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Differential fuel pressure Vs rail pressure

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Hi guys,

Quick question here, consider the scenario of a NA car using a returnless fuel system that is fixed pressure at say 58psi. As the load on the engine changes, the differential pressure across the injector will increase over 58psi which in turn will cause the fuel flow through the injector to vary.

I am setting up a haltech elite on a vehicle and utilising the VE model but we have no solid data on the stock injectors and I am afraid changing the stock injectors isn't an option at the moment. I want to get some okish data in to my fuel flow table so that the haltech knows how the fuel flow varies with differential fuel pressure. I have access to a launch injector flow test tool that can vary the pressure to the injector and measure the resulting flow.....would it be accurate if I did this to enter into the differential pressure Vs fuel flow table?

Exactly which table(s) are you trying to adjust? Post screenshots please.

Yes you're correct, the differential pressure will increase as the engine moves into vacuum. If you don't have full data for your injector then you can calculate the theoretical change in fuel flow as pressure changes provided you have at least one reference flow value and pressure for the injectors. This formula is included in the EFI Tuning Fundamentals course but you want to take the square root of the new fuel pressure divided by your reference fuel pressure and then multiply this by your reference fuel flow. This will give you results that are close enough if you don't have full data.

Thank you for the response Andre

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