So, to recap. Ernie was running, but there was a bunch of noise coming through the TPS which was causing injector spikes, which was making the part throttle response miserable…and that’s being kind. So for the past few weeks I’ve been tracking down and eliminating noise as best I can.
First step: Eliminate coil triggering.
I was using the negative terminal of the coil, while it’s cheap and easy it was introducing a lot of noise into the system. As you’ll recall I build a filter using a resitor and a diode, and while it helped, it didn’t solve the problem. Going a step further I then added a capacitor, trying to create, in essence, a low-pass filter.
So screw it, time to just convert it to electronic ignition. I’ll just trigger it off the points, should be simple, right?
The actual wiring is pretty straightforward, in fact the megamanual gives a really nice drawing of how to trigger off the points and then use an external amplifier/module to drive the coil.
The input signal was beautiful; no noise, no bouncing around, rock steady in fact.
The module however refused to cooperate. I looked at it six ways from Sunday and compared the diagram to my wiring, but something just didn’t seem right…see if you can spot the problem.
If you said something along the lines of why is pin 4 & 5 getting both 12v constant and trying to get to ground (through the mS), give yourself $100, you are an electronical genius!
The revised circuit looks like this.
So, gtg, right?
Of course I’d have a bad module, and at $120 per, not exactly cheap. Luckily Rockauto just so happens to have a wholesaler closeout for $35 per. Sometimes it’s better to be lucky than good…I’ll never know either, but I keep trying.
So now it’s working, but I’ve got 100 degrees if timing because of the timing in the distributor and the timing being handled by the mS. Luckily some clever soul must have considered this because if you poke around in the ignition settings you can make them static, which will let you still keep the distributor distributing. Ain’t science grand?
I was still getting some noise so after a little searching I found some people have eliminated that by grounding their alternator case to the engine with a good separate ground, so I did that, and some put in a stereo power supply filter (basically a low-turns coil with a capacitor)
I still have some noise, but the truck is driveable now, so now I can actually use it again and get to tuning. I could eliminate a little more if I took the time to rewire and sort the wires near a distributor a little better (you can’t really tell in this picture, but take my word for it)
Overall, I’m pretty happy with it. Power is about the same, it does seem to start easier, and it’s nice to be able to tune the accelerator enrichment since I could never get it right on the Motorcraft after trying every possible combination given.
Here’s a little gratuitous video of my driving it home today.