[Efi332] newbie (also Autronic EFI and Bosch ignition modules)

[Andrei Chichak]

 > The ignition system uses Bosch ignition 
drivers and Mitsubishi coils. I have been
 > having problems with the car eating coils.  I 
wonder if they are getting too hot. The
 > coils are mounted right to the head (they 
probably get pretty hot just from this) but
 > also I wonder if the ignition modules are working correctly.

The Bosch ignition modules will charge the coil 
then shut down after a short period of time. The 
dwell time is satisfied so it stops the current 
flow. After a little while longer it completely 
shuts down (as seen by my experiments). BUT the 
ignition module is basically just a great huge 
transistor switch that switches the coil to ground.

I'll bet that you are blowing coils because the 
coils need a ballast resistor and you don't have 
one. There are a couple of coil styles, low 
resistance and high resistance. Low resistance 
are about 0.5 Ohm on the primary and the high 
resistance ones are about 3 Ohms.

The low resistance ones are expected to either be 
run with a system that can handle them or with 
(typically) an external resistor. This coil is 
fed raw power during start then switched over to 
a 3 Ohm current limiting resistor during run.

Running without a resistor will have the coil 
drawing about 24 amps all of the time and it will 
make a big spark - for a while. Your di/dt will 
be huge compared to the normal 4 amps for the 
same period with the resistor, but you have to 
dissipate 36 times the heat if I have my math right.

With a high resistance coil you just draw 4 amps during start and running.

Andrei

 > Regards,
 > Erik Berg


------------------------------
Andrei Chichak

4024-120 Street
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