1985 ford F150 with TFI ignition, replaced the module, coil and dist, still no spark, truck ran great , then suddenly after maint on carb and dist, quit running. power present at coil and dist harness, I am stumped, anybody help ??????

 

What maintainence did you do on distributor.The rotor isn't laying on the bench is it?

 

no its not, it is in the proper position inside the dist. the parts have all been marked prior to disassembly and reassembled in the proper order. It has simply lost fire.

 

Get a cheap ($4.00) test light. Connect the ground alligator clip to battery ground.
Probe the negative side of the coil primary. The test light should be on when the key is in "run". If the light is dark, check the positive side. If that side is lit, the coil is bad or the TFI module is shorted, or possibly the harness is shorted. If the positive side of the coil primary is not lit, the feed from the ignition switch is bad.

Now crank the engine (use a remote start switch or a helper). The test light should flash as the engine cranks. If the light does not flash, the TFI or pickup or grounds or wiring to same are bad. If the test light does flash, but you do not have spark, the problem is in the coil, the high voltage feed to the distributor cap, the cap, or the rotor.

If you run these tests, you can narrow the problem to the high voltage or low voltage sides of the system, and maybe narrow it down beyond that, depending on what you find.

 

I had the exact same thing happen to me on my 84 F150 300 six. I installed a new carburetor, got everything hooked up then it wouldn't start. I almost lost my mind trying figure it out! Like the other guy said, get yourself a test light ( I prefer a multimeter) and check all your fused links under the hood. Make sure you have power on both sides of the coil...pos and neg. Also check the plug in harness for the TFI module, you should have power there. You should have power at your coil plug and TFI module plug if you turn the key on. If you don't have power at the plug, get yourself a straight pin and poke it through the insulation on the wires then touch it with your test light. You may find there is a break in one of the wires and you won't have power where you need it. If you have power to your coil and your module, and still no spark; then either the coil, the module is bad or your distributor is bad. Unfortunately I have not been able to find overhaul parts for Ford TFI distributors, you would have to buy a reman distributor they run $60 at Advance Auto. In my case it was a broken wire on the coil harness, the wire appeared to be okay but after probing around the the trusty ol straight pin I found a break in the wire. Also one of the terminals on the plug was broken. I went to the junkyard and cut one off another truck and soldered and spliced it back into my harness. She runs like a champ now! Good luck!

 

The multimeter is better for measuring that the correct voltage is getting to the coil primary plus side, for checking resistances, and for checking for ground drops.

However, the multimeter is nearly worthless for determining whether the TFI is firing the coil or not -- the flashing (or not flashing) test light works way better than trying to decide if "7.5 volts" on the multi-meter means the multimeter has decided the AC waveform is about the equivalent of 7.5 dc volts (and the TFI is firing) or whether "7.5 volts" is a DC level that reflects some amount of voltage drop due to the starter loading, (and the TFI is dead as a doorknob). I know I can't tell the two conditions apart with a multimeter, and I've tried.

 

Not sure if you have already gotten this issue resolved, but I have troubleshot a similar issue on my 84 F250/460cid V8... As for the multimeter for measuring whether the coil is firing, if you have a good meter with frequency measurement, you can probe across the two coil terminals (+ and -) and see the frequency. It will likely be around 500 Hz when cranking. If you see this frequency, then your module is working fine during cranking. If no signal, then the module is dead.