I have a 79 F150 with a 429 its got a duraspark ignition unclear if its i or ii.. However.. sort of a long background what can I say I'm a girl and i hate to omit details! Pickup has had a finicky ignition last few years, turn to start click only maybe nothing, retry and it may fire right up. Last winter it started to cut out under load or acceleration it would just cut out really quick then go along fine. Seemed like it was only when cold then it go worse and started to do it more often.Then one day wold not start.. I had no spark inspected ICM plug was melted replaced ICM and still no spark, replaced coil fired ran for 3 seconds and died..inspected mag. pickup and wires were totally burnt? however both unattached to magnet piece replaced pickup (stator). Still would not start still backfiring on crank timing was off by 30 +/- degrees removed all plug wires and rotated one post to get timing in an area I could adjust back to 12 BTDC ..Yea!! it ran!! not great but it ran.. It was terribly hard to start still slow cranking not firing but once you got it running it would run under load it was awful though cut out backfire out the exhaust... Now its been run a couple times as a test drive and thats it and now Im back to no spark... I found a short to ground in the Courtesy lamp circuit and pulled that fuse as Im more anxious to get it running than get courtesy lights fixed.. but short may have caused more problems??? Ive tried to start again and now no spark at all so I replaced coil fearing it'd been killed by short... still no spark tested NEW stator and it was open!! So i replaced it again with one i pulled from another pickup OK!! now I'm getting spark but its weak still won't start.. Ive pulled ignition switch and gone through test on it and I'm at a loss I've owned this pickup 17 years and rebuilt the motor in it 12 years 60k miles ago its my baby and its been out of service for ten months!!! please help i don't know where to look next i feel like I'm chasing a ghost... alternator regulator? starter solenoid? what else am I missing??
Sorry so long but i feel like I've covered a lot of bases so far thought it was relevant..... Thanks in Advance!!!

 

If timing was off 30 degrees she has jumped time. Most likely keeps skipping a tooth or 2 sometimes when its turned off. You stated when it first started it was slow to crank over. I would suspect the short to be somewhere in starting circuit.

 

I would suspect that you have a bad short/chaffed/bare hot wire some where. Instead of replacing that ICM so fast, I would of been more interested in finding out WHY that ICM plug was melted.

Also reading about all the rest of the damaged stuff, I again suspect you have a hot wire grounding out and burning up items.

Look under the hood for damaged wires like, smashed, burnt on exhaust, kinked in between body panel, rat and or mice chew marks. Ck down along the dvrs side frame rail, looking at the harness running down the inside of it and very close at times to the exhaust sys? Behind the dash cluster for signs of melted wires.

Insp ANY and all add on elec items, radio, amp, lights, ck the alternator wiring for signs of damage or being spliced incorrectly for power. I doubt that a bad courtesy light wire could cause all that damage, but maybe it did other harness damage. I figure the fuse would of blown....

X2 on timing off so much, sounds like it might of jumped time....I know you have had it for 17 years, but maybe the PO did some wiring modifications somewhere and it has finally let go?

 

When the timing was off did you check to see if the roll pin in the distributor gear sheared?

 

Check wiring...

But Hard or Slow crank sounds like it jumped a toof on the timing gears and chain...

Might have to dig into the front a bit and have a look see

The ICM should have two plugs on it, I'm going to guess it was the one going to the truck harness, and not the one to the engine. Check for voltage at the plugs? I donno... throwing things out there. But does worry me that it was melted.

Oh, and check the voltage at the coil with ignition on with a multimeter! should be around 8v

 

Thank you guys for taking the time to give me advice!! GatorFord88 "Most likely keeps skipping a tooth or 2 sometimes when its turned off" could you tell me how this might happen?? Im not sold on the timing chain skipping a tooth theory yet as it ran totally fine aside from the cutting out prior to this mess. As the hard starting goes IS it possible to bend a valve or pushrod from backfire?? When cranking the carb spits some fuel back cup and out but again is this a valve issue or electrical and Im getting a weak spark at the wrong time and just blowing back out the carb? I still think I have an electrical issue is there another test I'm forgetting to find short.. Ive disconnected neg cable at bat voltmeter to cable and ground post it showed 6.3v until I pulled courtesy lamp fuse, pulled fuse and it showed something low like .3v still not ideal but this is an old ranch pickup.. not abused but the babies and the cows have come first the last few years I will check the harness along driver side frame rail I've gone over most every wire under the hood and looked the best i could under dash.. the stereo no longer works I think I'll pull it to give better access and be sure its not the wiring culprit. what about the external Voltage Regulator for the alternator?? can I test it is there anyway this could be suspect??

 

If that roll pin is sheared in the gear that drives the distributor it will turn on the shaft some

 

ALSO! I read on some other thread about putting test light to tach term on coil it should flash while cranking... And another test said I should get flash when key goes from run to off.. can someone tell me if this is correct?? I do get light when key goes from off to run.. but its touchy not a big bright light and not real consistent made me think it was ignition switch but as I said I've pulled it and done continuity test and it passes.. (unless I can get more specific numbers for what the resistance should be between terminals) ok back to tach terminal.. while cranking light sort of flickers but its not big and bright is this norm..??

 

Montecz Ive pulled the dist. twice roll pin is intact, gear is good, even went in and looked at the advance weights all is well....

 

Okay, the tach side of the coil should pulse every time the distributor sends a spark

 

It will put a smile on your face, it did on mine.

 

Are we talking a big bright 12v light pulse or a ho hum kind of flicker

 

Bill Ive been told that before!! at this point i don't know what direction to look or go Ive put so many dollars at this point into ignition I don't want to start over.... Ive payed 2 different mechanics to look at it with me gotten no where really... I'm convinced its electrical husband thinks its timing chain... he's a cowboy though... so really?????

 

It should be about the same voltage as what goes into the coil since it is your coil's ground

 

And I know I'm all over the map with questions.. sorry! Since I pulled courtesy lamp fuse and lost the 6.3v short that showed across neg post and cable. Is that (pulling the fuse) sufficient to eliminate the circuit or the short??