Fuel Pressure regulator ! Good mod ?

[lavapearl]

The dealership mechanic told me that stock pressure is about 36 psi, He told me that he raised it to 46 psi, The more psi the more HP ?

[TraceZ]

My understanding is that is not a good idea. I'd like to hear what others have to say about it. If you increase the amount of fuel pressure in the fuel rail, that will make the injectors introduce more fuel based on a constant pulse width. The PCM should see this rich condition and shorten the pulse width to maintain proper air fuel ratio. The end result - no change except for the fact the fuel pressure is messed up.

I would say that you should run whatever pressure the injectors are designed to run. If you want to add extra fuel, you need to do it via the PCM and some tuning. I would think that changing the pressure on the injectors is like changing the injectors themselves. They will now behave differently. You'll need to have the PCM reprogrammed to take advantage of the change.

My thoughts would be to run the stock injectors at the stock pressure. We'll see what others have to say, but I dont think you are gaining anything by turning up the pressure, and you may actually be hurting yourself because the PCM no longer has an accurate description of the fuel system it is managing.

I do know for a fact that changing the injectors requires reprogramming. I would think that changing the pressure on the injectors would necessitate the same reprogramming because that changes the behavior of the injectors. Injectors flow a set rate at a set pressure. Change either one and you effectively change the system.

[Rob B (shoebox)]

Unless you are running speed density only or have other fuel system mods (like bigger injectors) that require some possible change in pressure, it is not of any value. By virtue of the O2 readings, the PCM will eventually change the injector pulsewidths to compensate for the pressure change as Trace said.

[95TransAm]

I currently am a student at WyoTech and have already passed engine management systems.

I fully agree with the above statements.

[Injuneer]

The dealership mechanic told me that stock pressure is about 36 psi, He told me that he raised it to 46 psi, The more psi the more HP ?

Tell us more about the car.... what year, model, engine, any mods??????? Without that basic info, everyone is just guessing. Looks like an LT1/WS6 in the photo, so I'll assume that.

If its a 94-97 LT1, stock fuel pressure - without the vacuum compensation line connected - is 43.5psi, although the specs allow it to range from 41-47psi. With the vacuum line connected, at closed throttle the pressure will drop 6-8psi into the 30's. When you increase the pressure to 46psi (and we'll assume that was measured with the vacuum compensation line attached), you increase injector flow by about 9%. In repsonse, as Shoebox has pointed out, in closed loop the PCM, based on O2 sensor feedback, decreases the long term fuel corrections (BLM's) from 128 to 115, restoring the A/F ratio to exactly the 14.7:1 that the PCM is programmed for.

In that situation, when you go to WOT, the PCM ignores the BLM's and adds 9% extra fuel, making your WOT A/F ratio even richer than it already is, causing you to pour out black smoke and lose power. The stock "target" A/F ratio is already way too rich on the LT1 (~11.7:1), so increasing the fuel pressure really screws things up.

If you have a 93, there is some speculation that the ECM has a slightly different logic, and allows the changed fuel pressure to somehow avoid correction by the ECM, but I've never seen any firsthand evidence to support that.

If you have a 98+ model LS1, the stock fuel pressure (no vacuum compensation) is 58psi, so by setting it to 46psi, he reduced fuel flow... BLM's go up, yada yada. Hopefully you see why you need to add a "signature" to your posts, showing basic info about your car.

Short version.... adjustable fuel pressure regulators, in most instances are a waste of money. You tune in the PCM, not by screwing up the fuel pressure.