535 hard time starting on cold mornings

[DABLACK]

Im sure a few of us have run into this problem. Hard to start when cold out.starts fine when engine is warm. Any suggestions please

[shogun]

http://www.bimmernut.com/forum/showthread.php?t=40658

[Jeff N.]

Ya think? I'd say check your engine temp sensor (the blue topped one IIR). Sounds like his car is never kicking in the cold run cycle.

Try the stomp test and see if you have any codes as a start.

[factus6]

I have had this problem since I bought the car in 1999, I have replaced just about everything, even swapped the ECU and have never been able to figure this out. However I live in Austin Texas and it is usually above 70 degrees which seems to be the cut-off point 69 degrees over night and it takes a couple of cranks to start. I gave up a while back I know it will start and the starter is bullet proof so... I just don't care anymore.

[factus6]

But I am going to check out the check valve mentioned here:
Well the poor old 535 and her

[genphreak]

Temp sensors are cheap and easy to test, source and change. The output is measurable by the resistance change, and a simple multimeter will tell you if it is correct for the temperature of the coolant in the water-neck. To check the stepping of the sensor over conditions, pop it in the fridge in a 1/3 of a glass of water with a thermometer for an hour or so. Then measure it using the multimeter as it slowly comes up to ambient to see the output is smooth.

Even if it is easier for you to change it, this will at least tell you if it is the problem- something that is vital when solving intermittent running problems.

Re the fuel check-valve- this manifests no-start symptoms in hot conditions, not cold AFAIK. Another solution for this is to change the fuel pump- a lot more expensive I know, and harder to do, but if yours is old its not a bad prevenetative measure (and includes a new check-valve inside). I've used the TRE Performance pumps with great results, at low cost.

[shogun]

bad fuel check valves is cold and hot start problem.
In case of hot start problem with bad check valve inside engine room there will be a build up of gasoline vapour(bubbles) inside the fuel lines due to the heat and not enough pressure inside the fuel hoses, and in case of cold start problem the fuel just returns to the fuel tank out of the pressure lines between tank and fuel pressure regulator in engine room.
Not enough fuel pressure = cranking, cranking, cranking, till enough pressure has been built up again

as Bill R. said in his original post:

When hot, the fuel will boil in the fuel rail by the injectors creating an air lock or vapor lock when you have it under pressure it raises the boiling point and also gives it no place to go. On a cold start the fuel is denser and the pump fairly rapidly gets to the injectors , but it still starts faster with a good check valve.

[genphreak]

Ahh... interesting! Yet to see one like this myself.

I imagine the intermittent nature of the problem comes from whether the valve is behaving the same way each time one starts- and/or and how long the car has been left to stand int terms of the returned fuel vs vapour lock.

In the cold start case though I can't work out how what Bill says can happen, as when the fuel returns down the line a vacuum would be generated as it moves back as this would, of course, act to draw more fuel up from the tank.

[factus6]

I can't believe it, it was the coolant temperature sensor, I could have sworn that Terry Sayther checked that. A $20 dollar part that was so easy to install, I did not even test it I just replaced and what a difference it makes now that the ECU is getting good data. It not only starts up right away, it run smooth, in fact the car has never ran better. I also replaced the fuel pump, it did not need it but since the car is 20 years old I figured it was a good investment and TRE Performance only charged $89 and that was an easy install as well. Thanks to genphreak and shogun, you just made the car I love drive even better.

[shogun]

congrats to the new BMW drive feel.
yep, fuel pump after 20 years of hard work has to be retired.
Did you make any pics about the installation of the Tre Performance pump in your car?
Or which model did you order?
Basically their pumps are all same, just the accessories are different depending on car model.