Supplementary fuel regulator. (Car shenanigans)

[Martin Hocking]

Has anyone ever had anything to do with one of these on an engine?

As far as I know it boosts fuel pressure on boost.
Any idea if they are serviceable. I need to actually test fuel pressure to see if it is actually working at all but long term fuel trim is up at 34% at times, the supercharger isn’t standard but this seems a lot!

 

[tigdlo]

Never seen one but it looks like a pressure transducer, if it works the way I think it will, can't tell from the photos, it will output a higher pressure than at the input to feed the standard fuel pressure regulator. If so you could tee of the air vacuum/pressure pipes and check it there too.

What car is it?

 

[Martin Hocking]

Thanks Tigdlo.
It’s a American Ford F-150 from 98.
I sort of inherited it from my dad.
It’s a 4.6 v8 with an Eaton supercharger fitted. I don’t really know the exact ins and outs of it but it’s one of these kits.

http://jimroal.com/Allen/AllenBrochures.pdf

As far as I’ve read they sometimes work by reducing the return flow to the tank. But that seems like it would be fighting against the normal fuel regulator, unless it replaced it.

It has a vac line that comes out of the boost side of the manifold but strangely tees onto the upper and lower portion of the valve thing. I sort of assumed it would be some sort of diaphragm or something.

 

[Martin Hocking]

Right it makes a bit more sense now.
It’s not quite so mysterious, it doesn’t work in conjunction with the existing regulator which the term supplementary implies, it’s a more normal pressure referenced fuel regulator. So it is simply reducing flow back to the tank relative to manifold pressure.
I shouldn’t try and do these things while I’m cooking tea!

Further investigation a bit later on I think…

 

[Martin Hocking]

Sorry the above post should say it replaces the standard regulator…

 

[Pete.]

It's probably a 1:1 rate pressure regulator. I've used both 1:1 and rising-rate in my turbo builds. The rising-rate (also known as a FMU) is a fairly crude but effective way of adding fuel for boost on turbo conversions that requires no electronics. It would have a spring pressure setting to set the base pressure then a bleed valve to increase fuel as the turbo makes boost. Mine made 300hp from an engine that made 175hp before the turbo. You have to be careful with how much boost you us so that the excess fuel pressure doesn't cause the injecotr to lock up.

The 1:1 regulator is used to add 1psi of fuel pressure for every psi of boost. It's function is to prevent boost pressure from acting against fuel pressure at the pintle. If you put say 43psi of fuel into the injector then 10psi of boost from the turbo, your delta-p across the injector is 33psi instead of the normal 43psi. the 1:1 regulator keeps the delta-p at 43psi so that you don't run out of fuelling capacity as boost increases and keeps the injector atomising properly.

They do other rates a well but I have no experience of those.

 

[Martin Hocking]

Thanks @Pete. as always. Excellent explanation, I’d also be surprised if it’s more than 1.1 as I don’t think there’s much boost, more a prevailing gust! It definitely helps, but it only really increases power to what you’d expect from a decent size v8 in the first place. I don’t know what Americans do to engines to make to put out so little power!

Your turbo projects sound very interesting!

I’ll have a proper play this weekend. Change the vacuum lines and test fuel pressure etc.

I still don’t understand why the regulator has two inputs for manifold pressure but hopefully all will be revealed soon enough!

 

[Keithmac]

Have a search for "Rising Rate Fuel Pressure Regulators".

Personally I always use 1:1 regulators (Sytec), the fuel pressure is always 45psi (or whatever you set) in relation to manifold pressure.

This means when tuning you do not have to tune for varying fuel pressure.

The rising rate FPR's are a way around using Superchargers etc on normal naturally aspirated car PCM's that can't "see" boost pressure, not my cup of tea personally.