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Old 08-31-2013, 12:04 PM   #1
pdiddy

 
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fuel pressure/duty

I am curious how everyone that is FI is reading there fuel pressure through the rpm range and how they are determining if they are dropping off are you data logging or what to determine this I had my car dyno tuned but only say the AF ratio and the hp/tq numbers and nothing more. I want to be sure everything is and stays good as I continue to do more to my car.
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Old 08-31-2013, 01:11 PM   #2
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I tried logging it with SCT and none of their equations worked for fuel pressure. Now i use HPTuners and was told by my tuner we can but AFR should do. I have more than enough fuel pump (Squash) so its not like I'm testing the limits of the stock or ZL1 pumps otherwise I'd want to know fuel pressure. I also got a fuel pressure gauge but I don't think I've ever looked at it at WOT

Edit: My bad. I deleted the stock FPCM so I was trying to log fuel pressure according to my gauge that reads pressure from the fuel regulator.

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Old 08-31-2013, 02:24 PM   #3
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You can use SCT or HPTuners.

Injectors duty cycle IDC= RPM x IPW / 120000

RPM = engine RPM, IPW = injectors pulse width.

You have to set your scanner to log for fuel pressure, RPM and IPW for bank 1.

In SCT the fuel pressure is in KPA and the logged value you have to multiply it by 3 for the correct fuel pressure.

During WOT watch the fuel pressure dropping specially near the end of the WOT run.
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Old 08-31-2013, 09:17 PM   #4
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People talk about watch for pressure drop but know one says what that magic psi number you're looking for on N/A and Boosted. 58? 48? Whats to low.
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Old 08-31-2013, 09:22 PM   #5
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Quote:
Originally Posted by Nitroman28 View Post
People talk about watch for pressure drop but know one says what that magic psi number you're looking for on N/A and Boosted. 58? 48? Whats to low.
I thought mid 50's and up is safe. 55-50 is start watching and below 50 I think you need to upgrade.

Need a tuner to step up and answer.


I have no problem logging fuel pressure with the SCT.
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Old 08-31-2013, 10:31 PM   #6
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People talk about watch for pressure drop but know one says what that magic psi number you're looking for on N/A and Boosted. 58? 48? Whats to low.

Of course depends on every situation, but yes you want to keep FP up. Once you hit the dip into the 4x range then I would consider the upgrade and of course base that on your future goals. This does not really matter so much for boost or N/A, it's a generic comment. Fuel pressure is one of the lifelines to the motor, this is nothing to play around with.
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Old 09-01-2013, 10:06 AM   #7
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Thanks all I have an sct tuner that gets a error wen I try to use it so I am going to work with sct to get it fixed then try to data log and check my pressure
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Old 09-01-2013, 10:24 AM   #8
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Originally Posted by Matt @ FSP View Post
Of course depends on every situation, but yes you want to keep FP up. Once you hit the dip into the 4x range then I would consider the upgrade and of course base that on your future goals. This does not really matter so much for boost or N/A, it's a generic comment. Fuel pressure is one of the lifelines to the motor, this is nothing to play around with.
My motor just don't seem to be very efficient. After the maggie I put the ZL1/ADM controller in and pressure was dropping to 39-40psi. AFR was holding good but would lean out past 6000. So I bought the Livernois dual pump. FP still drops 47psi at 6000+.IDC is around 75%. I put a KB on it but it seem to have no affect on it. I finally just said the hell with it. AFR holds good thru the run.

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Old 09-01-2013, 12:56 PM   #9
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Ya my af was good through the dyno pull not sure about a full track run though...
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Old 09-01-2013, 01:15 PM   #10
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Not only fuel pressure matters. Injectors size and boost matters too. Size of injectors matters because they flow differently at the same pressure. Also boost works against your injectors. So, fuel flow depends on more than 1 factor and mainly the delta injector pressure and injector size.
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Old 09-01-2013, 03:28 PM   #11
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so I guess a question I have is if your AF reads good at WOT and through the rpm range then would you even worry about fuel pressure and duty cycle and all that
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Old 09-01-2013, 04:28 PM   #12
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Quote:
Originally Posted by Nitroman28 View Post
My motor just don't seem to be very efficient. After the maggie I put the ZL1/ADM controller in and pressure was dropping to 39-40psi. AFR was holding good but would lean out past 6000. So I bought the Livernois dual pump. FP still drops 47psi at 6000+.IDC is around 75%. I put a KB on it but it seem to have no affect on it. I finally just said the hell with it. AFR holds good thru the run.
What injectors are you using?


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Old 09-01-2013, 05:56 PM   #13
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My motor just don't seem to be very efficient. After the maggie I put the ZL1/ADM controller in and pressure was dropping to 39-40psi. AFR was holding good but would lean out past 6000. So I bought the Livernois dual pump. FP still drops 47psi at 6000+.IDC is around 75%. I put a KB on it but it seem to have no affect on it. I finally just said the hell with it. AFR holds good thru the run.
Is your tune commanding higher fuel pressure?
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Old 09-01-2013, 07:03 PM   #14
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Quote:
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People talk about watch for pressure drop but know one says what that magic psi number you're looking for on N/A and Boosted. 58? 48? Whats to low.
It's simple. Fuel pressure should be rock solid at your chosen pressure at all times.

If it fails to keep up with this, there is an issue. This is totally different than monitoring AFR's.
Anyone who says AFR's alone are sufficient are wrong. Changes in AFR can be caused by many things.
But monitoring FP can help diagnose problems in the fuel system that looking at a wideband will never do.

On a return style setup with boost referenced FPR, you would expect to see FP track intake manifold pressure at all times.

ie 60 psi base FP ( no vac ) + 20psi boost should see 80psi FP.
Obviously when there is intake vacuum at low loads, it will be less than 60psi.

If your system is a dead end or runs a fixed rail pressure, then that should stay solid pressure at all times. Unless there are some sort of closed loop controls in place that reference to intake pressure same as a basic mechanical return style.

But basically, anything that deviates from what is expected is deemed a problem.
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