2.9L TFI Weird Issue

[Uncle Gump]

It's been awhile.... but I'll try.

The tach wire between the negative side of the coil and TFI allows current to flow from the 12volt positive side of the coil... through the primary windings in the coil to ground at the TFI. It's hard to see "pulsing" 12v to 0v on that wire... unless you have an oscilloscope. The update rate on a DMM isn't fast enough to show that 12 to zero change... it will typically display a varied voltage which would be half of battery voltage... depending on crank speed.

 

[BoomTexan]

It's been awhile.... but I'll try.

The tach wire between the negative side of the coil and TFI allows current to flow from the 12volt positive side of the coil... through the primary windings in the coil to ground at the TFI. It's hard to see "pulsing" 12v to 0v on that wire... unless you have an oscilloscope. The update rate on a DMM isn't fast enough to show that 12 to zero change... it will typically display a varied voltage which would be half of battery voltage... depending on crank speed.

I figured that it would do that, the VAC to VDC conversion typically hits like 12/1.414, but in that case, I should be seeing like ~8V, not 4 like it is currently. For this sawtooth, I'd expect 6, but I'm not hitting that either.

Just to see if my logic makes sense, does this statement make sense to you: the coil just isn't activating at all for some reason anymore, and given that I've cycled two known good TFIs through it, the only failure point should be my new distributor, right? (especially given wiring diagram linked below)

Of course as soon as I get the motivation to get outside and work on this, it starts raining.

 

[Uncle Gump]

You have to remember or consider what battery voltage is while cranking. That signal line should be roughly half of battery voltage.

 

[Uncle Gump]

The fact that you can see a voltage in that tach wire other then battery voltage tells me that the hall effect is triggering the TFI.

I also read that you said ballast resistor. Where is this ballast wired in?