Everyone just a question that I have becuase I don't know the exact answers so I wanted to ask for them.

What issues do you get into that clue you in that you need to upgrade the fuel rail? How good is the stock Rail? If any issues from it what have you seen?

What issues do you get into that clue you in that you need to upgrade the fuel pressure regulator? How good is the stock FPR? If any issues from it what have you seen?

I think several of us don't know exactly the correct answers so please shine the light for knowledge reasons.

Thanks in advance.
GTVEVO

 

I have always been told that stock fuel rail is golden. And the only reason to get an aftermarket FPR is to "fine tune" the fuel flow.

 

Here's what I do know about the stock FPR. It works fine with the aftermarket Walbro 255lph pump. However, your fuel rail pressure will be significantly higher. Normally, according to the service manual, when running the stock fuel pump the rail pressure should be ~43.5psi with the manifold reference line disconnected. My personal experience with the Walbro 255 has been that base rail pressure runs ~52psi. I'm not sure if the FPR or the recirculation line is being overflowed or my car is just an oddball.

Anyway, the higher fuel pressure means that a fuel injector rated at 550cc/min @ 43.5psi will flow more like 600cc/min @52psi. Or in my case, the 660s are flowing the same volume of fuel as 720s.

Regardless, the "thru the mail" Dynoflash I have compensates for the higher pressure with no issues that I can discern so I don't think my car is unique in regards to the higher fuel pressure resulting from a larger fuel pump.

 

The stock fuel rail is good for 500 plus whp

The main reason to upgrade the rail is to be able to easily add huge -AN fittings on the ends for large fuel lines when you get to 1,000 injectors and 600 plus whp

A fuel pressure regulator is always a good idea - (a good one like aeromotive) - pruven makes a lovely bolt on kit that goes right onto the stock rail. However, the change to the fueling delivery is so radical NONE of my base maps will ork and you will need a full custom tune.

I would not run a stock fuel pressure regulator on my car after watching the way my fuel pressure gauge works with the stock one vs. the aeromotive one

 

When you say radical. Are you saying that the changes in fuel delivery take affect much faster? For example my fuel system doesn't recover as quick as I would like it too during spoolup recovery after a shift on a WOT run down the track. It isn't causing issues it just isn't as exact as I would like. This is after the Accel fueling has done its job and while boost is climbing. My fuel upgrades are only 850 cc injectors and the Walbro255. (stock rail and FPR) I run the AEM for management though.

For example, Shifting out of 1st at 7k into 2nd recovers in the mid 5k area and when the MAP pressure rises to about 7psi I am running about 13.5afr then at 9psi maybe 12.5 afr then about 13 psi it will get back into high 11's. But on a wide open pull it is 11.0-11.2 at all bost levels from 3.5k on up to redline. So I am pretty sure is it the FPR no reacting as well as I would like for it too. Is this possible?

 

I'll take a stab at what Al is saying. All of Al's base maps with the 255 pump mod already basically assume a rail pressure of 52psi. Any changes to rail pressure would basically mean that he'd have to rescale for a different size injectors. This requires a custom tune. I may be wrong but I don't think the "radical changes" he is referring to have anything to do with throttle response.

In your case you could rescale using the AEM EMS with no sweat. As you may know, the EMS has a "wizard" to step you through the rescaling process. It takes a few mouse clicks. Simply tell it the size injector and base fuel pressure your current map is using and then tell it the new, lower fuel pressure and injector size. It will automatically rescale the fuel maps.

One thing to bear in mind is that *if* you are currently running high injector duty cycles (>75%) with your 850s @ ~52psi, your IDCs will be even higher at 43.5psi. By my reckoning, your duty cycles will be about 9.3% higher, however I may be mistaken. Regardless, you need to make sure you don't run the injectors too much above the widely accepted maximum safe IDC of 80%.

I wouldn't screw with ANYTHING until you get a handle on what your current rail pressure is. Once you've got that bit of information then you can scale for the change in fuel pressure and it's resulting effect on fuel volume. If you don't do the scaling correctly you could run lean and grenade.

 

I understand how fuel pressure changes the amount of fuel that is injected at any given rpm or pressure level. I also understand that lower fuel rail pressure will cause the injectors to work harder to get the disired amout of fuel raising the duty cycle. This is all in my grasp and everything I have is callibrated/recaled and set so I am just trying to figure out what issues others have had with the stock FPR and or Fuel Rail so many of us will know when to upgrade.

Above I discribed one thing that doesn't sit exactly well with me but their are so many varibles that it could be. It is somthing that I am trying to troubleshoot to be a little proactive. But for the post I just wanted to shead some light on what issues you would see that would cause you to want to change the Fuel Rail or FPR and I could take this into consideration as well.

 

Sorry, I think I now understand what you're saying and asking.

I don't think anyone really knows the actual limitations or failure modes of the stock FPR. At least I haven't read anything here. Al's comments above are the first one's that I can recall regarding the reliability of the stock FPR that have been made by a tuner. It wouldn't surprise me if others have said it before but I haven't read it.

It sounds like the first step is to install a fuel pressure sender and actually log some data with the stock FPR and see if it actually has issues with responding to pressure increases. I guess if there are lags in fuel pressure that coorespond to lean conditions then you've got an issue. I'm definately interested in seeing some good log data to support any issues.

 

Ok ya I am going to do some testing on the injectors first to make sure they are reacting with the correct pulse width and duty with in my map cals to make sure they aren't falling behind. Then after that conclusion I will probably be getting a FPR with a port so I can log the fuel pressure results on the AEM and see the changes in it at certian points. I know that people have actually used the EGT input to trim up the injector cycle to compensate for fuel pressure loss but I wanted to get some rock hard evidence first. I would think that I could do this with Load Accel trims as well so I will be doing lots of testing to find my issue and put together my action plan.

If anyone else has any results in FPR or Fuel Rail replacement please share them along.

Thanks.