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Discussion and questions related to the course EFI Tuning Fundamentals
What is the advantage of a fuel pressure sensor setup vs a map referenced fuel pressure setup?
I am currently running a MAP Referenced setup on my Link G4+ pnp for my 3SGTE engine. I actually have a fuel pressure sensor installed and figured why shouldn't I switch to a FP Sensor fuel mode. I know the MAP referenced setup will always use the base fuel pressure entered as the differential pressure which assumes the FPR reacts immediately to changes in MGP and is 100% consistent in regulating the fuel pressure. By switching to FP Sensor mode the ECU will be able to measure the actual fuel pressure to account for any lag or inconsistency from the FPR and so should be better and provide a (slightly) more accurate fueling?
Is my understanding correct and are there any other advantages and disadvantages going from a MAP references setup to a FP sensor setup? My only worry would be the FP failing but if I put in a fail safe to shut down the engine when the differential pressure is different to base pressure, that should protect the engine?
One more question. I noted the base fuel pressure in the fuel setup setting was set to 300 kPa while in fact the real base pressure maintained by the FPR is actually 270kPa so I'll need to scale the whole main fuel table down when switching to FP sensor fuel mode. I am using VE for my fuel table, is it just as simple as multiplying everything by 0.9 (being 270 divided by 300) or there are other settings to be changed?
Other advantage I can think of is if using a adjustable FPR, I can make minor changes to the base fuel pressure on the fly (no idea why I need that) without needing to up or if the pump is just maintaining marginally enough pressure at maximum load (not a good thing), the ECU may compensate by adding more pulse width.
Are there any disadvantages though? Other than an additional sensor is needed which means there is one more component to fail?
Sensor lag maybe? I have no idea how fast these sensors react.
Your understanding is correct - Rather than the ECU assuming the differential fuel pressure across the injector it can actually measure this. The result is a more realistic VE table as you're not fudging the numbers to account for minor variations in fuel pressure.
If you're using a fuel pressure sensor and you change the base fuel pressure then you shouldn't need to adjust the VE table at all (and in my experience this actually does work out to be the case). In your situation where you've provided reference flow data with a base pressure of 300 kPa and the actual fuel pressure has been 270 kPa then yes, you'll need to make some small changes initially to the VE table to account for this small error.
If the sensor does go into fault then it can be a problem since the fuel pressure will jump to the default value. This will have some effect on your final fuel delivery but if you set this for example to a default value of 300 kPa on a turbocharged engine you'll actually end up running richer under boost which is safe, since the ECU will see a lower differential fuel pressure and hence increase the injector pulse width.
Thank you for the detailed explaination and affirmation Andre.
I'll be making a switch to FP Sensor and see how it goes. As a start before I test and fine tune the map, does multiplying everything across the board in the main fuel table by 0.9 makes sense given my actual fuel pressure is currently 90% of what the ECU assumes under MAP referenced mode, or should I keep it as is and tune everything from the current values and updating as I run through each cell.