Can anyone please tell what a rising rate fuel regulator
achieves on a fuel injected engine?
Roger
Depends which fuel injected system you have. Here is what they do and can be used for.
REGULATE FUEL PRESSURE
Fuel pressure is key for all EFIs. Outside of the newest
systems which adjust timing and even the cooling fan with their 'puters,
most EFI have only one tool to do their bidding...that is the the control
of the duration the injectors are open. The ECU responds to each set of
inputs by opening the injectors for a pre-determined period (the fuel map.
If duration is the only control, fuel pressure must be a given and it must
be high enough to create a very fine spray through the injectors. The regulator
maintains the pre-determined pressure and returns any fuel unnecessary
to that task back to the fuel tank.
(More than any other single thing about them, the advantage of any FI system is the fine super combustible air/fuel mixture it creates. The programming can be great..but it is normally used to obey emission laws and reduce warranty claims rather than produce power.)
RISING RATE
At times, in demand situations such as high acceleration, the engine needs more fuel. Rather than program a second set of fueling parameters to deal a special situation, one can take another route to the same place by using mechanics rather than ECU programming. In this case, these regulators are used. By having it react to engine vacuum (hose to the plenum), you can have it increase or decrease the fuel pressure on demand. In doing so, you are injecting more fuel though the injector duration remains the same.
AFTERMARKET ADJUSTABLE RISING RATE FUEL REGULATORS
Let's call one of these a "FSE" as this is the maker most often fitted to our engines after the fact. A FSE has a sharper curve upwards in responding to vacuum changes. In other words, it increases fuel pressure at a faster rate than stock and therefore give your acceleration a bigger "kick in the pants" than the stock rising rate fuel regulator
ADJUSTABLE
The fuel pressure the FSE maintains can be adjusted in
a very large range. For a digitally operated EFI system that means that
anomalies in the regulator pressure can be refined. (Stock regulators can
vary a bit and an adjustable regulator weans this out with a slight turn
of an adjuster.) Beyond that and the acceleration kick they cannot do much
much for digital (Hot Wire etc) systems. Raise the pressure too much and
the inputs of the system pick it up and adjust for it or simply go into
"limp home" mode.
HOWEVER, a simplistic Flapper system, an analogue computer with few inputs and no controls on emissions, adjusting the fuel pressure adjusts the fueling..aka reprograms the car. Very handy for the race track and engine upgrades.
Here is a more concrete example. Let's say you were increasing your capacity from a Rover 3.5L to a LR 3.9 or 4.0L (3528cc to 3947cc) or an increase or 11.8%. In doing so. you will have "leaned out" your fueling by that amount. Your ECU can still run the engine, but it is no longer optimum..and may have a tendancy to overheat.
As well, you would not see much advantage (a bit more
torque) in the extra capacity as there would be nothing more going into
the combustion process. The situation would be analogous to the Morgan
stock Plus 8 4.6s, where 3.9 fueling was used with them. The bhp rose negligibly
(4 bhp) rather than the extra 28 bhp 4.6s produced in other vehicles with
the proper fueling.
With a digital system, reprogramming would be called
for. However, with a Flapper, one can simply increase the fuel pressure
with a FSE.
Ideally, once can do even better than that..over time
as well. Find a way to increase airflow a bit more, a
K&N/Superflare trumpets OR a Jaguar AFM. In any case
the "programming" is evident assuming the same injectors before and after.
Simply increase the fuel pressure 12%, then re-tension, the spring wheel
in the AFM until the C02 reading at the exhaust at 850 rpm is 2%ish. Then
set your idle at 1000-1050 rpm.
If other major components are changed, one must rely on trial and error. However, in every case it is the FSE and the AFM that will solve the problems.
Lorne
P.S. Opening up a L-Jetronic AFM is considered taboo.
Definitely there is a bit of risk to it..but none that
ever
stopped me. One must take care of the way one outs the
cover
back on. The wrong sealant and the AGM can fail.
http://www.gomog.com/allmorgan/AFMadjust.html