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View Full Version : 79 f150 no spark??


04SVT-L
03-14-2010, 02:38 PM
ok guys im new here. i got a 79 f150 with a 351m and a 4spd and im kinda stumped on this one. heres the thing, if i wake up in the morning and start the truck, it will fire right up no prob. and i can drive the truck all day, as long as i dont shut it off. when i shut it off it will crank and crank but not start, unless i leave it sit for a long time. and when im cranking it when i go to start it again, i have very weak spark and its not while im cranking. the truck will sputter after the key goes back to the on position. i replaced the ignition module(4times) coil, wires, plugs, cap, rotor, starter solenoid, ignition switch module under the dash and checked all the wires.. im stumped and can not figure this one out. any help would be greatly appreciated

cipsmithers
03-14-2010, 02:41 PM
hmmm. cant help you, but welcome to the site! someone will come up with an idea

04SVT-L
03-14-2010, 02:44 PM
yea thanks.

m78
03-14-2010, 02:51 PM
check all your grounds

chuck101st
03-14-2010, 02:54 PM
The coil pick-up in the distributor will cause that too...

04SVT-L
03-14-2010, 04:23 PM
The coil pick-up in the distributor will cause that too...

yea just got back from the store and bought that. im gona go try and put that in in a few min. ill let ya guys kno soon

blacksnapon
03-14-2010, 04:28 PM
yea just got back from the store and bought that. im gona go try and put that in in a few min. ill let ya guys kno soonCareful, its easy to break the gear on the bottom of the distributor when going back together.

Mil1ion
03-14-2010, 09:15 PM
pure coincidence :)

check the connectors and wires to the distributor.n these are know to cause intermittent ignition problems.

also make sure the ignition module has space under it to allow cool air to flow under it.....so the IM doesn't overheat

Truckin4life
03-14-2010, 11:34 PM
Weak spark... Does it have good spark in the morning?
Sounds like vapor lock to me, my truck used to do it all the time. I dont remember what i did to fix it either...

TexasRho83
03-15-2010, 10:27 AM
Timing issue?

1985 Ford F-150
03-15-2010, 12:14 PM
I bet its the ignition module gettin hot.

04SVT-L
03-15-2010, 06:35 PM
it was just the magnetic coil pick up in the distributor. its fixed and running good now
thanks guys

redneckryder
03-15-2010, 08:14 PM
the starting issue sounds like a float problem. My F-150 did that cause it was floodin itself out. when you shut it off and try to restart it, hold it to the floor and see if she starts. if so, rebuild the carb. If you KNOW it's an electrical issue, disregard the above statements......

redneckryder
03-15-2010, 08:15 PM
oops...didn't see there was a page two....my bad. glad you got it fixed....

Mil1ion
03-15-2010, 09:55 PM
change your thread view to 40 posts

63fordf100
09-24-2010, 09:11 PM
my cousins minivan had that actully, we took the distributor cap off and ran a bead of silicon in it and it sealed it up!

rjphillips
09-24-2010, 10:50 PM
Sounds like distributor, but check the opposite plug on the module they can corrode and not make good contact to the new module.:hammer:

BKW
09-25-2010, 02:52 AM
The early DuraSpark ignition modules were notorious for failing. Ford techs used to refer to them as NeverSpark.

The three step scenario of a failing DuraSpark ignition module:

1) Module overheats, engine dies. Module cools down, engine re-starts almost at once.

2) Module overheats, engine dies. Module cools down, engine re-starts in a hour or so.

3) Sooner or later, usually sooner, the module overheats, BURNS OUT. Now the engine will not re-start.

Since the module only fails when it overheats, taking the little darlin' to an autoparts store to be tested, usually doesn't work...unless it has burnt out all together.

mofunone
07-22-2013, 06:39 AM
ok guys im new here. i got a 79 f150 with a 351m and a 4spd and im kinda stumped on this one. heres the thing, if i wake up in the morning and start the truck, it will fire right up no prob. and i can drive the truck all day, as long as i dont shut it off. when i shut it off it will crank and crank but not start, unless i leave it sit for a long time. and when im cranking it when i go to start it again, i have very weak spark and its not while im cranking. the truck will sputter after the key goes back to the on position. i replaced the ignition module(4times) coil, wires, plugs, cap, rotor, starter solenoid, ignition switch module under the dash and checked all the wires.. im stumped and can not figure this one out. any help would be greatly appreciated

I just discovered this site. Your problem is the electronic pickup coil. it is in the distributor it is usually blue with an upright rectangular magnetic metal piece on its face. its the thing on the end of wires which protrude out of the side of the distributor... I just changed one yesterday.They are easy to change but tedious.. be careful. Take the top off dist, take off bug take off second plastic section of dist.then undo one screw holding a ground and holding the wire harness to the inside of the dist,, then remove tine c-clip of of vacuum advance... then take a couple heel bars and pry the star up off of the dist shaft( pry at the shaft, not at the end of the star, you might break it) ,,,it has a tiny roll pin, dont lose but you can pry the star gear up off of the shaft, the roll pin will usually stay,,,,, dont lose the roll pin.. then after this is complete you must remoce a C shaped wire from around the dist shaft,,, it is big enough to go around your finger but very thin,, dont lose it,,,,,,, then after that just pull straight up on the pickup coil and it will slide off in your hand,,, go buy one for 18 bucks from napa and put it all back on,,,,, i repeat,, there is a small square hole in the dist,this could lose any or all of your small parts so hang onto the small c the bigger c and the roll pin and it will all be ok. put it back together,, Hope this helped. This to me seems to be the problem way more often than any other component of the ignition, in my humble opinion one should change this first (if he is a parts changer instead of a mechanic.. good luck.

JaxLen3
07-24-2013, 05:54 PM
I see that the problem is fixed, but sometimes these things go bad because of poor grounds at various locations as well as poor connections. :suspicious:

Food for thought: Make sure every ground is right and tight...sand the metal where the Solenoid touches the fender or fire wall, as well as under neath the Ignition Mod box. Replace the old bolts with bolt thru to nut connections. They need to have tight connections, and when you R&R these parts over the years, they can get loose and corrode causing bad ground. Also, make sure you use copious amounts of dielectric grease on all those places you sanded as well as ALL of the wire connections too.
Grace to you.

tpolk
09-15-2013, 09:14 PM
yeah not sure what to tell you on that one sounds like it might be a resistsnce issue in the ignition circuit maybe a corroded ground or something try getting a multimeter and look up the specs for doing a resistance test on it cant really help you much past that one

Mil1ion
09-18-2013, 10:51 PM
If your Ignition module does not have 4 little shoes on the bottom of it to allow air to pass under then you will have ignition issues.

Buy the proper motorcraft I/M

The gap should be about 1/4"

Big Jim F150
09-19-2013, 12:24 AM
I had the same problem with my 1978 f-150 Ranger Lariat,
with a 351M and automatic, I had the distributor rebuilt, but
that was a short term cure, then I had found out that I had a bad
pickup wheel in the distributor, I had taken to the local Ford dealer
to get this taken care of, they had also rebuilt the distributor, and had
reused the original pickup wheel with the idea that it still was good, but it
had turned out that my old one was shot, but the best part is that
They didn't charge me for labor, and all that I had to pay
for was the pickup wheel, now the truck runs like a dream.

bucks77ford
09-19-2013, 11:29 AM
Pretty big gap between posts on this thread :)

Big Jim F150
09-22-2013, 09:15 PM
Got my pickup wheel replaced in my '78 f150 Ranger Lariat
And it runs and starts like a dream, and now it goes like a raped ape
I hat replaced last week , and I have driven the truck a few times since.