Adjustable FPR, can't get below 46psi. WHY???
Drifting
Joined: May 2006
Posts: 1,428
Likes: 7
From: Chewelah Wa
I have a BBK regulator that uses a new cap, disc washer and the stock diaphram and spring. When I was putting everything together, I noticed that my bolt was too long and hitting on the plenum. I left the disc out, which allowed me to screw the bolt in farther so it would not hit the plenum. The bolt would just contact the metal cap on top of the stock spring. I thought this would work, as I did not know the purpose of the disc (and still don't). My fuel pressure was very erratic, fluctuating very rapidly up to 10 pounds at idle, making it very hard to set accurately. It would also adjust itself over time, and was very sensitive to adjustments of the bolt. My engine seemed to run fine, but this always bothered me. So I took the plenum off, installed the disc and shortened the bolt by half. Now my pressure holds steady and is less sensitive to the bolt adjustments and stays in one place. My instructions say that with the disc in, and the bolt just touching, it should be close to stock. If you need to lower the pressure, you can gasket shim the cap, cut the spring, or use a thinner disc, as mine was pretty thick. One cut out of some thin sheet metal might work. But you do need the disc in there.
Thread Starter
Instructor
Joined: Jan 2008
Posts: 150
Likes: 0
From: West Newton Pennsylvania
Le Mans Master
Joined: Oct 2008
Posts: 9,758
Likes: 49
From: Houston Texas
I have a BBK regulator that uses a new cap, disc washer and the stock diaphram and spring. When I was putting everything together, I noticed that my bolt was too long and hitting on the plenum. I left the disc out, which allowed me to screw the bolt in farther so it would not hit the plenum. The bolt would just contact the metal cap on top of the stock spring. I thought this would work, as I did not know the purpose of the disc (and still don't). My fuel pressure was very erratic, fluctuating very rapidly up to 10 pounds at idle, making it very hard to set accurately. It would also adjust itself over time, and was very sensitive to adjustments of the bolt. My engine seemed to run fine, but this always bothered me. So I took the plenum off, installed the disc and shortened the bolt by half. Now my pressure holds steady and is less sensitive to the bolt adjustments and stays in one place. My instructions say that with the disc in, and the bolt just touching, it should be close to stock. If you need to lower the pressure, you can gasket shim the cap, cut the spring, or use a thinner disc, as mine was pretty thick. One cut out of some thin sheet metal might work. But you do need the disc in there.
Last edited by ch@0s; Jul 1, 2009 at 11:54 AM.
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
I have the exactly opposite problem with a Holley Adjustable Fuel Regulator.
With a 48.5 psi pressure I changed my exhaust to a true dual free flow one. At the track With the wide band connected I noticed that the new exhaust made the Air fuel ratio too lean.
So I tried to raise the pressure. With my surprise I had no more room turning the AFPR wheel clockwise...
I continued all the day doing 1/4 miles with WOT AFR of 13.7 13.9 values..
-Beppe-
With a 48.5 psi pressure I changed my exhaust to a true dual free flow one. At the track With the wide band connected I noticed that the new exhaust made the Air fuel ratio too lean.
So I tried to raise the pressure. With my surprise I had no more room turning the AFPR wheel clockwise...
I continued all the day doing 1/4 miles with WOT AFR of 13.7 13.9 values..
-Beppe-
Le Mans Master
Joined: Oct 2008
Posts: 9,758
Likes: 49
From: Houston Texas
I have the exactly opposite problem with a Holley Adjustable Fuel Regulator.
With a 48.5 psi pressure I changed my exhaust to a true dual free flow one. At the track With the wide band connected I noticed that the new exhaust made the Air fuel ratio too lean.
So I tried to raise the pressure. With my surprise I had no more room turning the AFPR wheel clockwise...
I continued all the day doing 1/4 miles with WOT AFR of 13.7 13.9 values..
-Beppe-
With a 48.5 psi pressure I changed my exhaust to a true dual free flow one. At the track With the wide band connected I noticed that the new exhaust made the Air fuel ratio too lean.
So I tried to raise the pressure. With my surprise I had no more room turning the AFPR wheel clockwise...
I continued all the day doing 1/4 miles with WOT AFR of 13.7 13.9 values..
-Beppe-
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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The one I have is from TPI Parts, www.tpiparts.net part #FUL-200. It does not include, or call for any springs. I sent them an email to see why I can get below 46 psi. Still waiting for a reply. I will check out the one you have.
Thanks,
Thanks,
If the TPI AFPR is the SAME height as the stock bell, then it's the disk you installed that's causing the problem***. With the stock FPR, the bell/top put's pressure on the spring. (IOW, just installing a stock "bell" puts pressure on the spring. I just tried it.) And, as you should know, tightening the spring creates more pressure. By inserting the width of a disc, you compressed (tightened the spring) further. That's why your default (and minimum) pressure is higher than before.
The only way to lower your pressure will be to disassemble the unit and try again. (I doubt you'll be able to accomplish that w/o removing the plenum).
After disassembly, either toss the disc and buy a longer screw -- or purchase another AFPR that comes complete with spring/diaphram. If you choose the disc/screw method, expect the pressure to drop 2-3PSI (per the poster who suggested it). IOW, you should be back to stock pressure.
Gregg
BTW: I figured this out becaused I called TPI_Parts today and asked how the AFPR works. And, I should thank you for posting this because I might have done the same thing.
*** Footnote: This is the one question I did not ask TPIParts. However, based on your symptoms, I strongly suspect they're the same height.
Race Director
Joined: Nov 2003
Posts: 12,221
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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However, considering how the top of the spring is constructed, it's seems reasonable to assume the disc may not be necessary with this style of stock regulator.
Le Mans Master
Joined: Oct 2008
Posts: 9,758
Likes: 49
From: Houston Texas
I also like the shimming idea.You could use the ring that fits over the stock regulator.You would need to use a shorter screw or it will hit the intake and bump the pressure up. The reason I didn't do it is because I wanted to have room to work with.
Last edited by ch@0s; Jul 1, 2009 at 11:12 PM.
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Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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Le Mans Master
Joined: Oct 2008
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From: Houston Texas
I don't have one handy but as long as the bottom is flat it will work. Use the ring as a spacer between the regulator and hat. If its not flat take some sandpaper on a flat surface and make it flat.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
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Flatness (consistency of thickness) is key. Otherwise you could leak fuel. I'd put money on that ring being added just to make sure pressure is even around the ring.
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Instructor
Joined: Jan 2008
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From: West Newton Pennsylvania
I think there are some misunderstanding what I'm trying to say. If I turn the adjustment screw in, you can feel the screw is against the disc, and the more I turn it in, the higher the pressure goes. But when I back the screw out, I will get to 46 psi, (the lowest psi I can get)then the screw goes limp, and you can tell it is no longer making contact with the diaphragm. I need to get it down to at least 43 psi. I an getting 46 psi w/vac line off, and 36 psi w/vac line on. A five minute test has me smelling like exhaust, so it is without a doubt running rich.
There are some saying put a longer screw in, or shims, thats not going to do it, that will just increase the pressure...
There are some saying put a longer screw in, or shims, thats not going to do it, that will just increase the pressure...
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I think there are some misunderstanding what I'm trying to say. If I turn the adjustment screw in, you can feel the screw is against the disc, and the more I turn it in, the higher the pressure goes. But when I back the screw out, I will get to 46 psi, (the lowest psi I can get)then the screw goes limp, and you can tell it is no longer making contact with the diaphragm. I need to get it down to at least 43 psi. I an getting 46 psi w/vac line off, and 36 psi w/vac line on. A five minute test has me smelling like exhaust, so it is without a doubt running rich.
There are some saying put a longer screw in, or shims, thats not going to do it, that will just increase the pressure...
There are some saying put a longer screw in, or shims, thats not going to do it, that will just increase the pressure...
The use of a longer screw is ONLY suggested if you REMOVE the thin disk that came with your AFPR. The longer screw is suggested to reach into the depression without losing screw length above the hat.
Shims mentioned are to be placed between the top and bottom halves of the regulator. They'd raise the hat and lower the pressure against the internal spring.
Think about it until you get it.
Edit: If you still don't understand, answer one question. Did you install the thin disk with your TPI_Parts AFPR? If the answer is yes, ask yourself what would have happened if you'd put it under the original "hat" of the OEM regulator.
Last edited by GREGGPENN; Jul 2, 2009 at 12:46 PM.
Burning Brakes
Joined: Apr 2009
Posts: 1,185
Likes: 33
From: Charlotte Michigan
I have an opposite problem with only 34-35psi. Put in new pump and regulator. Also have new bosch 3's that Jon sent me as the previous owner had gotten the wrong ones for my
'93. If pressure would stay at 35 along with the volume it would be ok. I just don't like it when it spits and sputters when in dropped below 20. I also put a new filter in. I was also getting code 44 and 64 lean os2 even on the new ones I installed. Of course my goal has been fuel economy, so maybe the 35 will work.
'93. If pressure would stay at 35 along with the volume it would be ok. I just don't like it when it spits and sputters when in dropped below 20. I also put a new filter in. I was also getting code 44 and 64 lean os2 even on the new ones I installed. Of course my goal has been fuel economy, so maybe the 35 will work.
Supporting Vendor
Joined: Mar 2008
Posts: 1,762
Likes: 14
From: Cumming Ga
I think there are some misunderstanding what I'm trying to say. If I turn the adjustment screw in, you can feel the screw is against the disc, and the more I turn it in, the higher the pressure goes. But when I back the screw out, I will get to 46 psi, (the lowest psi I can get)then the screw goes limp, and you can tell it is no longer making contact with the diaphragm. I need to get it down to at least 43 psi. I an getting 46 psi w/vac line off, and 36 psi w/vac line on. A five minute test has me smelling like exhaust, so it is without a doubt running rich.
There are some saying put a longer screw in, or shims, thats not going to do it, that will just increase the pressure...
There are some saying put a longer screw in, or shims, thats not going to do it, that will just increase the pressure...
Drifting
Joined: May 2006
Posts: 1,428
Likes: 7
From: Chewelah Wa
My guess is the AFPR's are designed to work with units where a screw might fall off of -- or penetrate -- the spring assembly. More specfically, it's inserted to make insure the pressure chamber remains uniform for input/output. Non-uniform pressure on the spring could tilt the base -- creating erratic results.
However, considering how the top of the spring is constructed, it's seems reasonable to assume the disc may not be necessary with this style of stock regulator.
Shimming the installation is another good idea I didn't think of during my prior post above. Choice of shim/gasket material would obviously be of utmost importance to avoid fuel leeching.
However, considering how the top of the spring is constructed, it's seems reasonable to assume the disc may not be necessary with this style of stock regulator.
Shimming the installation is another good idea I didn't think of during my prior post above. Choice of shim/gasket material would obviously be of utmost importance to avoid fuel leeching.
