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Old 01-20-2009, 11:07 AM   #8
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Join Date: Jan 2009
Location: South Florida
Posts: 271
My Ride: E46 330ci Turbo
Originally Posted by F1004fun View Post
I have a little trick we use at the shop, the fuel pressure regulator on the stock fuel filter is adjustable...... but only once maybe twice and only up.
The way most regulators work is they adjust the spring pressure on the backside of the diaphram sooooo. Get a bar clamp as long as the filter, your gonna use this to squeeze the regulator. Take a 16mm or so size socket and center it on the end of the regulator, on the other end take a piece of wood 2X4 and drill 2 holes in it where the two hose connections need to stick through cause you DON'T want the press on the end of the hose connections. Jig this contraption up in the car with a pressure gauge on the outlet end and fire up the pump, or you can just cycle the key to kick it on. Crank in on the bar clamp and watch the pressure rise .

I know this sounds like an accident waiting to happen but it really works and if its worth it to you I have found that with a straight through design muffler a little pressure helps, I run my 330 at 60psi. But with stock exhaust any more pressure and its wayy too rich.
What you did, raising the fuel pressure, was a complete waste of time and money. By raising the fuel pressure, you richened up the mixture. The ECU will detect this richer mixture (via the oxygen sensors during closed loop operation) and adapt to it (lambda adaption will be negative, ie, it's pulling fuel out). The net result, after lambda adaption settles, is the EXACT same fueling and mixture that you had with the stock fuel pressure regulator.
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