E34 535i: motor misfires at acceleration

[Jazz_89]

Dear Bimmernuts,

since a few months, my E34 535i makes a stuttering sound at acceleration, as if the engine misfires and the power is suddendly reduced. I want to notice, that I only drive the car every 3-4 weeks for a few kilometers. The spark plugs where recently checked, so I assume it must be the fuel pump? I will try to jump wire the fuel relay ports this weekend to listen for the fuel pump operation at startup. Can you suggest any good tools for measuring the fuel system pressure? I could only find cheap gauges online, which do not seem very professional.
Thank you

Best wishes
Jazz

[shogun]

Besides the fuel pump working you also have to check the pressure and the flow.
The M30 fuel pump is originally Bosch 0 580 464 995
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 easiest way to test the 2 fuel pumps on my E32 750
without much work and disassembling: Open the hood, remove the cover from B+ post, use a piece of cable/wire and jumper from B+ for a brief time directly onto fuse 23 and then to 24. Ignition off when you do this. Before doing that squeeze the 2 fuel hoses coming up left hand side and do the same after you gave power to the fuses. The fuel pumps will prime for a moment then. As engine is off, one can easily hear each fuel pump when they start pumping, also the fuel hoses should then under pressure afterwards.
Check which fuse is that on your 535.
A cheap and dirty test is like this http://bmwe32.masscom.net/sean750/fu...Regulators.htm
also check the fuel pressure regulator, pull off the vacuum hose from the FPR, if fuel drops out of the vacuum hose, the FPR is defective.

[Jazz_89]

Besides the fuel pump working you also have to check the pressure and the flow.
The M30 fuel pump is originally Bosch 0 580 464 995
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 easiest way to test the 2 fuel pumps on my E32 750
without much work and disassembling: Open the hood, remove the cover from B+ post, use a piece of cable/wire and jumper from B+ for a brief time directly onto fuse 23 and then to 24. Ignition off when you do this. Before doing that squeeze the 2 fuel hoses coming up left hand side and do the same after you gave power to the fuses. The fuel pumps will prime for a moment then. As engine is off, one can easily hear each fuel pump when they start pumping, also the fuel hoses should then under pressure afterwards.
Check which fuse is that on your 535.
A cheap and dirty test is like this http://bmwe32.masscom.net/sean750/fu...Regulators.htm
also check the fuel pressure regulator, pull off the vacuum hose from the FPR, if fuel drops out of the vacuum hose, the FPR is defective.

Thanks for the advice. I began by testing the fuel pump relay socket. When the key is at position 2.Accesories, I get battery positive voltage at terminal 30 and ground at terminal 87 of the fuel pump socket. But when I bridged these two pins with a jump wire (equipped with a 15A fuse) there was no pump sound. Does the key have to be in position 3.RUN or 4.START in order to be able to complete the fuel pump circuit?

[shogun]

here it says: if you jump 87 to 30 on the car the pump should run, even I believe, with the ignition off. See if 87 is hot. If there is no power there it may just be the fuse or fuse power? The coil side is run by the DME and this is where the CPS information goes.
If you are doing this the pump should be running http://www.bimmerboard.com/forums/posts/366521/

but here is says:
the pumps won't run with a jumper between 30 and 87 because u need a jumper between 30 and 87B, ot between 30 and 87 !!!!! (87B is the middle contact at the end row)
87 and 87B are ONLY connected when the relay is inserted.
87, i believe, runs the injectors, this is why pulling the fuel pump relays and trying to start will NOT depressurize the fuel system as is mistakenly tried from time to time as the injectors will not fire

http://www.bimmerboard.com/forums/posts/1107694/

[632 Regal]

Check resistance of the spark plug boots, brown ring of death also. Check the connections to the coils and injectors for oxidation. A single misfire will shut down the system to the relative cylinders. Check intake leaks also.

[Jazz_89]

but here is says:
the pumps won't run with a jumper between 30 and 87 because u need a jumper between 30 and 87B, ot between 30 and 87 !!!!! (87B is the middle contact at the end row)
87 and 87B are ONLY connected when the relay is inserted.

this explains, why no fuel pump sound was heard. I willtry to bridge 30 and 87b next time. Will be in 4 weeks when I am home again

87, i believe, runs the injectors, this is why pulling the fuel pump relays and trying to start will NOT depressurize the fuel system as is mistakenly tried from time to time as the injectors will not fire

http://www.bimmerboard.com/forums/posts/1107694/

so I run the injectors? I hope my catalytic converter did not suffer from the rich mixture after the engine started

[Jazz_89]

Check resistance of the spark plug boots, brown ring of death also. Check the connections to the coils and injectors for oxidation. A single misfire will shut down the system to the relative cylinders. Check intake leaks also.

Last time I checked the ignition system was two years ago. I will inspect spark plugs, spark plug boots, distributor cap and will replace the HT leads I guess.
Thanks

[Bill R.]

if you haven't fixed it yet, if its not an ignition problem, look for small cracks in the rubber boots and hoses from the air flow meter to the throttle body, a vacuum leak there will cause a stutter as it leans out on acceleration.