Amskeptic
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Re: FI Volume test.

Post by Amskeptic » Wed Jan 30, 2013 6:35 pm

SlowLane wrote: If there is equal pressure at all points, then there is nothing to drive the fluid from one point to another in the line, n'est-ce pas?
Yes, you are absolutely correct. And if you are open-hosing into a graduated cylinder, there will be a dramatic pressure drop AT THE HOSE, yes, and fluid shall drive.

Now for the but . . .
:bootyshake:

The great prayer for fuel injection rails is that the rail act like a plenum yes with equal pressure yes at each injector yes for as much exactitudinously equalizededation, yes? so please, consider this:

The pump-to-regulator is at a much higher pressure than any need for flow. This excess pressure is what I call the plenum effect in the rail, EVEN THOUGH yes, we have the flow of a (60 psi) pump blasting against a 36 psi regulator valve for gasoline cooling, yes. But honest to goodness, we do not have a pressure drop along the rail, this so each injector gets the same pressure drop flow rate.

What say you?

Please have fun with this sprightly conversation. Ratwell and I had a wonderful series of exchanges for years on theSamba, and the nervous nellies would startle with the Rodney King reflexive anxiety on us, then Mr. Breeze would shut it down..
Colin
(I haven't even hit the caps LOCK YET)
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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SlowLane
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Re: FI Volume test.

Post by SlowLane » Wed Jan 30, 2013 11:27 pm

Amskeptic wrote:The great prayer for fuel injection rails is that the rail act like a plenum yes with equal pressure yes at each injector yes for as much exactitudinously equalizededation, yes?
No argument. That would be the holy grail.
Amskeptic wrote:The pump-to-regulator is at a much higher pressure than any need for flow. This excess pressure is what I call the plenum effect in the rail, EVEN THOUGH yes, we have the flow of a (60 psi) pump blasting against a 36 psi regulator valve for gasoline cooling, yes.
My take on it is that the "excess" plenum pressure is the pressure that was engineeered into the system to provide adequate fuel atomization by the injectors.
The pump, although capable of producing much higher pressure than the regulated ~36 psi across the injectors, will not do so, unless there is an unreasonable obstruction between the pump and regulator. In short, the pump will provide precisely enough pressure to overcome the regulator's resistance plus the line losses. Which brings us to the next question:
Amskeptic wrote:But honest to goodness, we do not have a pressure drop along the rail, this so each injector gets the same pressure drop flow rate.
I beg to differ, sir. Fluid flows from a high pressure location to lower pressure locations. The fact that fuel flows from the pump outlet to the regulator inlet implies that there is a pressure drop along the rail. The questions are: how much of a drop, and is it significant enough to affect mixture control? I hope to replumb my fuel loop at same point so that I can actually measure the pressure difference between the 1-2 side and the 3-4 side and thereby be able to provide a more cogent answer.

This may seem needlessly nit-picky, but consider this: VW implemented a split dual-ring fuel rail for the wasserboxers. The fuel feed splits into two going into the engine compartment wth a branch going to each side of the engine, then meeting back in the middle into a fancy two-port FPR. If the single-loop system on the aircooled engines was adequate, why did they go to the expense of re-designing it into a dual-ring system?

Looking closer to modern times, more recent FI systems use a "dead-head" fuel pressure system, where the fuel rail itself isn't part of the high-volume loop, but rather acts as a largely static high pressure reservoir for the injectors. All this goes in concert with the more precise and accurate control of fuel injection timing and duration that these more modern systems can attain.
(I haven't even hit the caps LOCK YET)
And I pray you continue to resist the temptation. Shouting rarely helps in intelligent discourse.
:alien: Goofy smilies, on the other hand, are obligatory... :sunny:
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

Reid
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Re: FI Volume test.

Post by Reid » Thu Jan 31, 2013 6:12 am

Modern fuel systems that are non-return are a product of the goal of reduced evaporative emissions. The fuel doesn't cool the rail, so it's not returning heat to the tank. The pumps typically are not run at 100%, but are pulse width modulated by the processor with feedback from a fuel rail pressure sensor.

Reid
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Re: FI Volume test.

Post by Reid » Thu Jan 31, 2013 6:29 am

Maybe a water cooled Vanagon had bank fired injectors instead of our batch fired injectors? The engineers could have been trying to minimize a pulse on the other bank, I guess.

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