Hey all,
Got a '90 F250 2wd 351 auto that I'm working on for my neighbor. I'm a mechanic, but this one has me pulling my hair out. I know I'm missing something stupid, but I just can't figure it out. I have searched and searched this site and others today, tried almost everything and still can't figure it out.
I've got fuel, I've got injector pulse, I've got battery voltage to the coil, I've tried two other coils, one new/one known good, I replaced the pickup in the distributor, but really couldn't see how that would be it since I had injector pulse. I just plain do not have any spark coming out of the coil. Once in a while I might get a little, but I'd really call it none. The truck actually ran for about a minute yesterday, then died. I can't get a pop, backfire or anything out of it. The truck just died going down the road. Why can't I get any spark?
Help!

Travis

 

My guess would be the TFI ignition module. Many parts stores can test them for you.

The Hall Effect (aka PIP) sensor instructs the module to fire the coil.

 

Already tried the module with a know good one, forgot to mention that. That was the first thing I suspected.

Travis

 

Yup. People always overlook the TFI about it because it is not mounted near the rest of the ignition, it's on the drivers side fender well toward the firewall. Unless it is in a different place on your truck.

 

This one's on the distributor....

Travis

 

One of the coil wires comes right from the ignition switch: +12v. The other wire is grounded by the TFI module. Unplug the coil connector, check which pin has +12v and which pin doesn't, then check for continuity between that pin and the coil pin on the TFI connector:

 

Oky-doky...green w/yellow tracer. I have good continuity there.

Travis

 

Hook up a test light to the TACH TEST (negative) of the coil, the other end to a ground, have somebody try to start it with the key switch, the light should blink. Does it?

 

Yep, it does. And it's brighter than the positive side. I'm using a Snap-On test light, though....for everyone that don't know, it does make a difference sometimes.

Travis

 

That implies the PIP is instructing the module to fire the coil, and implies your problem lies between the coil and the plugs. I'd check the distributor cap & wires, especially the center wire connecting the two.

However, a brighter light there than at the other side might also indicate bad connections or wiring to there.

I don't know anything about Snap-On test lights being brighter or dimmer than any others....

 

I'm just trying to get spark from the coil right now....Got a good spark checker on the end of the coil wire, and yes, I've tried two other coil wires also....the only thing better than my spark checker would be my bare hand, and I'm just about there.

Travis

Edit: Some Snap-On test lites seem to light up pretty good even with low voltage, which can fool a guy sometimes. I've had mine several years and I'm used to it, but my instructor for Specialized Electronics Training demonstrated this in one class. Out of three different test lights, the cheaper ones seemed more "accurate" if you wanted to eyeball the voltage.

 

Let us know what it is when ya figure it out, would ya?

 

Absolutely.

Travis

 

This might help:

Ford Ranger/Bronco II TFI Ignition Diagnostics

 

So, you have output from the coil so there is no need for a primary and secondary resistance check on the coil.
you already did a PiP/tfi check circuit check
you have output from the coil so an ignition coil voltage supply check is not necessary.
Did you do a spout to ground check as well?
when you checked the TFI/pip did you examine the condition of the spade terminals, were they loose or carbonized? Is the rotor defective? Bad #9 wire connection?