IHADAV8.com - Turbo Buick Tech, and Nonsense
Tech Area => General Buick Tech => Topic started by: Joel Russo on November 13 2013, 12:52:20 PM
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So I dug out an extra Auto Meter liquid filled Pro Comp fuel pressure gauge out of the extra race car crap, and decided to mount it on the hood to monitor the pressure under boost. I mocked up a plate, used some Pro Flo hose and Earl's fittings and made sure it didn't leak. I have a small gauge on the rail that I have been using for years to set the pressure....Ap pears as though I have a discrepency between the two.
The rail mounted gauge reads 46 psi with the vac line off of the Accufab regulator.
At idle with the vac line on and me sitting in the car, the hood mounted gauge reads 52 lbs. I ran the car a bit to make sure my pressure raises 1:1 under boost, and it does. At 10 psi boost, pressure is 62 lbs. Scanmaster tells me I'm at 780-800..
So, What gives?? :chin:
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I took a look at the inside of an accufab regulator and I'd be amazed if any of them work correctly.
It's odd you're running more pressure than you should though. I guess it's better than losing pressure under boost.
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I took a look at the inside of an accufab regulator and I'd be amazed if any of them work correctly.
You're the second person in two days that told me that about the Accufab...
So what regulator is the one to use?
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the rail mounted gauges are usually a p.o.s. when new and go down hill from there. On the other hand, I would not be surprised to find the other gauge might be bad. With gauges, quality is often reflected in the price. 52 does not sound right because with the hose on, engine running the pressure should be in the 30's.
Accufab is as good as any other as far as I have seen
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43-44 psi is where most (I think all) chips see static fuel pressure (idle rpm vacuum bias) around 700 rpm. 46 psi is static fuel pressure adjustment error (+2 psi) maybe. Your short term integrator should be driving learns closer to 128. With the static fuel pressure set to 44, pull the vacuum line off the regulator and your fuel pressure should be 38-39 psi. I wonder if you have a tear in the regulator diaphram or the spring is snagged/stuck. I wonder if a messed up return line could cause this?? 52 psi with the line off is not correct. The old KENNE BELL regulators seemed to work well and are meant to be rebuilt as necessary. If I sound like a nut case it's cause I am. Long day at work.
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43-44 psi is where most (I think all) chips see static fuel pressure (idle rpm vacuum bias) around 700 rpm. 46 psi is static fuel pressure adjustment error (+2 psi) maybe. Your short term integrator should be driving learns closer to 128. With the static fuel pressure set to 44, pull the vacuum line off the regulator and your fuel pressure should be 38-39 psi. I wonder if you have a tear in the regulator diaphram or the spring is snagged/stuck. I wonder if a messed up return line could cause this?? 52 psi with the line off is not correct. The old KENNE BELL regulators seemed to work well and are meant to be rebuilt as necessary. If I sound like a nut case it's cause I am. Long day at work.
Had some time yesterday so I ran the car a bit.
Rail mounted gauge reads 46 psi with vac line off, and only drops to 45 with the vac line on.
Hood mounted gauge reads 52.5 psi with vac line off, and only drops to 52 with the vac line on.
My scanmaster mil vols read 780-800 under boost in third gear.
I have an old Kenne Bell fpr that was working fine when I took it off. Should I buy a new Pro Comp fuel gauge for the hood and see what it reads, or replace the Accufab with the Kenne Bell and see what gives. I'm thinking I'm in the correct range according to the scanmaster numbers, and probably have a bad gauge or two...
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how much vacuum is the car making when idling?
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how much vacuum is the car making when idling?
I don't have a vacuums gauge, so how would I measure it?
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with a boost gauge that has vacuum on it, or a vacuum gauge. Vacuum is one of the most useful readings you can look at to determine if the engien is okay, or there is something wrong with it.
If another gauge does not read properly, i would take the regulator apart and see if the diaphragm has a hole in it or something else wrong
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My boost gauge does not read vacuum. I ordered a new Pro Comp liquid filled fp gauge today, so I'll swap it in and see what pressure it reads. If it still reads high, I'll take the Accufab apart and inspect.
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When you set the fuel pressure with the hose OFF the regulator, it should normally read 43 psi for a TT chip.
When you put the hose back ON with the engine running, the vacuum normally in the hose will reduce the fuel pressure to something like 36 psi because the vacuum sucks up on the diaphragm and bypasses more fuel.
When the vacuum is reduced under throttle to zero while accelerating (just before boost registers), the fuel pressure should again be 43.
When the boost rises to say 10 psi, then the fuel pressure should read 53 psi as the diaphragm is being pushed down and less fuel is by passed.
How the fuel pressure can possible rise above the base setting when you install the hose at idle is beyond me because the vacuum in the hose should be dropping the pressure that the gauge sees.
First thing I would do is stick my thumb over the end of the hose and see if it is sucking against my thumb like it should be. Second thing I would do is go by a cheap vacuum gauge at the store and stick it in the end of the hose to see exactly how much vacuum the car is making at idle to see if there is another problem with the car. third thing I would do is to take the regulator apart and see if the diaphragm is holed or cannot move for some reason...but I already said that
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My boost gauge does not read vacuum. I ordered a new Pro Comp liquid filled fp gauge today, so I'll swap it in and see what pressure it reads. If it still reads high, I'll take the Accufab apart and inspect.
It's good to read vacuum, because it will tell you if you hurt something. I usually pull 18" of vacuum, when I blew my head gasket I pulled 0". :rofl:
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43-44 psi is where most (I think all) chips see static fuel pressure (idle rpm vacuum bias) around 700 rpm. 46 psi is static fuel pressure adjustment error (+2 psi) maybe. Your short term integrator should be driving learns closer to 128. With the static fuel pressure set to 44, pull the vacuum line off the regulator and your fuel pressure should be 38-39 psi. I wonder if you have a tear in the regulator diaphram or the spring is snagged/stuck. I wonder if a messed up return line could cause this?? 52 psi with the line off is not correct. The old KENNE BELL regulators seemed to work well and are meant to be rebuilt as necessary. If I sound like a nut case it's cause I am. Long day at work.
this is incorrect
static (or base FP) is the pressure with line off or as it would read at 0psi reference
line off should be 44 (varies with chip to achieve a blm around 128 ) and upon hooking back the vaccum line the pressure should drop
the amount of drop should be roughly 1/2 of the reading you would see on a vacuum gauge because vacuum gauges read in In/HG and the conversion to psi is roughly 1/2
so if you have 18in/hg of vac on your gauge the pressure should drop 9psi (if satic was 44 new pressure should be 35) but dont expect that to happen on a stock return line with a hotwired 255lph pump
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If all is well and you remove the vacuum bias line from the regulator and the static fuel pressure should be 44.1 psi (with a 3 bar regulator). When I previously stated "static fuel pressure" I have regarded that to mean no vacuum/boost pressure influence on the regulator.Sorr y about the confusion.
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A bit of a follow up on this issue.
I bought a new Fuel pressure gauge for the hood mount, and it reads 42 psi with the vac line off the fp regulator. Looks like the old gauge was not accurate... I also bought a vacuume gauge to see if I had poor vacuume. I pulled the hose off the regulator and read 19" of vacuume.
When I put the hose back on the regulator, the fuel pressure only drops 1/2 to 1 psi.
PacecarTA said " so if you have 18in/hg of vac on your gauge the pressure should drop 9psi (if satic was 44 new pressure should be 35) but dont expect that to happen on a stock return line with a hotwired 255lph pump "
I have a Walbro 255, Hotwire kit, and stock return line... Am I good, or should I swap in a different regulator?
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connect your vacuum gauge to the line going to the regulator and see what you read there. If you read 19 in/hg at that point, It would seem the regulator is bad.
I take it that you saw nothing wrong when you took the regulator apart?
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Steve~ I read vacuume on the line going to the regulator. I did not take the Accufab apart yet, I'll do it tomorrow. What am I looking for in terms of a "bad regulator"?
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tear or cut in the diaphragm or it is stuck so it can not pull up when you apply vacuum to it.
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I pulled the Accufab apart and did not find a tear in the diaphragm. Looked like the spring was in good order as well.
I also pulled apart the Kenne Bell regulator that I replaced with the Accufab, and did not find anything wrong with it either.
I did notice that the vacuume port on the Accufab is quite a bit smaller inside diameter than the Kenne Bell.
Okay, so now what do I do? Set pressure at 43 psi with vacuume line off and head down the road, or replace with the KB and see if pressure drops when I connect the vac line?
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its not the regulator , its the return line cant flow back what the hotwired walbro is supplying
im sure if you bypass the hotwire at the tank by plugging the pump back into the factory harness youll see the pressure drops
try opening up the return line ends (the opening of the saginaw ends) with an awl or a small drill bit , and check the line at the axle and tank for kinks
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Yep, sounds like the return line. I guess the clue was in one of the earlier posts where you said the pressure would rise under boost but not drop.
Unless the ends are caked up with fuel deposits, there should be no need to enlarge the inside of the fittings. My first guess would be a kinked hose at the axle on the return line or an internal collapse in the rubber line up front where the vertical down line from the regulator makes the 90 deg turn to go to the back.
Another possibility might be that the return line and the vapor line from the charcoal canister were swapped at the tank when a fuel pump change was made.
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its not the regulator , its the return line cant flow back what the hotwired walbro is supplying
im sure if you bypass the hotwire at the tank by plugging the pump back into the factory harness youll see the pressure drops
try opening up the return line ends (the opening of the saginaw ends) with an awl or a small drill bit , and check the line at the axle and tank for kinks
I bypassed the Hotwire and pressure reads 40 psi with the hose off, and 34 psi with the hose on.
Looks like the issue is when I have the Hotwire connected.
So where do I go from here. If I want to run the Hotwire is there an issue if I set the pressure at 43 psi with the hose off?
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You go to what Paul told you and I repeated...loo k for a blockage on the return line side and be sure the hoses are connected properly at the tank end...return line is in the middle as I recall
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if that is not proof that a hot wire works, I don't know what is :)
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Just put the car up and checked the lines. Return line does not have any kinks, and it is connected at the correct location at the tank.
:icon_eyes:
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what about the inside of the two rubber lines and the inside of the steel lines?
You gonna have to find the blockage...you cannot look at the outside and find anything but a kink....take the line loose at the regulator and at the gas tank end and blow thru the line to see if it is clear. Also blow into the end that goes into the tank after you pull the line off. There is another section of rubber lines on top of the tank
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First off, thanks for your diligence in trying to help me figure this out.
If I remove the line that connects to the regulator and to the tank at the rear, and blow air into it, is that not the feed line? I thought this was a return issue.
If the fp drops correctly with the vac line off bypassing the Hotwire, then does not drop when the Hotwire is connected, is there a blockage or is the return line not adequate to handle the amount of fuel being returned under the Hotwire?
Don't know if it's out of line, but I can be reach by phone if it's easier...
717-805-0940
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The return line screws into the bottom of the regulator. the delivery line screws into the front of the fuel rail on the passenger side of the engine. If you follow the two lines down the front of the engine, you will see them come together, make the turn with two rubber hoses, and then run to the rear of the car.
Remove the lower line from the regulator and blow thru it. If the return line is not blocked then it should be more than adequate to handle a 255 lph pump like the walbros. If you installed one of the higher output pumps like the TT pump that Eric sells, then it may not be large enuf.
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the fuel pump sock should be positioned to be pointing long end toward the float ,
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If you installed one of the higher output pumps like the TT pump that Eric sells, then it may not be large enuf.
I blew air through the line and still have the same result with the Hotwire hooked up.
I bought the fuel pump from Eric at TT, it is a Walbro 255.
I can't remember which way I positioned the sock, but I believe it was correct as it's easier to insert he hangar that way.
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Not sure what to tell you as something has to be restricted. I guess drive it the way it is and it will be a bit rich at idle and sort itself out as the speed comes up. Long as the pressure rises properly with boost, that is the crucial thing...
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Performance wise....and for street use, would it be better to bypass the Hotwire?
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If it were mine, I would find out where the restriction is and eliminate it.
If the car is capable of producing enough fuel pressure without the hot wire to sustain the boost you are running, you could remove the hot wire until such time you feel like taking the time to go thru everything. I was hoping that blowing a 100 psi thru the line might open something but I knew that was a long shot unless it was substantially blocked with some debris. You have three sections of rubber hose plus the possibility of a dented line that is restricting flow..and you have the entry into the fuel sender. It takes time and patience to go thru everything.
Wiring is terrible on these cars and I would not, personally, crank the boost up to run alky or other without having full voltage to the pump.