No coil spark? Tried tons o stuff, what next?

[monkei]

A lil' background: My buddy has a 90 5.0 bronco. It had been sitting for ~6mo and had its rear brakes done and was then drive to take care of smog. After smog, it died on the way back home and wouldn't start.

We've been trying to troubleshoot the no start problem for days now to no avail. We get no spark out of the coil wire (to the dist). We've tried a rebuilt dist w/ new stator & TFI, a new coil, a new ignition switch, and a rebuilt EEC in desparation. None have worked. The new ignition switch we're using isn't bolted to the column but is loose and being actuated manually w/ a screwdriver.

The coil has passed resistance tests, and is getting 12v at coil negative(-), oscillating between 12 and ~6v at coil negative when cranking. Should it be dropping even lower than 6 to trigger the coil? The Chilton manual just says to check coil negative while cranking with a test light. We tried that and got a small arc and heard the fuel pump cycle as if the eec had been turned off & on (EEC protection of some kind?), so we decided not to continue trying the test light.

We looked at Chilton tests we could do and checked pins 1,2, & 3 of the TFI harness and found the voltage to be low at pin 1 (~4-5v) in RUN, and pin 3 (~4-5v) while cranking (the voltages on 1-3 are all supposed to be 90% of full battery voltage). Pin 2 voltage is fine. It has been the same with both the original and the rebuilt EEC. The wire for pin 1 (grey and orange) from the new EEC was checked at a fenderwell connector and has the same low ~4-5v reading.

What would cause pin 1 (PIP out) and pin 3 (START signal) to be low voltage.

At this point we don't know what to do. Are there relays, fusible links, particular wires we should be checking? Any help is greatly appreciated.

[PaulW]

wires in the coil connector?
2 different Bronocs , both has bad connections.
PW

[blueoval8493]

I've had 3 different trucks loose spark because of the wires that i think paul is talking about that go into the coil. They're not really sealed from the elements at all. I always put a new end on then fill the hole with silicone to try to keep moisture and crap out. I've found a few trucks that the tab that holds the plug in the bottom of the coil was broken off so that whole plug was loose and cause poor spark.

[PaulW]

I've had 3 different trucks loose spark because of the wires that i think paul is talking about that go into the coil. They're not really sealed from the elements at all. I always put a new end on then fill the hole with silicone to try to keep moisture and crap out. I've found a few trucks that the tab that holds the plug in the bottom of the coil was broken off so that whole plug was loose and cause poor spark.

======
Roger - connector at the coli. I have the same fix now.
Check out the pins and connector seating.
I even bought a non ford coli with no tab. Bought in SF Baja. No options.

BTW, same problem on the MAF connector on the 72 with a 92 5.0. That one took some time to isolate out in the back woods.
NAPA sells the replacement connectors for coil and MAF.
Both oem connectors are crappy design. Replacements are identical, but at least new.
Sigh
PW

[TurboJoe]

I had a main power relay partially fail on a ranger I had ( low voltage out ) and it wouldn't light up the computer, No fuel pump prime and no spark...

Joe

[monkei]

we have fuel pump so the power relay ain't it. we also have voltage at the coil terminals. the coil negative does not seem to be dropping low enough in voltage to cause spark (the test light just dims rather than flashes)

checking PIP & SPOUT in AC (200v ACV range was the lowest the voltmeter would do), we get ~25v before cranking and it drops to ~21-22 ACV when cranking. Totally confused by that.

Tested the second to lowest pin on the TFI harness (COIL) for a stray voltage and found ~2v. Tested this wire on the EEC side of the ignition suppression resistor and got ~4v coming out of the EEC. This is even after we swapped out the original ign. supression resistor and associated wiring, so we think we've ruled out a short on this wire between TFI harness and the connector on the drivers side plastic fenderwell.

Also unhooked soil negative and tested resistance to battery negative. It was supposed to exceed 10k ohms, but read almost zero.

We are pretty much at a loss here. The AC test seems inconclusive or maybe it needs to be done on a meter that goes lower on the AC scale? Don't know what to do with the stray voltage...

[TurboJoe]

Any way to swap for a known good computer? If your grounds are good it might be worth a shot. I'm not one for throwing parts at cars but you seem to have a good grasp on how to chase a wiring diagram and you have followed the insructions well, I don't see why you would miss anything myself. Maybe mail your computer to a GoFast member and have them try it out? Shipping would be cheapish and you can't drive it now anyway...

Joe

[monkei]

unfortunately, the eec swap to a rebuilt unit didn't work. Might try replacing the TFI unit on the rebuilt distributor.

[TurboJoe]

I guess that's worth a try... I'm real curious to know what the fix is???

Joe