engine dims to stop after a warm start

[grave77]

2 weeks ago the engine started these symptoms, in the morning it starts normally, but after a short trip, when I stop for something and return to start it, it starts for a second and the RPM dims and engine stops.

if I keep my foot on the accelerator a little it stays on.

I still have bad DK-motors, is that due to this, or I have a bad regulator valve too?

Thanks

[shogun]

Could be (but not sure) the DK motors. Maybe you first clean them and test again. Info on my website below. Done in 1-2 hours.
Or the fuel pressure is too low or fuel runs back into the tank due to a bad check valve. Engine room hot = air/fuel bubbles could build up
http://www.bmwe34.net/e34main/trouble/535ihot_start.asp

Try: switch ignition on, but do not start the engine, wait 5 seconds. Switch ignition off, same procedure, then start engine.
On the E32 fuel pumps start running with ignition on till required fuel pressure is reached, then they switch off.
If that helps, check valve in tank.

[grave77]

well would that explain the fuel smell when car is hot? I actually smell the fuel more in summer than winter especially if the car is parking while engine is on.

[shogun]

well would that explain the fuel smell when car is hot? I actually smell the fuel more in summer than winter especially if the car is parking while engine is on.

If it is the check valve, then the fuel would run back into the fuel tank, so no smell.
But check the return line of the fuel via the charcoal filter, maybe that lines are brittle and broken.
ACTIVATED CARBON CONTAINER/FUEL VENTILATION
I just took this drawing as example

http://www.realoem.com/bmw/showparts...65&hg=16&fg=10

[grave77]

latest news about this problem, I have removed the DK throttles and cleaned them as per the instructions earlier posted, the brushes were stuck cuz of carbon build up. the reason I started there is that the car was hesitating when cruising at 80 and above, sometimes miss firing, I'm starting to suspect the fuel pump, as if I'm cruising at 80 it feels like I'm stepping on the accelerator and then leave it and so on.
any advice guys?
Thanks

[shogun]

Best would be you ask your shop to make a fuel pressure and volume test. Is quickly done.
Or the DIY way, as shown on Johan's website.
Fuel pump data are in the Bentley repair manual.
Must be 3 bar, close to 2 litres/minute. But better check the manual.
Can use the one from the E32 750. Same pumps.

Actually I just ordered from www.autohausaz.com today 10 fuel pumps for 750/850 for stock for me and our club members. They have a discount at the moment on Bosch fuel pumps. Also checked the price with my BMW parts guy in Germany, but Autohaus was abt. 30 % cheaper, here in Japan they cost 3 x times the price of Autohaus Arizona.

[grave77]

hi, may you tell me if the check valve is the one they called return valve?
also may you explain me a little about the fuel ventilation system.
I was wondering if the fuel pressure would go low cuz of the old pumps or old filters more?

Thanks mate

[shogun]

Check valve sits next to the fuel pumps and blocks the return of the fuel when engine is switched off. So it has no effect when defective while driving. It is however responsible for a bad start problem. See my website the link to Bruno E34, hot start problem.

Sometimes misfiring at cruising can be a complete different problem, such as bad wheel speed sensors.
See my website under
Advanced BMW ABS hints and tips

[grave77]

" ENGINE APPEARS TO MISFIRE OR STUMBLE INTERMITINTLY
SOLUTION: Replace the ASC control unit. no further diagnosis of the ABS/ASC system should be necessary."

This is excactly whats going on with me, how and where is this unit? how much would it cost?

my rear wheels are slightly larger diameter than the oem, would that be the cause? the size now is 265,45, 17 it should be 265 40 17

[shogun]

Could be tires, but also other things as I said before. If that different tire size or a non OEM wheel does not allow the wheel speed sensors to get proper signals, you have faults, very easy.

Where is this unit? I do not know in your car, but it is for sure mentioned under component locations or fuse box/relais box details here in the right one for your year and production
http://shark.armchair.mb.ca/~dave/BMW/e31/
check it out.
Component locations shows all parts with pic and location.

How much it costs: see realoem.

I would not buy a new one, as too expensive. Get a used one after you checked the part numbers of BMW and Bosch on your car's module.