Cold start problems.

[Mou_Cha]

Hello guys.
I have a problem with starting my bike. On normal weather, the bike start on maybe 3th try. On cold weather i almost drain my batery on a start. After warming up is everithing good. I have done some wiring continuity chechking a i have found 4,5 kΏ resistance between EFI pin 13 (ground) and  ground of the temperature sensor connector. (temperature sensor has been disconnected). The ground of the temperature sensor connector and main ground shows the 4,5kΏ also. The continuity of the EFI pin 13 and the main ground is ok and continuity between EFI pin 10 and temperature sensor connector is ok.. I have checked the wiring diagram and the ground from the temperature sensor goes to a relay called temperature switch unit. Other diagrams shows, that it should be grounded, but i see the 4,5kΏ resistance. Can be this the problem?. I have checked the temperature sensor by measuring the resistance between pin 10 and pin 13 on the EFI connector and it was approx. 11kΏ. That is too high. 0°C should be 5kΏ. Maybe this is not the reason with the cold start, but i must start somewhere.  I have changed the fuel pump last year and after that the starting was not so fast like before, but maybe this is not the reason..

Spark plugs original from BMW dealer, battery, oil, oil filter, fuel filter, air filter. Everithing buyed last year new from official BMW servis.

[Inge K.]

The sensor doesn't ground through the fan/warning lamp relay, it's a dual element sensor......
one element is connected to the L-jetronic for calculating the mixture,
the other element is connected to fan/warning lamp relay.

The sensor grounds through the threads/gasket between the water stub and sensor,
corrosion in the threads/gasket joint is a problem now and then.
Try a to ground the sensor housing separately, to verify if this is the problem.

With a higher resistance in this circuit your bike should run much richer than normal, wet fouling?

[Mou_Cha]

Thank You for the reply!  :2thumbup:

It seems, that i have measured it wrong..
I will check that. I dont feel any problems while riding, but i have a fuel consumption approx 7-8l per 100km  (normal driving. Not like an idiot.). Maybe, that this wil be the reason. I cant check the spark plugs right now for wet fuel, but the color of the spark plugs is  more to black..  I will take out the sensor and measure it. I have a laser thermometer so i will check, if the sensor works right.

I cant do any more tests right now, but next week my bike will be ready for some more tests.

[Inge K.]

, but the color of the spark plugs is  more to black..

Another sign of a to rich mixture.

Easiest sensor test, would be to repeat the last test in the first thread...with a separate ground on the sensor housing.

[Mou_Cha]

I have tested the temperature sensor separately. Both of the resistors work fine.. :/ .. The bike is not assebmled yet, so i cant run some better tests right now. I will check the air temperature sensor also.. That could be the reason too.. I have assemled a new fuel pump. could be the fuel pressure also a problem?.

[K75RT Keith]

I may have missed this in your post but, when did you replace with new or properly cleaned and gapped sparkplugs?  When were the  fuel filter & air filter renewed?   Are you running fresh gas?   When were the injectors cleaned?  Is the crankcase breather tube cracked?  Have the TB rubber bits been checked for cracks or missing caps?  Any and all of these issues can and will affect starting. 

If I remember correctly the L-jetronic units are not real good about adjusting for temperature.  So no matter what you do, it may not be happy starting in cold weather.

[Mou_Cha]

Thank You for some new suggestions.
I didnt have gapped the sparkplugs. Sparkplugs and every filters was changed during the BMW official service. They have changed some rubber pipes, but dont know what exact pipe was changed. I will try to check this. They changed the two sparkplug cables. (measured all the cables and exept one cable all was 5kohm. Only the one older was 6kohm).
It has been done last year.

Last year i have a big problem with fuel pump turning off. While normal riding, the pump turned off. sometimes for 5 minutes, sometimes for an hour. Whenever i have tryed to done some measuremen ,the pump has runed again normal.. It was a bad wire inside the
entrance to the fuel tank. Everithing looked like a bad hal sensor, so i have changed it also (Hal sensor from K1100. The same honeywell hal sensor on the same housing. Only the connector was different) . After that i have changed the fuel pump.
After discovering the bad wire and fixing it, the bike runned fine. With the starts also. But it was a warm weather, so i cant tell if the problem with the starting starts there..


Normaly i run fresh gas. This time the gas was 2 months old. Could be also the problem i agree..