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Practical Standalone Tuning: Setting Base Fuel Pressure

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Setting Base Fuel Pressure

03.05

00:01 Next up we're going to look at setting the base fuel pressure.
00:04 As I already mentioned, this has a big impact on the injector performance and flow as well as the injector data we need to enter into the ECU.
00:13 If you're dealing with a factory car like we are here, then there's nothing to do since the fuel pressure isn't adjustable.
00:19 The Toyota 86 we're using as an example runs a returnless fuel system which runs at a constant fixed pressure.
00:27 A conventional fuel system with a return line uses a fuel pressure regulator which is tasked with maintaining a constant pressure difference across the injector.
00:36 What this means in plain English is that as the manifold pressure drops, fuel pressure is decreased, and as manifold pressure increases, so does the fuel pressure.
00:47 The aim of the regulator is to keep the difference between the fuel pressure and the manifold pressure the same.
00:52 This means that the flow from the injector will also be constant for a given pulse width.
00:58 If you don't have the luxury of adjusting fuel pressure, then it's handy to at least know what it is.
01:04 You can find this out by measuring it or from factory data.
01:08 If you do have an adjustable regulator, we'll look now at how to set up.
01:14 Most adjustable fuel pressure regulators have a simple locking nut and an adjustable screw that can be wound in to increase fuel pressure, and out to decrease it.
01:24 There is also a vacuum port that is referenced to the intake manifold so the regulator can do its job.
01:31 Usually the regulator will also have a pressure port that can be used to connect to a fuel pressure gauge.
01:37 Adjusting the fuel pressure needs to be done with the engine running to make sure the fuel pump is receiving full charging voltage.
01:45 We also need to remove the vacuum hose from the fuel pressure regulator, and while setting the fuel pressure it's important to blank this line so the engine doesn't have a vacuum leak.
01:55 Now we need to loosen the locking nut, and then wind the adjustable screw in or out until the fuel pressure on the gauge matches our aim.
02:04 We can then carefully tighten the locking nut.
02:07 One of the most common mistakes people make is to set the fuel pressure without removing the vacuum hose.
02:14 When we're setting base fuel pressure, we need to set the pressure difference we want across the injector, and while we're doing this we need the regulator to be referenced to atmospheric pressure.
02:25 There's no hard rule on what fuel pressure you must run.
02:29 It will depend on your injectors and the size of your fuel system as well as how much power you want to support.
02:37 As a guide most conventional fuel systems with a regulator run at around three bar or 43.5 psi base pressure while most returnless systems run at around four bar or 58 psi.
02:51 So by the end of this module, you should be able to correctly set your base ignition timing, check for timing drift, and also set your base fuel pressure.