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Peter I am not sure if the two issues.......... (archive)
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Posted by Grant on February 24, 2002 at 17:45:59:

In Reply to: 733i loss of residual fuel pressure posted by Peter Barnett on February 24, 2002 at 13:06:38:


She (83)experiences a stutter or shudder between 2 and 3k RPM. I have checked and replaced numerous components without success. Recently I checked the fuel pressure and it holds steady at at 30 psi when running, but it almost immediately falls to 0 when shut down. I am wondering if they are related? Before I start replacing components of the injection system does anyone have any suggestions on where to go from here?

are related but 30 psi seems low. I do not know the spec for your year car but one would think you should at least see 36 psi. But if the pressure falls to zero upon shutdown then I would suspect the primary fuel pump. That pump has a check valve in it to hold pressure for some time after shut down. At least for 1-2 hours you should have some pressure in the line.

When was the last time the pump was replaced? And what is the status of the pump in the tank? When was the filter changed?

Another suspect is the fuel pressure regulator. This device could be causing the low pressure. But before you blame the regulator check to see what the fuel pressure is when you remove the vacuum hose from the regulator. Pressure should rise to around 40 psi.

Find a vacuum gauge and see what the vacuum reading is on the hose to the regulator at idle and then at 2000 PRMs.

And then pinch (be careful not to damage the hose) the fuel line hose below the fuel regulator and watch the fuel pressure gauge. Pressure should spike to 80-90 psi. If so the pump is producing pressure. But if the pressure falls to zero after shut down then the check valve is not working.

Grant 1985 735i 5 speed

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