In Reply to: Re: Warm start problems posted by Rick Robinson on March 29, 1999 at 18:51:57:
: Thanks for the reply. Was wondering what method you use to check the thermo switch. Is it a straight voltage reading? This is really the last option for me, so far a few people have come forward with the same problem, but not many with possible solutions.
You measure resistance at various temperatures across the two terminals in the thermo switch with the plug removed. At 12F you should have a reading of around 8200 - 10500 ohms. At 70F, 2300 -2700 ohms and at 180F you should have a reading of 300-360 ohms. The temperature is coolant temp. The easiest way to do it is to let the engine cool to room temp (70F) indoors somewhere and measure the resistance and them start the engine and let it warm up to operating temp which should be around 190-200F and measure the resistance which should be less than 300 ohms. As you can see the colder the engine the higher the resistance and vica versa. Good Luck.
: : My '89 E34 5spd does something similar. If it is cold it starts fine, but warm it requires 10-15 seconds of cranking all at once or two attempt to start (I don't want to overheat the starter) where it always starts on the second attempt. There is no separate cold start injector on the e34 motronic and it can't be the check valve in the fuel pump or a leaking injector as others have suggested because then it would be hard to start cold as well not having any line pressure.You should check the thermo switch in the thermostat housing as this is the temp input to the DME. Mine checked out Ok . Any insight to this problem by anyone would be appreciated. I also have the off idle stumble that others have reported and have tried all the recommended fixes to no avail .I don't know if the two are related or not.