fpr & settings
 

hey guys w/ adjustable fuel regulators

i am thinking of purchasing an adjustable fuel regulator but there is one thing i don't understand. how can you tell what the optimum fuel pressure is? do you have to go to a dyno and just keep changing till you hit the highest hp & torque number or do you get and air/fuel ratio gauge and target one specific air to fuel number to get the most out of it. I guess that is the reason i never purchased one, but with all these people doing this fine tuning it seems a few hp and a few ft/lbs of torque could be found with one of these. please guys steer me in the right direction here

yes, you really need to go to a dyno with a wide band o2 sensor to find the "perfect" setting. but you can get it in the ballpark if you just read your spark plugs (and running charectoristics). its really not too difficult.

get a kirban!~

take care,
adam

You do not use an adjustable fuel pressure regulator to change your air/fuel ratio. That can only be done with a chip. You can, however, use fuel pressure to compensate for injectors that don't have enough capacity for the amount of horse power your engine is capable of producing.

Changing fuel pressure can cause measurable, temporary changes in the A/F ratio and performance of your engine which ta dyno will pick up, but the computer will compensate for the addition or removal of fuel by using the readings coming from the O2 sensors.

There are exceptions to this, of course. Anyone who has seen an a/f gauge in action knows that the thing constantly bounces back and forth between rich and lean. I think this is because of the timer resolution used to control how long the injectors are open. The computer just makes sure that the bounce occurs between a predefined rich and lean level so that it averages out to be the stoichiometric a/f ratio of 14.7:1.

Think of this range as two lines on a table that are 1 foot apart. One line is the maximum richness allowed and the other line is the maximum leanness allowed. The actual a/f ratio can be represented by a pendulum. It swings back and forth 8 inches and is positioned between the two lines on the table. Optimally, as far as having a perfect, stochiometric a/f ratio, the pendulum would only go within 2 inches of either line. As you increase fuel pressure, the pendulum would come closer and closer to the max richness line. As long as it doesn't cross that line, the computer will not do anything to correct it. If, however, it does cross the line, the computer will compensate by removing some time from how long the injectors open and that will move the pendulum back between the lines. It does this over time but will eventually negate any adjustment that you made.

What I just described is how closed-loop mode would work. Any adjustments that the computer makes are stored in the KAM and factored into the calculations used during open-loop mode.

Is that right jimberg, about the a/f ratio not being controlled by the AFPR? I didn't know that. I guess I'll save my JMS chip then for when I get dyno tuned.....I was gonna sell it because I didn't think it made a difference w/ the a/f mixture. Thanks.

You're welcome. AFPRs serve a purpose, but a/f ratio isn't one of them. When you're dyno testing, you may find that your power flattens out early and your a/f ratio goes lean at the same time. This indicates that you are running out of fuel on the top end and you need bigger injectors. Maybe not big enough to go to the next size up, though. You can increase fuel pressure to increase the capacity of your fuel injectors.

hey Jim-

I used an adjustable so that I could knock the spring setting back at an idle. When I had the 218/230 I couldn't get the idle to lean out w/o backing the spring off. I just didn't have enough vacuum. My duty cycle just went up at WOT. The closed loop would bounce all over the place and still couldn't correct. I guess this isn't a normal application?

thanks avbcon12 and jimberg for the responses.

5cu11y, I guess I'm not clear as to what you mean. Could you go into a little bit more detail?

Briand, you're welcome.

Just a footnote to this..

'5.0 Mustangs and Fast Fords' recently tested an AFPR on a stock Mustang, and found that by lowering the pressure by 4-6 psi (down to 28 psi) the car actually responed with an extra couple of horsepower. It seems that the factory computer is set to supply enough fuel to prevent any chance of detonation, etc. with stock settings. In some cases, maybe a little too much fuel.

Take it for what it's worth...

I had a cam that was 218/230 duration. At an idle my manifold vac. was down to ~10 Hg. My pressure regulator was referencing this lower vac. and was letting more fuel through. At an idle, it was not possible to trim the fuel back any more, so I was running very rich. I bought an adjustable regulator, and set it lower so that the 10" vac. would put me back where I wanted to be. Not so rich.

Unless they drove the car around a lot between adjusting the fuel pressure and putting it on the dyno, I wouldn't give the test much credence.

It is possible to limit the amount of fuel available at WOT by lowering fuel pressure, but it isn't something I would recommend. Burning a chip would be a much better and more precise way to do it.

What do you mean driving around a lot between adjusting FP and putting it on the dyno? Which test?

If the injectors are running at a minimum, how do you lean them further?

5cu11y, my response was to magicmerII. I'm still thinking about what you posted. You must have entered it at the same time I responded to magicmerII.