Hey guys, I understood why a pressure reg is boost referenced and that it raises the fuel pressure 1:1 with boost pressure, But I noticed on a car I was working on today at idle (high vacuume) with the boost/vac line connected it actually pulls fuel pressure down to 35psi, once you open the throttle it raises to 44psi.
So just wondering why it drops pressure under vac? would not keeping the higher pressure at idle help atomization and give a better quality idle?
Vac/boost referenced fuel pressure regulator
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Read the manual to see if your question is answered there before posting. Many users will not reply if the answer is already available in the manual.
If your question is about troubleshooting, configuration, or tuning, you MUST include your processor type (MS-I or MS-II) and code version in your post. If your question is about PCB assembly or modifications, you must also include the main board version number (1.01, 2.2 or 3.0).
If you have questions about MS1/Extra or MS2/Extra code configuration or tuning, please post them at www.msextra.com Such questions posted here will be moved to: a temporary MSextra sub-forum, where they will be removed after 7 days
The full forum rules are here: Forum Rules, be sure to read them all regularly.
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ReaperCustoms
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Re: Vac/boost referenced fuel pressure regulator
The idea of a vacuum controlled fuel pressure reg dates back to the early days of injection. It counteracts the 'suck' on the injector by reducing the fuel pressure. Hence at idle - high vacuum - you have low pressure. Wide throttle - low vacuum, so maximum pressure. These days it is likely better done by electronics.
But not sure what happens with a boosted unit. I thought it simply stayed at max pressure (same as low vacuum) under boost.
But not sure what happens with a boosted unit. I thought it simply stayed at max pressure (same as low vacuum) under boost.
Dave P, London UK.
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DonTZ125
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Re: Vac/boost referenced fuel pressure regulator
The idea is to maintain the pressure differential across the injector orifice. Since flow through an orifice varies with the square root of pressure differential (to double the flow you need 4x the pressure), it's easier on the tuner and the processor to maintain a steady pressure. Assuming a nominal 3 bar / 43.5 psi / 300 kPa differential, at idle (40kPaA MAP) the rail pressure would be 340 kPaA. At wide open on a NA engine (100 kPaA), the rail pressure is 400 kPaA. Under 140 kPa of boost (~20.3 psi), the manifold pressure is 240 kPaA, so the rail pressure would be 540 kPaA, or 78.3 psia / 65.6 psig.
