Ummm.....PVD04 was right. I think you are the one that is lost.

The fuel pressure regulator is their to keep the effective fuel pressure a constant 43.5 psi in relation to the pressure in the intake manifold, whether under boost or vacuum.

The injector will always be operating under 43.5 psi of pressure. If the pressure goes up with 20 psi of boost, the fuel pressure goes up 20psi to 63.5psi. If the pressure is negative (vacuum), like at idle, the fuel pressure is dropped to compensate, so the injector still operates at 43.5psi of effective pressure. That is what the FPR is there for.

You disconnect the vacuum line to the FPR when setting base fuel pressure because you are setting the base pressure, without any vacuum (negative pressure) or boost (positive pressure) acting on it. Disconnecting the line is basically disabling the FPR from doing it's job. Once the vacuum line is reconnected, it now can do it's job of lowering of raising the fuel pressure 1:1 with manifold pressure changes.


Eric

 

Ummm bostonhatcher
First Fic's will flow differently than PTEs, rochesters, MSD, etc.
Your theory would be close if in fact two variables in your equation were constants.
One, factual Injector flow at actual operating pressures and two, if ALL injectors were made by the same manufacturer.
The scaling values of just the two popular units made by FIC and PTE will be COMPLETELY different. Along with VERY different latency values as well.

Now the theory about scaling your injectors a bit smaller is sound. As it seems to keep the trims pretty stable on CERTAIN cars.
Another thing to note is EVERYONE is basing their findings off a wideband output. No one has taken any injection and cam phasing into consideration. Those two things are the reason why EVERYONE has different values for both CC and latency.

It isn't rocket science, but it is a bit more complex than just your simplistic mathematical calculation you posted above.

 

A fuel pressure regulator does not keep a constant 43.5 psi.


No, your injector operates at whatever fuel pressure is in your rail. Most injectors are RATED at 43.5 psi of pressure.

Let's say an injector is working at 50% duty cycle at 43.5 psi. If you were to turn fuel pressure up on your regulator (or boosted your motor) and the injector duty cycle was the same (50%) then it will squirt more fuel. Injectors work at whatever fuel pressure the rail has.

 

Yes, I know there are no two snowflakes alike.

Using ECUflash, you need to scale down the injectors. It's just the way the software works. Scaling the injectors down is not car dependent, but depends on which software you are tuning with. With something like AEM EMS, it can read fuel pressure by telling the software that you have a 1:1 fuel pressure regulator and it can match the the fuel pressure up from the MAP sensor reading. You tell it what injectors you are running, it already has injector specific latencies, and it does the scaling for you, from the AEM 3.5 or 5 bar MAP sensor.

 

You still aren't getting it. When you have 20 psi of boost in your intake manifold that is 20 psi keeping the fuel from coming out of the injector. If you did not have a 1:1 fuel pressure regulator then you would have 43.5psi pushing against 20psi, which is where the effective pressure of 23.5psi comes from. The reason you have the 1:1 FPR is to increase the fuel pressure with the intake manifold pressure and maintain that 43.5psi effective pressure (20 psi in the intake manifold pushing against the 63.5psi in the fuel rail results in 43.5psi across the injector). Just think about it for a bit. If you still think I'm wrong, think about it a bit more. Repeat until you understand that this is correct.

-Paul

 

Re-read what I wrote and what PVD04 wrote above until you realize that you don't know what you are talking about.

Then I will accept your apology.


Eric

 

So the AEM scaling file that Ivan_C posted lists RC1200 injectors. How come its scaling graph looks so different than the others? I also hear that it's near impossible to get gas to idle with these large of an injector. I want to go this size for E85 on FP Green, but also want to go back to gas if need be.

 

every set of AEM scaling that was posted that i have tried do not work... maybe with the AEM, but as they are listed there, with ecuflash, they arent doing anything for me and the scaling i normally use is nowhere near them.

 

bostonhatcher,

What l2r99gst and PVD04 are saying is correct!

The purpose of a FPR is to increase the absolute rail pressure in order to compensate for the additional boost.

This is simple fluid physics.... 43.5 PSI Fuel Pressure - 43.5 Boost Pressure = 0 Differential Pressure

With 0 Differential Pressure there is no flow of fuel! Period!

 

i dont think he is going to chime back in .... its ok... its a foot in mouth type thing

 

What in gods creation are you talking about?

It is setup dependent. NOT software dependant. We are talking about ECUFLASH and the stock computer. NOT AEM.

I have never seen any AEM that reads fuel pressure and then the end user telling the computer you have xxx fuel pressure regulator. That is absolutley the most ridiculous post I have ever seen ...ever...

It does the scaling for you? from the map sensor? Holy cow.

 

But if floats your boat, here are a few friends that agree with you.

 

Yeah, that was about the wierdest post I have seen yet on here. Nothing like posting 100% wrong information in a thread made to help people.

 

John,

So you found that the scaling of 914 worked well with the FIC1050's? I just put my new FIC1050's in the car Wed night, and have been struggling with the scaling ever since. I had them scaled to 1180 or something wierd like that only to tell myself something else is wrong. I have no clue why this happened, but after changing injectors, my FPR was reading only 25 psi at idle. (Factory service manual calls for 32.5 or something like that) Argh, I was having to screw around with the scaling of the injectors due to the FPR not being set correctly. (After changing injectors, why the hell would the FPR change? I never touched it)

This morning before I came to work, I adjusted the FPR to 32.5psi at idle, and the fuel trims are adjusting themselves now.

So, since I haven't done this in awhile, and to make sure I am on the right track, please correct me if I am wrong with any of the following:

If both fuel trims are reading in the negatives, the car is taking out fuel, and I need to go down on my scaling to add more fuel?

(With resetting my FPR, my Fuel trim Low was -8.5276, and Fuel trim Mid was -3.0368. This was only after a 8 mile trip though, so they are still probably adjusting themselves.)

But, with them both in the negatives, my scaling needs to go down, right?

Scaling down adds more fuel, and up scaling takes out fuel?

Negative trims means the car is taking out fuel, positive means it's adding fuel?

Like I said, it's been awhile since I have done this.