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It has good fuel pressure 55+psi
It has spark but it is weak. I know the spark is weak, because the timing light will not pulse on the spark plug wires but will pulse on the coil wire. I have used the timing light on these wires before when the truck was running well, and I checked the timing.
I can get it to start, but it misses at low rpm and of course wont idle.
I OHMed the plug wires and they are new and in spec.
I OHMed the coil and it's in spec.
I used a test light to test coil neg/tach to ground. it flashed brightly.
I checked the coil primary wire connections and cleaned them.
I checked for battery voltage at the coil and even jumper'd battery voltage to the pin. I tested the neg/tach wire between battery and pin, and its over 10kohms. I tested resistance between that pin and pin 2 of icm and its under 5ohms.
No stray voltage at pin2.
I swapped out ICM/Dist/Cap, with no change.
I swapped out coil with no change.
I feel like I should be looking for a bad harness plug, harness wire, grounds...
I have been reading through the repair manual, but I could use some guidance.
What would cause a weak spark on this TFI ignition system.
Thanks
Joe
Last edit: 1 year 4 weeks ago by joelindsburt. Reason: additional info
Lot of old Fords lately! I don't have any real experience troubleshooting those old systems, but I wouldn't take the timing light test to the bank. Not saying you're wrong, but I would only be satisfied with checking actual spark strength and intensity with a spark tester at the coil, at the distributor cap feed and distributor output before calling weak spark.
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