Cold start problems -- where to start?

[johna]

My 1990 318is has been getting progressively worse to start, mainly from cold.

When attempting to start it sort of fires then stalls most first attempts. It might do the same two or three times. If I use a bit of throttle it usually starts second time. If I don't use any throttle and it starts 2nd or 3rd time it sometimes sort of stutters at very low RPM then picks up.

Also sometimes the revs go a little over 1000 rpm when it starts as I am sure they should, but sometimes it just goes to 500-700rpm.

Sometimes it does all this when warm too but mainly when cold.

So the question is what is used during a cold start? Is it just the temperature sensor and the computer adjusts things according to that or is there other parts involved just with cold starts?

Where should I look if I want to fix it myself?

Thanks.

[johna]

OK so now the problem has progressed to where the car wouldnt start for maybe 10 attempts yesterday and this morning wouldnt start at all.

This morning when it wouldnt start I pulled off the AFM and checked that it was ok as best as I could. I also swapped DME and fuel pump relays. It wasn't until I pulled off the fuel pump connector to check for voltage there that it almost started, then when i plugged it back in it did start. However this may just have been a coincidence.

To explain the problem a little better... the car cranks and then starts and dies immediately.

The Bentley manual (not really for M42) suggests that a likely cause is Motronic operates the fuel pump initially then checks engine speed sensor to see if the car has started and if not kills the fuel pump. Any ideas where the sensor is?

Surely someone has had this problem before that might be able to give me some advice?

[StreetSpec_iS]

To explain the problem a little better... the car cranks and then starts and dies immediately.?

sounds like a dying fuel pump to me.

mine was intermittent like that, then one day it wouldnt start at all (started but revved down to stall), then the next day, it started fine. drove it to the workshop, then tried to start it and it was completely dead again.

[318-is]

to start a car you need four things; fuel, spark, compression, and a cranking voltage (to create RPm of about 100)

so fisrtly, like mentioned, check your fuel pump! also, running a compression test may also be good, although the fact the car is cranking suggests your starter motor is ok. also, is the car runs as normal, compression and spark issues can also be ruled out i would think. check/replace the pump first

after that, perhaps it might be worth checking the resistances of the cam/afm/coolant temp sensors or getting it on the diagnosis?

[johna]

PLEASE HELP... Problem is still happening.

According to Bentley manual (not specifically for M42 but covers earlier Motronic system) that with a problem such as this -- engine starts then dies immediately -- that the Motronic system looks for an engine speed signal or something to check if the engine has started and if not it kills the fuel pump. This sounds like what is happening to my car.

I don't think it is the fuel pump as if I start the car with the accelerator down the engine may start and rev high for a fraction of second then die.

Any further suggestions or anyone had same fault?

[mrjezza]

as i understand it the ecu gets engine speed readings from the crank sensor.  if that dies it wouldn't receive a reading.

[M42boy]

There is a cold start procedure on this car involving the flywheel isn't there?  Extra fuel at startup?  

No cold start injector or valve like on the old CIS-E cars, but I think there's a switch/trigger to tell the computer to dump in more fuel and/or engage the starter longer.  Just an idea, although I must admit, I don't know much about it.

[318-is]

yes there is a  temperature sensor in the cylinder head (blue top) to tell the ecu the coolant temperature.

if your crank sensor has failed then your engine wont be very happy. try measuring the resitance, think mine was 90ohms last time?

[///Motorsport]

not that this is the problem, but the other day i was poking around the engine, checked the airbox, etc.  Wheni went to start teh car, it had the same symptoms, but would saty on with throttle application, die without it.  This was an easy fix, as a vaccum line had come off somehow.  I'm sure you have already, but just make sure every line and hose is snug?

[johna]

The problem may be solved now. So for the information of anyone else who may encounter a similar problem here's the story...

I took the car to my local friendly BMW specialist and asked nicely for them to check for fault codes (Australian cars don't have the check engine light so can't read fault codes without the right tool). There was no fault codes and he did a quick check that the readings were all ok.

He saw the problem (the car took about 5-10 attempts before it started there) and said that the first thing he would try would be to clean the airflow meter and the throttle butterflies.

I got some carb cleaner and did this and since then (a week ago) it has started first go every time. Hopefully it continues to do so.

So if you are having starting problems clean your airflow meter and throttle butterflies!

Incidently, prior to the cleaning I repaired all the cracks and splits in all of the vacuum hoses that I could reach with that special rubber hose repair tape (used tape as it was $10, new hoses were $200 AUS) and some cable ties, and cleaned the ICV and was amazed how much the idle improved. Didn't help the car start though.

[318-is]

glad you got it sorted mate, a lto of problems with idleing/starting seem to be vacuum hoses these days!