Cold Start Problems - BMW Forum

318 al · 11-29-2004, 05:43 PM

Firstly great site. I've just bought myself a 1995 318 is auto and am having a little trouble. When the engine is cold it won't rev past 2500 rpm. The revs will just keep bouncing of the 2500 mark until the car warms up. However as the car warms up the amount of revs incrases until at running temperature then all runs ok. Any ideas as this is getting to be a real problem especially with winter setting in.

Cheers Al

97alpineM3 · 11-29-2004, 07:54 PM

Honestly... I've never heard of that... I will make a few phone calls and find out..

(I know the newer cars have built in software that limits the rpms while it warms up.. but not on a older car)

If you cant find the solution.... warm the car up a head of time..

Good Luck.. and get back to us when and if you find the solution.

Les

318 al · 11-30-2004, 04:35 AM

Cheers mate. Definately need to get it sorted, very cold this morning and the car wouldn't rev past 1000rpm. I've been told its probably one of the sensors but i need to find out which one. Worse case senario will be a diagnostic check I suppose.

OutOnBail · 11-30-2004, 09:22 AM

Hi there, I'm doing research on ICE (internal combustion engine), especially the BMW's and am trying to help as i can. As the RPM of the car depends on the work done by the piston, technically the piston efficiency is encreased proportional to the temperature inside the combustion chamber. Technically it sounds like, increase temperature increases pressure in the combustion engine so the piston works more effective.

So my recommendation is...when the weather is cold, try to warm up ur car by turn on the Air conditioner (NOT HEATER)...this will help u solve the problem... The more hardcore ur airconditioner, the faster ur car get warmer and it will gives more efficiency. u can apply this technique to warm up ur car "faster" rather than waiting 2-3 minutes.

See how it goes and email me the result to 02035362@uts.edu.au

Regards,
Hendra.

97alpineM3 · 11-30-2004, 10:21 AM

Are you speaking of temperature at the moment of combustion... or of the air that mixes with the fuel?....

The colder the air that mixes with the fuel.. the more efficient the engine will run.. due to the amount of air molecules per square inch of air.. due to the temperature. Air is more combustable at lower temps... thus the mixture of fuel is more combustable and more efficient.

Which do you speak of?

Les

Aether · 11-30-2004, 10:34 AM

Quote:

Originally posted by OutOnBail@Nov 30 2004, 09:22 AM
Hi there, I'm doing research on ICE (internal combustion engine), especially the BMW's and am trying to help as i can. As the RPM of the car depends on the work done by the piston, technically the piston efficiency is encreased proportional to the temperature inside the combustion chamber. Technically it sounds like, increase temperature increases pressure in the combustion engine so the piston works more effective.

So my recommendation is...when the weather is cold, try to warm up ur car by turn on the Air conditioner (NOT HEATER)...this will help u solve the problem... The more hardcore ur airconditioner, the faster ur car get warmer and it will gives more efficiency. u can apply this technique to warm up ur car "faster" rather than waiting 2-3 minutes.

[snapback]240117[/snapback]

Warmer air is a lot less dense than cold air, so you can't fit as much into the combustion chamber, thus a richer mixture with more deposits, and poor efficiency. Turning on your air conditioner is basically the same to your motor as holding your foot lightly on the gas - you're only making it work a little harder when you engage the compressor pulley.

Just let it sit for a few minutes to warm up. Revving or stressing your motor before it reaches normal operating temperature will only harm it in the long run.

318 al · 11-30-2004, 10:53 AM

I never race any of my cars until at operating temperature, but this is rediculous. I can barely drive the car for half a mile until warm enough to allow the engine to rev.

OutOnBail · 11-30-2004, 10:24 PM

The combustion chamber has heat exchanger just outside the piston shell to avoid overheat... Yeah right, if air is colder, it is more compressible...but im not talking about the surrounding temperature around the combustion chamber... and Im trying to increase the temperature inside the combustion chamber by playing around with the heat exchanger...

If u turn on ur Airconditioner, the colder it is, the hotter the WATER in the heat exchanger so when it flows to the combustion shell to take the heat out, it is not that efficient.. this means ur combustion chamber is warmer... efficiency of the piston work is not really depending on the intake air temperature, but it depends on the compression ratio... If too hot, it is bad, but if too cold, it is not good too... Factory has their own compression ratio set up...

(T2 / T1) = (P2 / P1)^[(k-1) / k)

where k is 1.4
T2 is temp when air is compressed in the mixig chamber
T1 is temp when in the combustion chamber once piston has done the work.

Sorry sounds too theoryyy but u can try it... start ur engine and turns on ur Air Cond.. see the different...

O yeah i apologise that i forget to say that once the temperature reading hits the constant temperature reading, TURN OFF ur air cond or simply set it back to normal... and there u go...

Yeah yeah when the air cond is on, the motor does heavier work... but then this is only the starting...that`s true when u turn on ur aircond, the RPM drop but TEMP increases that`s why when u r ready to go, set back to normal ur aircond... or just turn off if outsie air is cold enough...

Extra tips... u can reverse this technique too. When ur car temp is soo hot and and ur car stop working....usually a newbie dumb may try to open up the radiator cap and feel in the water... PLEASE DON't DO this.... wait??? not a good idea!
What u can do is turn on ur HEATER and see the temp drop...once it is safe enough...refill the water....

318 al · 12-01-2004, 11:24 AM

I appreciate the help and advice and these are helpful temperary measures but, I want to solve the problem not go around it. The car didn't come out of the factory like this its clearly a fault. Therefore I would like to fix it.

Cheers Al

OutOnBail · 12-01-2004, 10:06 PM

o yeah it might also be positive when ur coolant is frozen in the pathway...check it out

einstine98 · 12-12-2004, 06:39 AM

I have exactly the same problem! Took it for repair in a well known shop, but they just couldn't figure out what was wrong! they suggested the coolant Temp. Sensor... but I'm not sure!

Any ideas!

My car is 320i 1994 model

einstine98 · 12-12-2004, 06:40 AM

Quote:

Originally posted by einstine98@Dec 12 2004, 04:39 PM
I have exactly the same problem! Took it for repair in a well known shop, but they just couldn't figure out what was wrong! they suggested the coolant Temp. Sensor... but I'm not sure!

Any ideas!

My car is 320i 1994 model

[snapback]248462[/snapback]

One more thing, I live in a VERY hot country, and it is not realted to outside temprature! I can guarantee that

meangreen94z · 12-12-2004, 01:33 PM

Actually when your engine is cold(such as right after a cold startup), because the air entering is cooler, and the temperature of the internal metals are cool, the fuel doesnt vaporize as it should and can condense on the cool intake manifold runners, and cylinder walls. This can cause a hard start condition(due to it being hard for a spark to ignite a flame across a lean air/fuel mixture), to alleviate this manufacturers either use an extra injector usually at the back of the intake manifold, or as in most modern cars widen the injector pulse width at startup. This provides the additional fuel needed(a richer A/F ratio is easier for a flame to jump across), as well as helps warm the engine up.

Turning on the A/C just places a load on the engine increasing cylinder temperatures, really you can see the same affect by leaving the car in a low gear at a higher RPM for the first few minutes of driving.