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Old 01-20-2012, 08:47 PM
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johnstern johnstern is offline
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Location: Cape Neddick, Maine
 
Join Date: Mar 2007
Posts: 843
Mein Auto: 2000 BMW 528iT/5, S/C
Quote:
Originally Posted by Steve530 View Post

So it seems likely that the nipple was indeed a vacuum source for a fuel pressure regulator. At high engine speed, a vacuum would be applied to the FPR to increase fuel flow. At idle, the high manifold pressure the closes CCV diaphragm and no vacuum would be applied to the FPR through the line connected to the nipple.
BB this thread is indeed very interesting.

I have an additional comment on the above quote from Steve530's post and that is that the vacuum for the FPF on the M52 motor and all other FPRs that I am familiar with works in exactly the opposite way that Steve530 describes.

When the engine is at idle (& at deceleration) it produces the greatest vacuum. This vacuum applied to the FPR reduces the fuel pressure at idle-less fuel is needed at idle. I know this for sure because when I installed a supercharger kit on my 2000 528iT (M52TU), I kept getting 1088 & 1089 fuel control fault codes-the short term fuel trim was in the -24 to -27 range on both banks when the engine was at idle. The instructions from the SC company had me disconnect the L shaped connector from the CVV and route it to the intake tube of the SC, sealing off the connection for that tube at the intake manifold. This removed the vacuum source from the CVV and hence from the FPR. I finally connected the vacuum hose from the FPR to an unused 3.5mm vacuum nipple on the back of the intake manifold-the STFT values went to -2 to -3.5 (normal) and no more fuel control fault codes. So the vacuum reduced the fuel pressure at idle. Also when the throttle is opened the vacuum is decreased & fuel pressure is increased when engine power needs to be increased.

BTW your vacuum port #9 above with the cracked cap is connected, in my car, to a vacuum line that supplies vacuum to the brake booster. Also the FPR in the M52 (single Vanos) is located on the fuel rail. On the M52TU it is relocated under the car, just in front of the fuel filter, under the driver's seat. On the M54 the FPR is integrated into the fuel filter located under the car, under the driver's seat.

Last edited by johnstern; 01-20-2012 at 09:04 PM.
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