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TnF

Differential fuel pressure - Nominal fluctuation range?

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Hello. If you remember i added a fuel pressure sensor recently and i am running differential fuel pressure compensation on the injectors. Under WOT conditions you can see that fuel pressure starts falling from about 46-48psi base fuel pressure to 40psi and even spikes up to 52psi during the gear change. Injectors are ID 1050X, 8mm fuel lines, new fuel filter, oem fuel rail (ca18det), and adjustable fpr (unknown brand, very similar to SARD design - not the copy one though, this one is riveted). Fuel pump is Walbro 255lph HP version running on the stock nissan wiring (15A fused - stock is 10A - heard there is a measurable voltage drop in our cars).

What i am wondering is this 12psi fluctuation range typical of what do you normally see, should i be worried, or is there any point of limitation in the fuel system? From the data you can see fuel flow at fuel load is 2L/min=120lph, this pump can do this flow at 90psi @12V, whereas the fuel pressure i have is much less.

I am thinking the adjustable fuel pressure regulator is the "issue", too small, with too small diaphragm.

What are your thoughts?

fuel pressure link.png

Edited by TnF

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I see just over 5 KPA pressure drop as an example.  I find the pressure slope of the turbosmart 1200 to be very good, that's what I use. 

 

I would try a better quality fuel pressure regulator and rewire the fuel pump using a realy close to the pump with large gauge wiring.

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Well i am thinking the same - it is either one of the 2..my idea is to datalog the voltage at the fuel pump to see if i have a noticeable drop - both could be an issue in the end though

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Just an update to this, the solution was to move to a more flowing FPR, i used Turbosmart FPR 800 to have a stable +-1psi fuel pressure. The issue is with a restrictive FPR all the flow from the pump increases head pressure so the base fuel pressure you set is higher than when you have less fuel returning. Either way best to use a fuel pressure sensor as i have now as well and have the ecu compensate (assuming you have injector flow data for each voltage and pressure) :)

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For the price of a decent FPR, a Fuel Pump Speed Controller is something I'm considering.  No need to upgrade the FPR or fuel return line, and keeps the fuel cooler.  

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6 hours ago, GregM said:

For the price of a decent FPR, a Fuel Pump Speed Controller is something I'm considering.  No need to upgrade the FPR or fuel return line, and keeps the fuel cooler.  

I actually went from aeromotive fpr to stock when i started pwm'ing my pump.

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