123/tune+ Redux

[Chris_B]

On 5/28/2019 at 12:32 AM, Simeon said:

Have you got a diode in circuit with your tacho adapter wiring?

 

Wondering why you asked this? I now have my 123 ignition and MSD6AL running just fine, but still am having bizarre problems with my instrument panel (mostly the temp gauge needle jumping around- e.g., when I operate the turn signals, the needle jumps up), but yesterday I drove the car for an extended period time (it was completely warmed up) and when I turned the ignition key off, the motor continued to run 5-10 secs (tried it a couple of times). This suggests that power is feeding into the ignition circuit from somewhere, even with the key off.

[man_mark_7]

4 minutes ago, Chris_B said:

 

Wondering why you asked this? I now have my 123 ignition and MSD6AL running just fine, but still am having bizarre problems with my instrument panel (mostly the temp gauge needle jumping around- e.g., when I operate the turn signals, the needle jumps up), but yesterday I drove the car for an extended period time (it was completely warmed up) and when I turned the ignition key off, the motor continued to run 5-10 secs (tried it a couple of times). This suggests that power is feeding into the ignition circuit from somewhere, even with the key off.

 

I had a weird experience once, as a young hot rodder, when I added an electric fan to my '76 Camaro. As long as the fan was still spinning down, the motor kept running. I obviously had wired it into the ignition circuit and the fan was acting as a generator.

 

M

[Simeon]

On 6/11/2019 at 3:47 AM, man_mark_7 said:

 

I had a weird experience once, as a young hot rodder, when I added an electric fan to my '76 Camaro. As long as the fan was still spinning down, the motor kept running. I obviously had wired it into the ignition circuit and the fan was acting as a generator.

 

M

 

This is the usual reason for the diode as it is easy to ‘power on’ the MSD through a back feed.

 

I used the diode included with my ignition between the tacho adapter and the Ignition box (mine is a Summit Racing knock off) and the 123. While both the ignition and the 123 are probably designed to cope with the flyback voltages likely to be seen from the tacho adapter, I thought that they might both be more reliable if they were spared the pulses by blocking them with the diode. 

 

Don’t think this is related to your issue unless the tacho adapter is interfering with your instruments. This is not necessarily impossible but would be only likely where there were other wiring deficiencies (most likely a ground problem which you know you don’t have). If everything is working properly then you wouldn’t get any more interference from that than you would your own Kettering ignition. 

[Chris_B]

MSD tech support suggested that I am getting power fed back through the B+ circuit from the alternator, and said I should install a diode in circuit to prevent that. Great idea, except that seems like it would prevent my no or low alternator warning light from working...

[Chris_B]

Following up on this. It turns out that my problem (motor running rough/dying when significant load put on system [e.g., headlights and/or blower motor on] with my 123 dizzy) was not resolved at all. Due to what I consider in retrospect to be shoddy troubleshooting on my part, I blamed the 123 unit, because when I reinstalled my Bosch dizzy (with Pertronix), the problem went away. Clearly, the 123 dizzy requires more power than a Bosch dizzy with Pertronix. Makes sense- more electronics.  

 

JIC, I decided to check out my charging system, including resistance and voltage drop on every cable. I increased the size of the cable to my bus bar that I have my accessories connected to. The system voltage at idle (blipping it up so that the had alternator kicked in) was >+14V. I thought all was good on that side.

 

I have been driving the car during the day to tune my carbs- everything seemed to be OK, until one day the motor started to cut out when I used the turn signals. WTF? It was around that time that I noticed that the voltmeter on the 123 dashboard was showing the voltage dropping below +12V when I turned on the headlights and blower. I thought this can't be, but decided to check system voltage. To my amazement, the 123 was accurately reporting system voltage, which was dropping below +12V with the headlights on and blower motor set to 1 (more would cause the motor to die so I couldn't measure). 

 

I have read about this happening- an alternator apparently maintaining voltage, but craps out with demand. I don't have the capability to measure amps in the system, but I have concluded that the alternator is bad (likely, defective diodes). This is an 80 amp 318i alternator, so it should easily have been able to keep up with the demand from the lights/blower. I have ordered a replacement and will report back after installing it.

 

 

 

[Chris_B]

I am embarrassed to admit it, but It turns out that my problem is likely being caused by poor chassis ground. I R&R-ed the alternator, with no change. I then replaced the 123 dizzy with my original Bosch tii dizzy with Pertronix, and this caused many of the symptoms to go away, but when I measured the system voltage (using the same location for the ground as I had used to ground the 123 dizzy- this was my big mistake), it still appeared that the voltage was dropping below +12V when I applied a load to the system (e.g., headlights on, heater fan up to 3, etc.). The Pertronix ignition clearly is less sensitive to voltage drops than the 123 dizzy, but that only makes sense.

 

I had measured the resistance between the battery and that grounding point (the bolt holding the coil bracket) and only saw a few 10ths of an ohm. That clearly was not OK for the 123 dizzy, which has a separate ground connection. Checking the voltage using a ground on the motor shows that there is no significant drop when a load is applied.  I will need to install a stout chassis ground to resolve this.

 

Also, while I was swapping the dizzies in and out, the Bosch with Pertronix suddenly stopped working. The motor had been running fine with the Pertronix and I shut it off after setting the timing to lock it down. When I attempted to start the motor again- nothing. It would crank freely, with no hint of ignition. WTF? I swapped the 123 dizzy back in and it fired up on the first crank. Go figure. Now that I know the problems I have been having are not due to the 123 dizzy, I can stay with that.

[Dudeland]

If you leave the key on, it burns out the pertonixjn short order.


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[Chris_B]

So I understood. I don't believe I did that, but who knows. I had to have the key on quite a bit for a lot of the testing I was doing. The strange thing is the motor was running while I was setting the timing, and I shut it off so I could tighten up the dizzy retaining bolt (key off during this process), went start the motor and nothing.

[Dudeland]

6 hours ago, Chris_B said:

So I understood. I don't believe I did that, but who knows. I had to have the key on quite a bit for a lot of the testing I was doing. The strange thing is the motor was running while I was setting the timing, and I shut it off so I could tighten up the dizzy retaining bolt (key off during this process), went start the motor and nothing.

 

Sorry,  I was commiserating with you.  I have done the same thing the first time I put one in Bug.  I was one of the first folks to swap one out.  They were like $300-$400  back then, and I burnt my first ones out.  Got my key on, changing settings on my radio, and no joy.. 

 

Glad to see that you got it fixed.