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Old 04-11-2010, 02:21 PM   #1
southerntrax
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truck wont start....again.

well i got my old 78 f150 running last weekend. fuel pump went out. so this weekend i went to fire it up and once again just spinning over. got out looked down in the carb and i do have fuel this time. so i am guessing i have lost spark. one thing i noticed when i turn the key on my tach will jump from 0 RPM too 100 RPM. but while in the start position it never moves off of 100 RPM. i had a similar problem with my 87 250 with a no start and tach not moving. turns out it was the pickup in the dizzy. could i be having the same problem with my 78? and dose anyone know the specs for testing the pickup?
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Old 04-11-2010, 02:29 PM   #2
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The best thing to do is see if you have spark before you jump to conclusions.
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Old 04-11-2010, 03:31 PM   #3
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I've only seen the pickup either work or not. Continuity or infinite ohms. Continuity = good, Infinity = not so good. The magnet wire likes to break off right where it enters the cast resin.
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Old 04-11-2010, 04:30 PM   #4
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i have a inconsistent spark. plus its looks weak. grounded a spark plug and it would spark then not but like i said it looks weak. i tested my power to the coil with key on and i got 12v. only getting 1.6 out of the coil with the key on. haynes book said should have had 12v coming out of the coil.
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Old 04-11-2010, 07:46 PM   #5
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Check the ground screw inside the dist.
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Old 04-11-2010, 07:50 PM   #6
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you have another coil laying around? could be a bad coil
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Old 04-12-2010, 07:21 PM   #7
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messing around with the truck today i found that if i unplug the coil probe the positive wire i get 11.9 volts. but if i plug it in and probe it i get like 6 volts. and if i test the end were the coil wire goes its only 6 volts. dose that sound like a coil that has died?
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Old 04-12-2010, 08:28 PM   #8
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no
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Old 04-17-2010, 07:00 PM   #9
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anybody got any suggestions? so far i have replaced the pickup coil in the dizzy and ignition module and put a used coil on. im gonna check timing tomarrow but i don't think it could have jumped but you never know. i am still only getting 6 volts to the coil plugged in and 12 volts unplugged. jumps to like 9 while cranking. just trying to see if anyone else has ran into something like this.
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Old 04-17-2010, 07:14 PM   #10
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are you getting spark?
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Old 04-17-2010, 07:33 PM   #11
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very weak. only have 6 volts coming out of the coil. i hooked my timing light to the coil wire and it was dim. then hooked it to number one cylinder and it would flash but not consistant. reading a post on fordtrucks.com a guy was having the exact same problem and he ended up replacing the iginition module and it fixed it. i am believe i got a junk module from autozone. any one have any good luck with a certain brand or store. i know i have heard alot of people getting bad ones right out of the box.
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Old 04-17-2010, 07:35 PM   #12
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they can test the ignition module they sold you.

I would check everyting for bad connections, grounds, positive battery cables, everything.
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Old 04-17-2010, 08:00 PM   #13
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tried to get my old one checked and they said that they no longer have the tools to check modules. i've been through every ground and cleaned them. and if i was reading correctly with the key on truck not running i should have battery voltage at the neg terminal of the coil right? just making sure im doing my tests right.
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Old 04-18-2010, 10:15 AM   #14
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Could be bad contacts in your ignition switch, or bad switch.
Also coil gets 12 volts from the starter solinoid at startup, but lower voltage during Run.
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Old 04-18-2010, 12:54 PM   #15
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yea ignition switch is the direction im heading now. yea coil is 6 volts with key on and like 7 or 8 while cranking.
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Old 04-18-2010, 02:57 PM   #16
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Should be able to essentially hot wire by running a wire from pos battery to pos coil terminal. Then just be using the ignition switch to crank. I have done it on points ignition but I believe it would work on electronic ignition as well. At least if that worked you could try to eliminate some things.

Good luck,
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Old 04-18-2010, 04:27 PM   #17
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yea i might give that a try. on my way right now to get the battery tested. noticed it was starting slow. hooked my bronco to it and it spun much faster. now it will barely spin over. but still showing 11.7 volts so maybe a weak battery could be my whole problem.
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Old 04-18-2010, 04:35 PM   #18
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Before you get too carried away.

One of the most common things I see folks do is forget to check the starter and related components before changing coils and ignition boxes and fuel related parts or components.

The first thing you need to do is put a volt meter on the positive and negative battery posts now have someone turn the engine over, if the battery drops below 9.6 volts the engine is not turning over fast enough to fire and the ignition circuit is not getting enough voltage to fire.

If this is the case you need to isolate which component is casing the problem by load testing or voltage drop testing them, ie is it a bad starter or a bad negative or positive battery starter cable or is it a bad solenoid, or could it just be a weak or bad battery?

If it started and ran before most likely all the electrical components like the ignition box and coil are ok they don't often go bad just sitting there.
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Old 04-18-2010, 08:44 PM   #19
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yea i checked everything over. i just put a brand new battery in tonight and still no luck. i finally found a ignition test and it reads that if you get 6-9 volts on the bat terminal of the coil to replace the ignition module. which i have already done. this thing is gonna make me work hard to get it running again.
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Old 04-20-2010, 11:17 AM   #20
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found a test were it said to jumper the two black and green wires and check for voltage at the bat termial of the coil and if reading was 6-8 volts module is bad. well did it and got 6.9. so guessing module is bad. one other thing i noticed was if i unplug the module i get 12 volts to the coil. anyone got any thoughts on what i have found so far?
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