Wont start immediately

[BMW 5 SERIES]

My problem is that my 525 E34 wont start immediately after a 10-15 min or more run.
When I start the car for example in the morning everything is fine. No hesitations at the start up and no problems during the drive. If for example stop the car for one minute and then try to start the engine again nothing happens. But if I wait for about 10-15 min everything is back to normal. Any ideas what the problem might be?
It is really annoying to have the engine running if I want to make small stops.

Thanks

[moots]

My problem is that my 525 E34 wont start immediately after a 10-15 min or more run.
When I start the car for example in the morning everything is fine. No hesitations at the start up and no problems during the drive. If for example stop the car for one minute and then try to start the engine again nothing happens. But if I wait for about 10-15 min everything is back to normal. Any ideas what the problem might be?
It is really annoying to have the engine running if I want to make small stops.

Thanks

when you say nothing happens,meaning it doesn't crank at all?or does it crank but does not fire?

[BMW 5 SERIES]

when you say nothing happens,meaning it doesn't crank at all?or does it crank but does not fire?

No crank at all !!

[genphreak]

No crank at all !!It is likely to be a fuel pressure problem- if pressure is not sufficient it won't crank (the ecu waits until the pump brings it up to 43.5 PSI).

I believe there are several causes if it is this;

FPR
Non-return valve
Pump
Physical damage to the fuel line or tank-mounted pickupWhen was the last time you changed your fuel filter? It needs changing regularly on old cars, if you tend to leave your car empty it is really dangerous cos the air in the tank condenses every night and causes rust and clogs your filter. You should never leave it empty, and change your filter every 80,000km without fail. ON my car I do it every 40,000km since its old. When I get a look in the tank I'll decide if I go back to the standard replacement schedule. :) nick

[BMW 5 SERIES]

Thank you for your reply. I must mention that the problem occurs more often at summer time where the temperature is high.

About the fuel filter the last time I change it was less than 2000 km ago and I never leave the fuel level to go under 30lt.

Nick

[pingu]

It could also be a duff starter motor (sticky solenoid) or a combination of a duff ignition switch and old battery.

Although it might seem weird that a duff ignition switch could cause problems with hot cranking, I've had this problem on two different E34s (one a manual 525, the other an auto 540). On the 525 I assumed it was the starter motor but the starter turned out to be OK. Since (on the 540) replacing the ignition switch and battery, it cranks when hot every time.

For the both the 525 and the 540, things were worse in summer when the temperatures were higher. Cold starts were no problem, but if the engine had been running fro between 15 minutes and an hour (depending on whether summer or winter) then the car just became a huge paperweight.

[pingu]

Does the ECU have a sensor to measure the fuel pressure? Perhaps wrongly, I thought that there is no fuel pressure sensor connected to the ECU - if that is the case, how would the ECU be able to measure the fuel pressure in order inhibit cranking in the event of low fuel pressure?

[BMW 5 SERIES]

The battery is new. I change it 2 weeks ago. So I will check the starter motor and then the ignition key to see what happens
Thanks for the input

[joshua43214]

As a long shot, next time it acts up, try pushing the shifter farther up into park or pull it back into neutral. Could be a problem with the prndl switch. The ignition switch has a heavy load on it when the key is in run, they can overheat and cause a no start from excessive voltage drop.

[BillionPa]

http://www.bmwe34.net/e34main/trouble/535ihot_start.asp

[genphreak]

Does the ECU have a sensor to measure the fuel pressure? Perhaps wrongly, I thought that there is no fuel pressure sensor connected to the ECU - if that is the case, how would the ECU be able to measure the fuel pressure in order inhibit cranking in the event of low fuel pressure?That's a good question. The OBC knows fuel consumption so there must be a meaurement device, but I've never seen it. My guess is there is some sensor data coming from the fuel pump assembly...

[rob101]

That's a good question. The OBC knows fuel consumption so there must be a meaurement device, but I've never seen it. My guess is there is some sensor data coming from the fuel pump assembly...
i think it calculates that from the injector duty. pressure in the rail is not dependent on the pump pressure (because of the regulator)

[genphreak]

i think it calculates that from the injector duty. pressure in the rail is not dependent on the pump pressure (because of the regulator)Indeed... I wonder. I was told this more than once though... maybe I am wrong - as I know of no sensor... no doubt soemone will tell us when the sun makes it round the globe Rob. :) Nick

[rob101]

Indeed... I wonder. I was told this more than once though... maybe I am wrong - as I know of no sensor... no doubt soemone will tell us when the sun makes it round the globe Rob. :) Nick
i am not saying there isn't a sensor but i am quite sure they use the injector duty to calculate fuel consumption.
the pressure drop stays the same across the injectors to the manifold (this is why the reg has a vacuum line to the manifold) thus the duty of the injectors is the only thing affecting the rate at which fuel is going into the engine :p

[moots]

No crank at all !!

I had the exact same symptom as did a friend of mine.he replaced the starter
with a new one.no help.mounted an external solenoid to 'boost' the current to the existing one and i never had a reccurrence since.ditto with my friend.:)

[euaniebabs]

There is a non return valve that maintains fuel pressure just after the fuel pump in the tank. If this leaks, after a short stop, fuel pressure drops and because the engine is warm it does not initiate a 'cold' start. This means more cranking before fuel pressure restored and fuel reaches engine. There are procedures on bmwe34.net I think.

Other possibilities are weeping fuel hoses in the engine bay or an air leak.

Good luck finding the problem!

Euan


My problem is that my 525 E34 wont start immediately after a 10-15 min or more run.
When I start the car for example in the morning everything is fine. No hesitations at the start up and no problems during the drive. If for example stop the car for one minute and then try to start the engine again nothing happens. But if I wait for about 10-15 min everything is back to normal. Any ideas what the problem might be?
It is really annoying to have the engine running if I want to make small stops.

Thanks