Solved an interesting problem with what I thought was my TFI module last night (I was wrong in thinking it was the TFI module).
A while back I relocated my TFI into the core support. It's mounted it on a heatsink with a PC fan to try to mitigate heat issues. Definitely cleared up a few by doing this, but something continued to feel "off" at times. Module was staying stone cold, yet I was still having timing issues during warm up cycle and under load. Hm.
Since day one, getting the timing on this truck set was a b*tch. Setting to 10 degreed BTDC was a daunting task, as the timing marks would usually "walk" around +/- 2 to 3 degrees with a light on it and the SPOUT connecter removed. I had chalked this up to "old tech" and bad TFI modules. Holy crap was I wrong.
On a whim, I tore apart my distributor, tossed it in the ultrasonic cleaner, hit the shaft with polishing compound, and replaced the hall effect sensor with a new Motorcraft brand name one.
Fired it back up after losing the tie down bolt down the back side of the engine at least half a dozen times (seriously, who designs this crap...), and put the timing light to the crank pulley.
Zero. Walking. Swiss watch precision. I was giddy. I've never seen an engine this precise in holding time at idle. I can literally set timing to fractional degrees now.
I set to 10 degrees BTDC and went for a drive.
The idle and under load performance is night and day. If the tie down bolt wasn't my mortal enemy, I'd absolutely shoot a video of the before and after. I cannot recommend this highly enough if you're reading this and have a 2.9 that just won't time properly, or stutters, or hesitates, CHANGE YOUR HALL EFFECT PICKUP. They're cheap. Odds are it's a 30 year old sensor, and has been through countless heat and cool cycles. This sensor allows your tfi to keep time in your engine, and your EEC to advance and retard it. Do it right, buy a Motorcraft, and change it. Clean and pre-lube your distributor while you're in there. Your 2.9 will thank you.
I can't help but wonder how many 2.9s hit the crusher over that sensor.