i just dont understand why buy one cause you would have to have so computer tuning to run one properly am i correct.im going to get pcm for less in a few weeks can brian tune one in for me and will there be a hp diff like when u put one on a mustang sorry to mumble on just was always confused by this thanks again everyone randy

 

Well, a adjustable fuel pressure regulator (AFPR) just controls the pressure of the fuel going into the injectors. By lowering pressure you lean out your mixture which makes more powerr, but after a bit of driving your PCM notices the mixture has been lean and compensates by making the injectors firing for a little longer, thus making your car run with the same air-fuel mixture as stock.

You can get greater power by programming your computer to have a different "ideal" air-fuel mixture. Unless you're running a huge cam, nitrous, or a blower, you usually don't even need a regulator to do this. Brian should be able to just program the PCM to run leaner.

FYI, the reason that you'd "want" an AFPR is for situations like forced induction where you need to get a ton of fuel in your engine (in that case, you'd want bigger injectors too).

I'm probably going to get one before I go to dyno-tune my car. If it turns out to be necessary I can just install it. If not I'll sell it.

--Trax

 

Hehe...I love when people say the FPR will be "cancelled out" by the PCM. The only job the PCM has is to adjust part throttle driving so AFR is 14.7:1 and to make sure your car is safely fueled during WOT. If you increase FP, you are effectively making the injectors "bigger" thereby making the engine run richer. If you decrease it, you lean it out.

The computer will "see" this when the O2 values all of sudden shift from more or less fuel - it than "cancels" it out to get proper AFR. This is done during part throttle driving.

NOW, you can lower FP and that will also lean out your AFR at WOT - this will increase performance by running a leaner mixture. One wonders why this is "learned" away as well considering there IS no learning during WOT. The answer is that it really ISN'T. There is a safety feature in the PCM that says if the BLMs are ABOVE 128 (adding fuel) during part throttle driving, it will ADD this additional fuel to WOT. This doesn't work the opposite way though. If BLMs are below 128, the PCM will not pull fuel from WOT fueling.

This is the reason the gains in performance disappear and also the reason why you should always tune the car to be slightly under 128 BLM part throttle. Of course, one can always use "WOT Blocker" (written by Christian Millard) to force the PCM not to add fuel at WOT even if the BLMs are above 128.

There are 3 reasons I see that you'd need an AFPR :

1. You added an aftermarket fuel pump and it increased fuel pressure above stock levels.

2. You have a supercharger/turbocharger and you want to compensate for fuel pressure lost due to the positive pressure in the manifold. Aeromotive makes such a unit.

3. You are running injectors that are too small causing your duty cycle to go above 95%. You can compensate by throwing more pressure at them. Of course, the right answer is to get bigger injectors.

Hope that explains it. And if I made a mistake, I'm sorry...I'm tired.

-Alex

 

Good Post Alex It is interesting how few people really understand how our computers work. I have had to argue out of so many conversations on how fuel pressure affects our cars.

 

This only works on earlier cars, 94+ the computer will compensate with BLM adjustments. So if you wanted a specific fuel pressure to exactly know your injector output, or some other reason, then you have a reason to buy one.

BLMs during part throttle/closed loop driving, affect WOT calculations.

 

Alex...

I'm a little confused by your post... you seem to get it all right, and then come to the (seemingly) wrong conclusion. You appear to be arguing throughout the post that you can beat the system with an AFPR, then correctly state that you can't because the PCM will use the part-load BLM data at WOT.

The only way to gain HP on a relatively stock engine is to lean out the overly rich 11.7:1 target A/F ratio (typical value, but can vary) calculated from the PE tables at WOT. And the only way you could lean things out on a relatively stock engine would be to reduce fuel pressure. And when you reduce fuel pressure, you are driving up the BLM's to the point where they will be above 128, and will affect WOT operation.

Not sure I understand how you "tune" the BLM's down below 128 with an AFPR, while still cutting fuel pressure - won't work. So, you must be tuning them down with something like the MAF sensor calibration table. If you have the resources to go into the PCM and adjust the table, why wouldn't you just correct the WOT target A/F ratio by tweaking the PE tables?

Not sure I understand the point of your whole post.... but I may have just not read it clearly. Any clarification would be appreciated....

 

Sorry, I missed your reply and am getting to it now. Let me see if I can clear this up.

Quote:

The only way to gain HP on a relatively stock engine is to lean out the overly rich 11.7:1 target A/F ratio (typical value, but can vary) calculated from the PE tables at WOT. And the only way you could lean things out on a relatively stock engine would be to reduce fuel pressure. And when you reduce fuel pressure, you are driving up the BLM's to the point where they will be above 128, and will affect WOT operation.

Completely true and that is, what I think, I said. The only caveat I put is there IS a way to defeat this safety feature by using a program written by cmillard. Of course, what is the point of doing this because it would mean you could program the PCM yourself and simply adjust the PEvsRPM table accordingly.

Quote:

Not sure I understand how you "tune" the BLM's down below 128 with an AFPR, while still cutting fuel pressure - won't work. So, you must be tuning them down with something like the MAF sensor calibration table. If you have the resources to go into the PCM and adjust the table, why wouldn't you just correct the WOT target A/F ratio by tweaking the PE tables?

Exactly what I should have mentioned in the original post (and I mentioned above) but neglected to. I apologize, I did say I was tired. As for HOW it's done, Christian has the ability to take a bin file and hex edit it so that the PCM will NOT adjust fueling for WOT if your BLMs are above whatever limit it decides it needs to start adding fuel to WOT. This was dubbed "WOT Blocker". Again, pointless to try to adjust AFR via a AFPR if you have access to the PCM.

Quote:

Not sure I understand the point of your whole post.... but I may have just not read it clearly. Any clarification would be appreciated....

Hope that clears it up. I was just trying to get the word out on how fuel pressure effects BLM and WOT fueling as it really isn't voodoo.

-Alex