E34 540i acceleration sputter 20-30 mph

[jingo]

Seems the old girl is running into issues with acceleration.
Symptom: During acceleration from a complete stop the car will shudder a bit and possibly jerk. Feels like it's not getting enough gas during acceleration.

I've replaced the plugs. O2 sensors were replaced not too long ago, fuel filter was replaced. Checked for vacuum leaks, didn't find any but did find a vacuum plug on the back on the intake manifold was cracked, replaced that. Each time I think it's fixed I drive it a little longer and the issue creeps up again. Seems that the car has to warm up sometimes for the issue to present itself.

Thoughts/suggestions? Not 100% confident I ruled out any vacuum leak so any tips/guides would be helpful.

[Tiger]

Fuel pump

[jingo]

Fuel pump

Had replaced that darn fuel pump 4 yrs back. It did run better after I replaced the filter. Would think it'd last longer than that. Argh.

[Tiger]

Depends on what brand of fuel pump you put in...

[jingo]

Depends on what brand of fuel pump you put in...

It was an airtex brand. I actually have the old fuel pump that it replaced because I thought the fuel pump went out when it really was the crankshaft positioning sensor. Going to put the old pump back in on Friday. I'll post results!

Thanks!

[Tiger]

Cool! Cost you nothing to swap it out.

[Bo525i]

Never mind, gotta learn to read everything..

[jingo]

Swapped out this morning. Definitely bigger punch on acceleration. Will have to test it out over the weekend to truly tell. Eventually will get a oem one from rmeuropean when this one dies. ^_^ Onward to the next issue heater core o-rings. Right o passage.

[shogun]

you are on the right track. Other possibilities could be fuel pressure regulator. Pull the vacuum hose off and see if fuel is inside.
The M60 engine needs 3.5 bar!, others like the M30 need only 3.0 bar.
And the fuel pump you can test, I presently only have data on the M30 and M70 fuel pumps, but this will give you an idea:

Usually a fuel pump delivers much more fuel than the engine needs, for that is the fuel return line back to the tank. And there us a fuel pressure regulator for each pump which regulates that.
Nominal data:

The M30 fuel pump is originally Bosch 0580464995
operating pressure is 3 bar
conveying capcity at 12 V 1.9 liter/minute
conveying capacity against counterpressure 875 ccm/30 seconds
Power consumption is 5A
The M70 has 2 pumps, so 1 for 6 cylinders, each:
Bosch part number is 0580112507 (according to an old repair book)
operating pressure is 3 bar
conveying capacity at 12 V 1.7 liter/minute = less than the M30 pump capacity against counterpressure 875 cc/30 seconds
power consumption 5.5A


Testing
Fuel system -- replacing the fuel pressure regulators (v12) (http://bmwe32.masscom.net/sean750/fuel_pressure_regulators/FuelPressureRegulators.htm)

[Tiger]

Congrats! Keep us posted on your test.