vaccuum port on stock FPR?? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-22-2010, 02:37 PM   #1
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Default vaccuum port on stock FPR??

I take it that the device with the vaccuum port on the stock fuel rail is some sort of fuel pressure regulator. The vaccuum line goes to some sort of selonoid that's most likely controlled by the ECU.
I just installed a MegaSquirt and there is nothing controlling that Selonoid which is why I removed it and plugged the vaccuum port on the FPR.
Is that what everybody does or am I making a bad mistake here?

What's the vaccuum port on the stock FPR (if it is indeed an FPR) used for?
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Old 09-22-2010, 02:52 PM   #2
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..Dear lord.

Plug that back into the intake manifold, that port will allow fuel pressure to raise and lower with manifold pressure. No need for the solenoid though.

If you need/want any help with your MS, let me know. I'm in the area.
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Old 09-22-2010, 02:53 PM   #3
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Old 09-22-2010, 02:58 PM   #4
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LOLZ


thats all.
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Old 09-22-2010, 02:59 PM   #5
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We need pictures.

At the back of the stock fuel rail is a little black canister with one fuel hose and one vacuum line. This vacuum line should go directly to the inlet manifold, not to "some sort of selonoid that's most likely controlled by the ECU"
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Old 09-22-2010, 03:11 PM   #6
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Good question though... I'm plainly posting here to make you feel better.

I wondered the same thing, the picture of the vacuum routing on the hood shows lines going from the FPR to "some sort of selonoid that's most likely controlled by the ECU" to the intake manifold.

By seeing this thread, I will now remove the solenoid (along with any other useless solenoids around the engine bay for emissions etc...)

I want AC, powersteering and nothing else.
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Old 09-22-2010, 03:30 PM   #7
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Uhm, I think you're looking at the charcoal canister purge valve. The solenoid is mounted over by the shock tower, right?
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Old 09-22-2010, 03:34 PM   #8
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No, it's what Joe described (I removed the charcoal canister with it's selonoid and the 2 selonoides for the EGR).

How does the MS know what the current fuel pressure is if this regulator can change it according to MAP?
It can't possibly know the FP behavior of this regulator and factor it into the equation when determining injector pulse with.
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Old 09-22-2010, 03:37 PM   #9
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It doesn't need to. You simply adjust the VE fuel table which is based on load (MAP) and rpm.

you could lock the FP at 80psi and the MS could still properly maintain perfect fueling but creatively altering your fuel table
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Old 09-22-2010, 03:39 PM   #10
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Quote:
Originally Posted by guzerone View Post
How does the MS know what the current fuel pressure is if this regulator can change it according to MAP?
It can't possibly know the FP behavior of this regulator and factor it into the equation when determining injector pulse with.
EDIT:

Brain beat me to it.
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Old 09-22-2010, 03:40 PM   #11
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Makes sense, the lower FP at idle could help make it idle smoother because the injector pulses are quite short at full pressure I guess.

I'll hook it up again.
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Old 09-22-2010, 03:49 PM   #12
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I'm still trying to comprehend why anybody would have ever installed a solenoid valve inline with the vacuum reference to the FPR. I have never heard of anything like this being done by a sane person.

And yeah, the MS can deal with whatever fuel pressure you're running, so long as there is a constant relationship between fuel pressure and manifold pressure. If FP always stays the same, fine. If FP tracks MAP at a known ratio, that's fine to. But you can't have FP changing arbitrarily, as would be the case with some stupid solenoid in there.
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Old 09-22-2010, 03:53 PM   #13
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Quote:
Originally Posted by Joe Perez View Post
I'm still trying to comprehend why anybody would have ever installed a solenoid valve inline with the vacuum reference to the FPR. I have never heard of anything like this being done by a sane person.

DSMs came from the factory like that. But I guess that still fits your description of sane people
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Old 09-22-2010, 04:23 PM   #14
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All the OEM FPR does is maintain a relative difference between the target fuel pressure and the pressure it sees inside the manifold.

If you are targeting 50psi pressure, and the manifold is under vacuum of -10psi, then the actual fuel pressure will be 40psi. If you are under 14psi of boost, then the actual fuel pressure will be 64psi.
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Old 09-22-2010, 04:23 PM   #15
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Quote:
Originally Posted by Jeff_Ciesielski View Post
DSMs came from the factory like that. But I guess that still fits your description of sane people
Ok, I'm still trying to comprehend why anybody would have ever installed a solenoid valve inline with the vacuum reference to the FPR on a '90-'97 Miata.

Better?
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Old 09-22-2010, 04:39 PM   #16
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Quote:
Originally Posted by Joe Perez View Post
Ok, I'm still trying to comprehend why anybody would have ever installed a solenoid valve inline with the vacuum reference to the FPR on a '90-'97 Miata.

Better?
I was only kidding :P. Also, I meant insane people when referring to the bastards that designed those cars.
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