coil questions.....

[der affe]

stupid quick question....
other than the ignition switch turning on what is needed to energise my coil? i'm pretty sure it crapped out on me, it reads neg. across all terminals (using a logic probe) with the key on. with the key on the ecu should be on, but does the crank sensor (seems ok), tps (also seems ok), or anything else need to be working to get power from the coil?
also is there an "upgrade" coil? i remember seeing an e-36 coil used once, i don't remember if it was a performance upgrade or just astetics.
thanks,
greg
BTW, i don't have a bently to check the values of anything or checking proceedures so i am screwed for book help

[StereoInstaller1]

Um, Mr. Bravo, sir?

Massive Lee posted a great link to ALL of the BMW electrical diagrams.

This should help: http://wedophones.com/BMWManualsLead.htm

Luke

[der affe]

thanks, luke.
you can call me johnny bravo if you want,
at work they call me porno guy or johnny bravo

[der affe]

bump

[euroshark]

If you paypal me shipping I can send you another coil.

[StereoInstaller1]

Greg, are you not familiar with how a coil operates?

Basically, here is the deal. You will see a positive across both terminals until the motor turns over. As soon as the motor is cranking, a pulsed "ground" will happen at the same time a spark is needed.

That pulse is pretty short. Look at it like this: Engine RPM X # of cylinders / 2 (cam and distribotor spin at 1/2 engine RPM) so at 3000 RPM you will have 9000 pulses per minute on a M20. Don't expect a test light to do that quick of a flash.

If you do not have 12V at the terminals with the key on but the engine not running, you have another issue.

Luke

[mikeedler]

I am almost positive that the ecu switches off the coil wire #1(plus side) if the ecu doesnt read that the crank is spinning and picking up a sifnal from the crank position sensor.--- its a safety thing for accidents and such. so test it while you are cranking the motor.

[der affe]

i did test it while my roommate turned over the motor with my logic probe and it read neg (ground) with the key on (at both terminals, even the coil wire in the middle) and while it cranked (it still showed neg at all terminals). i didn't have my VOM at home at the time to check the actual voltage at the coil. i figured if it read neg both ways at both terminals the coil would be a gonner. been have an intermittant dying prob that i can never seem to duplicate when i am looking for it, then it finally just crapped out, so i had to find the prob and correct it. i'll bring my VOM home from work tomarrow and see what the actual voltage to and from the coil is. so am i wrong ain my assumptions?

[StereoInstaller1]

Greg, you have to see positive on one of the terminals.

I do not know if it gets voltage from a relay connected to the ECU or not, but the ECU should not run the coil directly...too much strain.

I will try and test mine today. I need to change oil anyway...

Luke

[mikeedler]

I had a similar problem last year, and it was a ground connection solder point in the engine wiring harness. it was where the grounds come together for the crank pos. sensor.- you have to cut apart the harness covering to get to it though.

[dark89e30]

The ECU does run the coil directly. It pulses the ground side (vs. positive so it does not internally short itself out, same as fuel injectors) so when the key is in the run position, there should be battery voltage on the posi side of the coil. You will not be able to measure the outgoing voltage with your DMM, you need a labscope to graph out the voltage as it goes up to 30k voltes sometimes. Do you have a DMM of just a VOM. If you can measure ohms, the primary winding resistance (neg terminal to positive terminal) should be .5 ohms and the secondary winding (posi terminal and center tower) should be 5k ohms. Replace the coil if the numbers are off by more than, say, 10%.

[der affe]

thanks, sometimes i can't see the forest for the trees. i realized this morning that.......duh if you have no + voltage to the coil, then you are not going to have anything comming out the other side, mongo dumb ass.

on a brighter notethe other replies help, since now i have to chase the prob. BEFORE the coil in the harness or CPS.
god i hate wiring!!!!
anymore suggestions or ideas where to start are welcomed!!!!
greg

[der affe]

The ECU does run the coil directly. It pulses the ground side (vs. positive so it does not internally short itself out, same as fuel injectors) so when the key is in the run position, there should be battery voltage on the posi side of the coil. You will not be able to measure the outgoing voltage with your DMM, you need a labscope to graph out the voltage as it goes up to 30k voltes sometimes. Do you have a DMM of just a VOM. If you can measure ohms, the primary winding resistance (neg terminal to positive terminal) should be .5 ohms and the secondary winding (posi terminal and center tower) should be 5k ohms. Replace the coil if the numbers are off by more than, say, 10%.

actually it is a DMM, i'll check it out, thanks!