BMW Repair: cold start problem, salvage yard, temp gauge

Question
Josh,
I have an 84 318i that has just had the motor replaced with one with many fewer miles than the original (325,000 + on original).  Since I was not the one that put the engine in or witnessed the job I can only go by what the mechanic tells me.  I have done business with him for 15 years and have always been fair and did good work.  My question is I have a very hard time starting when the engine is cold.  I have replaced the Cold Start Valve, Thermo-Time Switch, and Engine Temperature Sensor.  I have a spare Idle Control Unit that I purchased from a reputable salvage yard thinking mine was bad.  The car runs exceptional when warmed up.  It even runs perfectly when the temp gauge moves a fraction of an inch into the warmer zone?  I am afraid I am going to burn out my starter because of the hard starting.  Sometimes it takes 10 full minutes.  Do you have any other ideas on what I can try or am doing wrong?  The one thing I am not sure about is if the ICU is getting anything from the sensors.  Thank you so much for your help.

Mark


Answer
Mark,
 This could be a few different things, causing the problem.  First I would make sure that you are getting a nice BLUE spark from the plugs.  Remove one, and lay it on the valve cover with it plugged into the plug wire.  Have someone turn the engine over, and watch for the spark.  If it is not BRIGHT BLUE, then you are loosing power in the ignition system somewhere.  Sometimes the wires breakdown and loose their ability to carry the energy to the plugs.  The coil could be bad as well, as they break down sometimes as well.

 If the spark is fine, check the fuel supply.  Maybe your injectors stop firing from time to time?  I would test them to see if they are the issue.  You can buy injector diodes that light up when the injector is firing.  They should be available at most parts stores.  

 Try this, and if both are working correctly then we will try something else,
 Josh