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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old Yesterday, 07:52 PM   #1
Registered User
Join Date: Feb 2016
Location: jacksonville, florida
Posts: 4
My Ride: 1999 323I
low fuel pressure, running rough

I have a 99 323i that has started giving me problems. when i first start it up, it idles very erratically and shuts off. i have to start it several times before it will idle smoothly and let me pull off and drive. while driving after it gets going, if i floor it, it falls flat on its face. if i back off the throttle a little, it takes off like it is supposed to. i changed the plugs last week and the old plugs were black and smelled like raw gas. i first thought it was running very rich and possibly the o2 sensors have failed. a friend who is a general mechanic said it seemed to actually be starving for fuel and told me to check the fuel pressure regulator and that if it was not providing enough pressure it could not be providing enough pressure to the injectors to atomize the fuel enough and that could be why the plugs were "soaked". from what i found online the pressure should be between 55-60 psi and slightly lower when the key is turned to ON to prime the pump. my prime pressure is 25 psi and running pressure never got over 30 psi. could that low of a psi be causing the fuel to not atomize correctly and soak the plugs? if so, what is more apt to fail, the regulator or just a plugged filter? if it helps, there is no check engine light on, and when i scanned it with a generic scanner, all i got were several generic P codes, most notably first and second bank were throwing a couple of codes. unfortunately i do not have the money to pay a bmw or foreign car shop to scan it as i am helping pay for my moms chemo treatment co pays, so any help will be greatly appreciated.
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Old Yesterday, 08:12 PM   #2
Registered User
Join Date: Nov 2009
Location: Fairfax, VA USA
Posts: 18,850
My Ride: 330CiC, M5, X5
Fuel pump is the primary culprit on these cars.

Assuming the fuel pressure gauge is working and connected properly, the fuel pressure should be higher. Additionally a fuel volume test should yield about 1.12 Liter per 30 seconds.

But also make sure there are no vacuum leaks as well.
Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old Yesterday, 08:32 PM   #3
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Join Date: Mar 2013
Location: Wisconsin
Posts: 1,314
My Ride: 03 325xi 98 328is
Like jfoj said, most likely the fuel pump, an easy diy with basic tools. Easily accessed from the back seat, just don't go cheap, check FCP Euro for a real lifetime warrantied pump and fuel filter.
Hers His
2003 325xi StahlGrau metalic almost modless, just lots of new parts, wife's DD. 1998 328is lowered, X-brace, Sparco strut brace, HIDs, AEs, almost everything blacked out, my DD.
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Old Today, 08:56 AM   #4
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Join Date: Jul 2008
Location: USA
Posts: 4,619
My Ride: 2001 330Ci
The pressure has to be at least 45psi. There's a test valve on the fuel rail. Item #2 in the link is the cap for the test valve.


Your fuel pump is soft failing. It can't consistently produce enough fuel pressure. As a result it can't produce enough fuel flow. Replace:
- fuel pump (Siemens/VDO from bmaparts
- filter (Mahle or Keyser)
- 3 short pieces of fuel hose at the filter
- 6 worm clamps at the filter
- pump relay (Bosch)
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Old Today, 05:19 PM   #5
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Join Date: Feb 2016
Location: jacksonville, florida
Posts: 4
My Ride: 1999 323I
thanks everyone! i have a pump, filter and relay on the way . i appreciate all the help!
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