Another no-spark issue

[dirtrider]

43 minutes ago, jermaine_rider said:

Got ya. I need to have more definitive procedure because I am not looking forward to spending any more money at this time but if I have to I guess I have to.

Afternoon jermaine_rider

 

There are 2 ways I go on the old BMW oilhead sparking system. 

 

Test the HES, test the coil, make sure the ignition system has 12v & grounds to all places it needs to then IF still no spark look into at the possibility of a bad Motronic. 

 

Or, #2 verify power & grounds & verify a good HES then pop in a known good Motronic as a quick test. 

[jermaine_rider]

Yessir. After all is said n done, thats where I have found myself. Coil then the motronic. After that Facebook marketplace.

[MarkAZ]

Been following this...

 

Can't contribute much regarding the no spark issue but on all the ohm meters I've used, the ohm adjust was to zero the meter. You touch the probes together and adjust it to show zero ohms then do your measurement. Without the probes touching you should show infinity or some other indication that it's an open circuit, very different that zero ohms. The adjust is not to calibrate the meter, it's to offset any resistance in the probes & leads.

 

Also, using a speaker coil to test an ohm meter can be very misleading. A 4 or 8 or whatever value means impedance, not resistance...they're different animals atho they use the same unit...ohms, I won't get into the details of how they differ.

 

Not meaning to be pedantic but there seems to be some misunderstanding here that might explain some of the confusing results. Hope it helps.

[jermaine_rider]

Hey thanks for the advise on the ohm meter MarkAZ I thought I was doing something scientific. Anyways, today, my new to me coil arrived and before doing anything I wanted to satisfy my curiosity on whether my multimeter was reading the primary correctly or if the coil was indeed bad. So just like before, I put the probes to the primary and got zero reading. That, almost solidified my desire to push this bike into the Hillsborough river and be done with it. But before I do, i'm going to trade this coil in for a used motronic and that, if it doesn't work, will be the straw that broke the camel's back that made him push the bike into the river. I mean, after all this, and the coil I replace my other one with is reading the same thing basically telling me that either I'm doing something wrong or my meter is not functioning correctly, there's no other place to turn but the motronic correct? Fuses are good. No wires need replaced. Everything is grounded and everything else is working fine. But still no spark.

[dirtrider]

12 minutes ago, jermaine_rider said:

Hey thanks for the advise on the ohm meter MarkAZ I thought I was doing something scientific. Anyways, today, my new to me coil arrived and before doing anything I wanted to satisfy my curiosity on whether my multimeter was reading the primary correctly or if the coil was indeed bad. So just like before, I put the probes to the primary and got zero reading. That, almost solidified my desire to push this bike into the Hillsborough river and be done with it. But before I do, i'm going to trade this coil in for a used motronic and that, if it doesn't work, will be the straw that broke the camel's back that made him push the bike into the river. I mean, after all this, and the coil I replace my other one with is reading the same thing basically telling me that either I'm doing something wrong or my meter is not functioning correctly, there's no other place to turn but the motronic correct? Fuses are good. No wires need replaced. Everything is grounded and everything else is working fine. But still no spark.

Afternoon jermaine_rider

 

Try the new coil, if that doesn't help then suspect he Motronic or the HES.  

 

Did you try the test light across the coil 12v supply & trigger wire to see if the test light flashes while cranking? If it flashes while cranking then the Motronic is probably OK, if it doesn't then the test light might not be able to flash fast enough, or the HES or the Motronic might be bad.  

 

Basically if it flashes that will tell you something positive if it doesn't then you will need to dig in deeper.  

[jermaine_rider]

What is this trigger that you speak of? I get power from the green wire with key on and while cranking but haven't noticed if it was blinking or not.

[dirtrider]

4 minutes ago, jermaine_rider said:

What is this trigger that you speak of? I get power from the green wire with key on and while cranking but haven't noticed if it was blinking or not.

Afternoon jermaine_rider

 

Unplug the connector with the green & black wire from the coil then put a 12v test light across the green wire & black wire, then crank the engine. See if the 12v test light flashes.  

[jermaine_rider]

If anyone is still tuning in, I have isolated the problem, I just dont know what to do about it. I appears that the trigger wire going to the coil is not receiving the signal from the motronic. Now I need to figure out if there is a break or fault in the wire, or a motronic issue. My question is has anyone heard of this happening, where the motronic is not sending the signal? Or should I just go ahead and start following the wire til I find the issue? That wire does run straight from the motronic to the coil is that correct? Thanks again for all the help.

[jermaine_rider]

Well I broke open the motronic. I see a resistor that looks like it is fried. Gonna try to fix it. Got nothin to lose at this point. My life is a never ending battle for serenity. Ill get there one day, dead or alive.

[dirtrider]

7 hours ago, jermaine_rider said:

If anyone is still tuning in, I have isolated the problem, I just dont know what to do about it. I appears that the trigger wire going to the coil is not receiving the signal from the motronic. Now I need to figure out if there is a break or fault in the wire, or a motronic issue. My question is has anyone heard of this happening, where the motronic is not sending the signal? Or should I just go ahead and start following the wire til I find the issue? That wire does run straight from the motronic to the coil is that correct? Thanks again for all the help.

Morning jermaine_rider

 

Yes, that is pretty well a direct run but that wire is usually a shielded circuit. 

 

The Motronic doesn't actually send anything it simply drives the coil's low side (black wire) of the coil's primary from low to high (basically grounds then ungrounds it) to force primary collapse, then that produces a high voltage (ie spark)  on the secondary side. 

 

I have seen (and heard of) failed Motronics, usually after some sort other electrical issue like a shorted HES or output circuit overload. 

 

Are you getting both full time 12v & ignition switch ON 12v into the Motronic?  If it isn't powering up properly it can't work properly. 

[jermaine_rider]

It appears that there is a fried resistor in the motronic. I'm gonna try and fix it. Rather  give that a shot first since that is where the problem seems to be emanating from. That wire going to the coil from the motronic is doing nothing. No resistance. No power. Its just dead. So before I peel apart the wire harness I'm gonna see if this works out for me. Know where I can find out what resistors are in this thing? Its charred pretty bad I cant make out the color code on it. 

[dirtrider]

56 minutes ago, jermaine_rider said:

It appears that there is a fried resistor in the motronic. I'm gonna try and fix it. Rather  give that a shot first since that is where the problem seems to be emanating from. That wire going to the coil from the motronic is doing nothing. No resistance. No power. Its just dead. So before I peel apart the wire harness I'm gonna see if this works out for me. Know where I can find out what resistors are in this thing? Its charred pretty bad I cant make out the color code on it. 

Afternoon  jermaine_rider

 

That trigger wire between the coil & the Motronic gets it's power from the low side of the primary coil, all the Motronic does is trigger it between ground & open. 

 

I have no idea on the resistor size. You can usually find a used Motronic on E-Bay fairly cheap. 

[jermaine_rider]

50 bucks for a used motronic and I am back on the road. It was a long, frustrating, aggravating, informative, inexpensive, near fatal experience that I wouldn't wish on my worst enemy. But my hats off to D.R. for his invaluable insight and contribution to the outcome of my 3 month long battle with the oilhead. If you get compensated for your role here as the Oracle, they aren't paying you enough. GIVE THAT MAN A RAISE!!! Thanks again sir. Hopefully I wont be needing your services again anytime soon.