Vehicle-1978 F150 with a later model 351c-the motor has electric choke on carb but vehicle does not have harness to power it up.. as well there is a sensor on throttle linkage that does not even make contact with the linkage.. but is plugged in to a single wire connector, no idea..

Condition- cranks strong, fuel pressure good, but no spark at plugs. Truck has ran just fine since bought 4 months ago. Went into the store last night, came out and my nightmare began.

Current diagnosis and repairs-no bad wear on cap points or rotor tip found (cleaned points and tip anyhow) Wires and plugs are six months old. Next, found no spark out of coil, tested coil and found 4ohms between primary contacts, as well in between each primary and secondary in which should be higher if I'm not mistaken. So part replaced and still nothing. Tested pickup in distributor and found open circuit between orange and purple wires and good continuity on black wire to ground screw distributor. Replaced pickup and still no spark. Next, read a forum and found the ICMs are known problems. No testing of part I just replaced it. Still no spark. Went to Voltage supply to coil (red/grn wire) and find 7.2v when key moved to pos2 and 8.1v when key at crank. Believing I should have 9-12v at +contact on coil. Traced low voltage all the way back to the key switch output. Found 12.5v supply to key switch. Replaced Key Switch and I now get 9.5v at + contact of coil. Next, Rookie mistake and did not inspect rotor movement, rotor does not move while engine cranking. Pulled distributor and found roll pin holding drive gear has sheared.(1st for me) Replaced roll pin and STILL no spark. Except one single bright blue spark out of coil if wire is grounded while cycling key from crank to off. please someone help. What am I missing here?

Parts replaced at this time-
Ignition switch
Ignition module
Ignition Coil
Distributor pickup
Drive gear roll pin
cleaned ground cable contact at battery and block

 

confirm the roll pin didn't shear again...something caused it to shear once and if you didn't identify that, it could have easily happened again... if the distributor is still rotating, use a test light to see if the negative side of the coil flashes while the engine is being cranked. If no flash, there is a problem with the pickup coil or the ignition module or related wiring.

 

Thank you for the reply, I did recheck the rotor movement and it was still operating correctly. When I had the distributor I did verify the oil pump turns freely. I did notice that the bearing on the distributor is feeling worn though. I kept inspecting and trouble of trouble appeared.. Battery failed load test, ground cables correded internally causing high resistance, and the frickin starter was loose causing a 2v drop. Replaced all parts an secured starter and still nothing.. Then retested everything from the beginning and the stupid pickup in distributor (brand new) had 8ohms across purple and orange.. Warrantied the part and boom she's alive. When tax time happens I'm going to upgrade to that hei system. But for now shes back in action. Again thank you for your reply.

 

I would think twice about that HEI. Yes, you had a part fail. That happens. You can use the HEI module triggered by your Duraspark distributor, but the cheap chinese HEI distributor shafts have been known to snap, not just a roll pin. When that happens, it usually grenades the whole engine. Just something to consider.

 

X2.

The Dura Spark ignition is a good system. Be sure to use Motorcraft parts and the systems are nearly trouble free.