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G4+ Differential Fuel Pressure Calculation

Link G4 Plus Software Tutorial

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Hi guys,

I’ve got a query on the calculation of differential fuel pressure in the G4+.

By the looks I can’t choose the calculation method, and it’s just FP-MAP + BAP.

Why however would I see a spike as per below? FP and MAP are not spiking, but my differential is.

Not seen this before so let me know if I’m having a daft moment!


Well, the fuel pressure value lags the manifold pressure value change, so therefore the differential is more positive. Zoom in on that data to see it more clearly. It's nothing to be worried about, since fueling on a closed throttle isn't critical (you may even have fuel cut on overrun).

Hi David,

Thanks for the reply, yes it is a little behind, but the lag isn't to the level that the log perceives on the spike. I wasn't so much worried as like you say, off throttle is not major, was more just trying to work out how PcLink is interpreting the information.

I've looked closer again in more detail, and it think its just that PcLink isn't the most synchronous.

Was only wanting to understand as if there is perceived ~60kpa+ spikes in the differential pressure with how the ECU is sampling the info ill just have to account for that in the FP trip so its not triggered incorrectly.

How Diff pressure is calculated will vary depending on your fuel settings but it looks like yours is using DP=FP-MGP.

The spike appears to be realistic to me but your screenshot is not great. Also, the data will never be perfectly synced and some logging settings can make that worse. For instance if you are logging some channels at different rates it will have an affect as well as logging too slow can cause aliasing effects. Is it a PC log or ECU log? what rates are they logged at?

Hi Adam,

Map is in traditional mode with channels being logged at 50Hz in the ECU


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