fuel regulators?!

I've heard before that the stock regulator can definitely handle the flow. Maybe after some bigger injectors and rails, an upgrade would be a good idea.

If you end up going with turbos you'll want to get a rising rate regulator. The stock will be fine for the moment.

Same Question but different

Ok, kida the same question, I just replaced a fuel pump (didn't need to, it was the fuel pump relay... go figure) I also replaced the fuel filter. I used the 255 pump since I was was replacing it anyway. NOW, the car is starving out about 2500 -3500 RPM. Any ideas? It's on my 91 GT conv

Thanks,

If all you did was replace the stock pump and change the filter (and did it correctly), then you have other problems. I would suggest reading through the fuel system troubleshooting post that is floating around this forum.

Vipersix said:

If you end up going with turbos you'll want to get a rising rate regulator. The stock will be fine for the moment.

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The stock regulator is in fact a rising rate (1:1) and unless it's bad, does not need to be changed out at all. Keep it in and spend the money elsewhere.

The stock regulator, or any regulator which has a static pressure increase ratio of 1:1, is NOT a rising rate regulator. By definition, the fuel pressure must increase by an established rate - thus rising rate - as the manifold pressure increases. Mechanically, the regulator monitors the manifold pressure and adjusts the fuel pressure as necessary. For instance, if you set the fuel pressure at 40 psi and there is a slight vacuum in the manifold of -5 psi, the pressure at the rails will be 35 psi. If the manifold pressure increases to 15 psi, the rail pressure increases to 55 psi in order to maintain a static pressure of 40 psi.

The rising rate regulator, on the other hand, will increase pressure at the rails by a multiplier. These are wisely used in boosted applications to avoid the characteristic lean conditions under acceleration. In essence, rather than increasing fuel at 1:1, it may increase the pressure somewhere between 1:3 to 1:10.

Granted, the newer computers are able to better account for this disparity through the O2 sensors, but I would still recommend the use of a rising rate regulator.

Vipersix said:

The stock regulator, or any regulator which has a static pressure increase ratio of 1:1, is NOT a rising rate regulator. By definition, the fuel pressure must increase by an established rate - thus rising rate - as the manifold pressure increases. Mechanically, the regulator monitors the manifold pressure and adjusts the fuel pressure as necessary. For instance, if you set the fuel pressure at 40 psi and there is a slight vacuum in the manifold of -5 psi, the pressure at the rails will be 35 psi. If the manifold pressure increases to 15 psi, the rail pressure increases to 55 psi in order to maintain a static pressure of 40 psi.

The rising rate regulator, on the other hand, will increase pressure at the rails by a multiplier. These are wisely used in boosted applications to avoid the characteristic lean conditions under acceleration. In essence, rather than increasing fuel at 1:1, it may increase the pressure somewhere between 1:3 to 1:10.

Granted, the newer computers are able to better account for this disparity through the O2 sensors, but I would still recommend the use of a rising rate regulator.

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My apologies, your are correct. A rising rate regulator (aka FMU) is one that raises fuel pressure beyond that of 1:1.

There really are only 2 uses for an FMU in today’s computer controlled engines. The first one is purely a band-aid fix to using a fuel injector that is too small for its original design. While many supercharger kit’s come with these, they are by no means optimum and quite often leave you running pig rich under WOT. If they fail….well, your screwed. They push the injectors past 100% DC and quite often destroy the spray pattern at atomization of the fuel. None the less, they do work…but are not recommended.

The other use for them is for those running huge injectors with itty bitty pulse widths. With this allows you to do is run less fuel pressure at idle allowing larger injector pulse widths which would give you a more stable idle. At less vacuum and more boost, the fuel pressure would adjust at the rising rate and give you the proper pressures for the demands of the larger injectors.

I don’t believe either one of these are what the original poster had in mind….therefore the stock regulator should be just fine. Almost all tuners are going to want a 1:1 ratio with the stock fuel pressure settings.

millhouse said:

There really are only 2 uses for an FMU in today’s computer controlled engines.

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I would add a third which I base my recommendations on. It is normally a good idea to run a richer mixture under boost than you see under light loads and idle. As such, unless you have the ability to adjust the enrichment tables of the ECU itself, a rising rate regulator (or FMU if you will) is the only way to accomplish this.

Otherwise, I would agree with your assessment.

Vipersix said:

I would add a third which I base my recommendations on. It is normally a good idea to run a richer mixture under boost than you see under light loads and idle. As such, unless you have the ability to adjust the enrichment tables of the ECU itself, a rising rate regulator (or FMU if you will) is the only way to accomplish this.

Otherwise, I would agree with your assessment.

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Yeah, were pretty much saying the same thing. There is no need to use one if you have the proper injector size and matching MAF meter. At that point, a tune is necessary and a FMU will be of no help. If the injectors are too small to support your horsepower level, a FMU can work. You will not have the ability however to adjust the AFR’s for all load levels….and unless you get a an actual tune, what you get is what you get. You will most likely not have a consistent AFR throughout your load/rpm range with an fMU and small injectors.