Peculiar stalling problem

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bejerana

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Kamuela, Hawaii
I'm hoping one of you can shed some light into a peculiar stalling problem I have. First of all let me explain what happens; the BMW starts first crank every morning, runs great, and I can drive it for long distances (50+ miles) no problem. The stalling happens virtually every time the engine is shut off and sits for 10-15 minutes and gets restarted while still hot. I can maybe drive half a mile and the engine stalls. When it stalls, it can take anywhere from 20 min to 2 hours before I can restart it. Once it restarts it runs again without a hitch.

I've searched on the forums but could not find any similar issue.

My car is a stock 1973 3.0CS with dual carburetors. So far I've replaced the plugs, cap, rotor, coil, fuel pump, fuel filter & all fuel lines. All replaced parts were genuine BMW. I thought it was vapor lock, so I insulted the fuel lines in the engine compartment, but it did not make a difference. Any ideas of what I should look into would be much appreciated. Aloha!
 
You have to be careful insulting those fuel lines...
When you say you replaced the fuel lines, do you mean all the lines, from the tank to the carbs?
 
Vapor lock in gas tank? Any pressure release when removing the cap after driving a while?

Is your ballast resistor and coil the right combination?
 
I am not familiar with your car so what I say may not apply. Based on owning an e24, if you car has a fuel pump relay , the symptoms would fit a bad relay. When I had a 320i, similar symptoms would happen. Apparently the copper winding in the distributor can crack (but looks fine) and periodically, the car would die instantly. I would have to wait some period of time, it varied, and then it would start and run fine. Only happened when hot.
 
Thanks for the suggestions, I will look a little further into it.

The coil shouldn't be cracked, as I just repalced it with a OEM BMW one. I also did replace all rubber fuel lines from the tank to the carbs. When I insulated the fuel lines in the engine compartment, I did so with aluminum foil and aluminum tape, seems to have been the easiest and cheapest solution. Unfortunately it made no difference. Also, there is no pressure release when I open the Gas Cap after a stall, I did try that.

I will take a closer look again at the coil as well as the carbs. I have an all mechanical fuel pump, no electronics at all, so I don't think it could be a relay.
 
Other possibilities may include a bad ignition switch (complete switch/harness) and a bad wiring connection between coil and fuse box.
 
Yep, time to check wiring integrity at the coil etc. Next time it fails check voltages at the coil.

bert35csi said:
Other possibilities may include a bad ignition switch (complete switch/harness) and a bad wiring connection between coil and fuse box.
Click to expand...
 
Get a 4' jumper wire and go drive until it does it. While it's "not starting" jump the + coil terminal directly to the + battery and see if it starts.
 
Seems possible, but I does seem to have spark at all times, as I tried to add a bit of starting fluid or gas down the carb when it wasn't starting, and it sprang to life until the gas in the carb burnt off - then died. I also unplugged one of the spark plug wires and it grounded it while my wife tried to start the car, and there was spark. So it seems a fuel delivery issue. I just can't seem to pinpoint where.
 
Screen clogged from sediment in the tank sending unit? When stalled is fuel coming out of the pump to the carbs?

bejerana said:
Seems possible, but I does seem to have spark at all times, as I tried to add a bit of starting fluid or gas down the carb when it wasn't starting, and it sprang to life until the gas in the carb burnt off - then died. I also unplugged one of the spark plug wires and it grounded it while my wife tried to start the car, and there was spark. So it seems a fuel delivery issue. I just can't seem to pinpoint where.
Click to expand...
 
The carbs seem dry, so not getting any fuel. I did check the sedimentscreen and pickup in the tank and seemed fine (nothing obstructing it). It puzzles me...
 
Did you replace the hose from the sender to the metal pipe in the trunk, and ensure a tight seal? Rules out the carbs if both are dry.

Perhaps could be a short to the idle shut off valves? Maybe next time it stalls jump the wire that goes to both to +12v.

Otherwise I guess you could disconnect the line from the pump to the tee fitting to briefly see if gas is getting there (obviously carefully aim the hose into a container with an extinguisher handy).


bejerana said:
The carbs seem dry, so not getting any fuel. I did check the sedimentscreen and pickup in the tank and seemed fine (nothing obstructing it). It puzzles me...
Click to expand...
 
Perhaps could be a short to the idle shut off valves? Maybe next time it stalls jump the wire that goes to both to +12v.


This
 
Internal fuel

pump check valve not holding allowing fuel to drain back to the tank is one possibility. Can actually drain a carb if your inlet valves are a bit leaky. A cheap fix is a marine check valve for an outboard motor.
 
Was 20 years ago but I knew I wasn't crazy. It was a crack in the wiring of the pulse generator ( number eight) in my 320i that caused the identical issue... which your car does not have.

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