"EFI" regulators and key-off pressure

[blindsquirrel]

It seems to me that it should be obvious that an aftermarket fuel pressure regulator advertised as "EFI" should hold pressure at key-off just like a stock EFI system, but apparently the people who make go-fast parts didn't get that memo and a lot (most? all??) of the regs on the market don't do that. Worse, very few of the makers care enough to give specs on their products that would allow a buyer to easily tell ones that do hold pressure from ones that don't, and it's a complete crapshoot as to what you'll get for your money.

Aeromotive is good stuff, right? They know what they're doing? Their FAQ says:

6.) I?ve installed my new Aeromotive bypass regulator. Fuel pressure seems to adjust fine and holds great when the engine is running, but when I shut the engine off, pressure drops quickly to zero. Shouldn?t the pressure hold like it did with a stock regulator?
No, Aeromotive EFI bypass regulators may not seal perfectly when the pump is off. They are engineered for the highest possible performance when the engine is running. OEM regulators must hold pressure for 30-minutes after shut-down to pass EPA emissions standards. At Aeromotive we know our customers priority is to have the best possible flow and pressure control when the engine is running and we don?t compromise this standard to force the regulator to seal when the engine is off. If extended crank or hard-start becomes a concern, first allow the pump to run and prime as long as possible after turning the key to the run position, then start cranking the engine, just before the pump shuts off. If the priming cycle is too short to allow the engine to start easily with this approach, extend the priming cycle in the ECU if programmable, or ad a timer board or momentary button to the fuel pump run circuit.

JFC. OEM regulators are not holding key-off pressure strictly for emissions reasons; they are doing it because FUEL AT ZERO PSI IN A HOT FUEL RAIL BOILS OFF TO NOTHING every time you have a hot-soak. This is Not Good. Not good for the injectors, especially. This is why the OEMs do it, because that's how EFI should work, not because of emissions. If you do it WRONG it increases emissions, that's not the primary reason for doing it *right*.

Can anyone with first-hand experience recommend a regulator that's verified to work like it should so I don't have to waste several hours trying to get info from manufacturers, assuming they'd even know? Universal style, -6 in/out is fine, should be able to deal with the bypass needs of a typical 450LPH intank pump. Nothing special. Just needs to be a proper EFI regulator and not a carb regulator with a big fat spring in it.

/rant over

[blindsquirrel]

AEM replied to my email query by... pasting the exact same section of Aeromotive's FAQ that I quoted above. No joke.

[radrace19]

It seems to me that it should be obvious that an aftermarket fuel pressure regulator advertised as "EFI" should hold pressure at key-off just like a stock EFI system, but apparently the people who make go-fast parts didn't get that memo and a lot (most? all??) of the regs on the market don't do that. Worse, very few of the makers care enough to give specs on their products that would allow a buyer to easily tell ones that do hold pressure from ones that don't, and it's a complete crapshoot as to what you'll get for your money.

Aeromotive is good stuff, right? They know what they're doing? Their FAQ says:

JFC. OEM regulators are not holding key-off pressure strictly for emissions reasons; they are doing it because FUEL AT ZERO PSI IN A HOT FUEL RAIL BOILS OFF TO NOTHING every time you have a hot-soak. This is Not Good. Not good for the injectors, especially. This is why the OEMs do it, because that's how EFI should work, not because of emissions. If you do it WRONG it increases emissions, that's not the primary reason for doing it *right*.

Can anyone with first-hand experience recommend a regulator that's verified to work like it should so I don't have to waste several hours trying to get info from manufacturers, assuming they'd even know? Universal style, -6 in/out is fine, should be able to deal with the bypass needs of a typical 450LPH intank pump. Nothing special. Just needs to be a proper EFI regulator and not a carb regulator with a big fat spring in it.

/rant over

I thought it was more related to the fuel pump not having a check valve being the problem and not the regulator. Am I mistaken?
-Greg

[Alvin]

I've tried to make swap cars and such more dirveable by adding a check valve. Which works with a aftermarket regulator which to me indicates the bleed back is mostly a pump issue....

BUT....

It didn't work in the end. I know you think the pressure will help it from boiling in a hot rail but that isn't the case. If it's like coolant you only get about a degree raise in boiling temp per pound and boiling temp of gas is already super low.

I had to pull these check valves off because every one of them would vapor lock. Go to start the car and get nothing.. Look at a fuel pressure gauge and it would be more than 80-90 which is where most injectors stop opening

[blindsquirrel]

The stock returnless system holds rail pressure throughout a hot-soak. Why does building a system that behaves the same, with a single-inlet returnless-style rail, a regulator that blocks the return path at key-off and holds pressure, and a pump with an internal check valve that blocks any bleedoff through the supply path, give bad (or even different) results?

[blindsquirrel]

A single inline check valve in the feed, between the regulator & rail, would mean the regulator doesn't have to seal off the return, and the tiny little check valve in the pump can go away too.

Though I still don't understand how a regulator with a proper hardened and ground seat would 'compromise performance'. That really only makes sense as an excuse to not build a proper EFI regulator. Maybe China doesn't know what 52100 steel is?

[Alvin]

The stock returnless system holds rail pressure throughout a hot-soak. Why does building a system that behaves the same, with a single-inlet returnless-style rail, a regulator that blocks the return path at key-off and holds pressure, and a pump with an internal check valve that blocks any bleedoff through the supply path, give bad (or even different) results?

Have no idea.. Happened with more than a couple builds before we ditched it. Try it.. maybe it will work for you.

[TheMechanic]

Totally agree. Rest pressure is a way I have been diagnosing systems for decades. If it doesn't hold pressure I block off the pump to see if it is the little rubber check valve in the fuel pump. Otherwise regulator, external leak or leaking injectors. Biggest problem with long crank. A while back I was contemplating a dual factory style fuel system with a pressure switch that would activate if pressure dropped below "X" to create a secondary fuel pump when supply demands it. I have set up several dual pumps for off road vehicles as backups due to VERY harsh environments.

[blindsquirrel]

https://www.fuelab.com/84801-in-line...heck-valve/p96

I guess if regulators were built to seal the return port like stock, the aftermarket would get to sell a lot fewer $200 add-ons...

[blindsquirrel]

Have no idea.. Happened with more than a couple builds before we ditched it. Try it.. maybe it will work for you.

OK, I think I've figured out the issue. Say you add a check valve after the (leaky aftermarket) regulator. Two things have to happen at once to get a no-start/vapor lock. One, boil off fuel in the rail. Two, have the rail pressure rise to higher than the regulator set point. On engine cranking/pump running, all the supply volume will bypass back to the tank, and the check valve will remain closed and no fuel will flow to the rail. And injectors don't work very well when you put vapor to them, even if the pressure is high (edit: even if low enough that they aren't locked closed).

Bleeding off rail pressure to somewhere less than the regulator set point would allow the supply pressure to open the check valve and get things working again.

I wouldn't be surprised if a condition like that could be caused by a specific fuel blend.

[blindsquirrel]

AND, the above condition doesn't happen if the sealing takes place inside the regulator at the seat, because any pressure rise in the rail during a hot soak is bled off thru the return path. The regulator bleeds off anything above the set pressure no matter the source, pump running or not.

THIS is why I would much rather have a real EFI regulator with a real proper hardened and ground seat that seals the return path like an EFI regulator is supposed to.

[TheMechanic]

I'm not paying $200 for a fuel filter that need regular replacement.
I use these on the off road truggies and also some of my Detroit Diesel big engines.
https://ph.parker.com/us/en/valves-c...00-series/2650

[blindsquirrel]

Well, the filter element is about the same size as the 'non-serviceable lifetime filter' in my stock pump module, and the same 10 micron paper, and my stocker is 16 years old and 215k miles and from all indications still doing fine. I'm sure it's not exactly pretty at this stage, but it's not plugged up yet.

[blindsquirrel]

I love Delrin.

fpr-plug.jpg

And lathes. Delrin and lathes.

[blindsquirrel]

20220514_095300sm.jpg 20220514_095107sm.jpg

If I have issues with this, I'll make a hardened & lapped seat insert for it.

[gametech]

Since this is one of the google results when searching this topic, I will resurrect this thread with the fact that I found an Edelbrock efi fpr that says it will hold pressure for at least 20 minutes. Not sure if I want to spend $200 to find out, though. For now I just put a delay on my initial prime pulse so it happens after my rails pressurize.
edit-- Tried it, and it bleeds pressure. At first I thought it was my cheap Vibrant brand check valve at the fuel pump, but if I cap my regulator return the pressure holds. Time to take apart the brand new regulator and see if it can be made to hold pressure.