Ignition Coil failure - Ford Truck Enthusiasts Forums

1973 - 1979 F-100 & Larger F-Series Trucks Discuss the Dentsides Ford Truck

Ignition Coil failure

Thread Tools Search this Thread
Old 08-13-2007, 11:10 AM
BottomFeeder BottomFeeder is offline
Senior User
Thread Starter
Join Date: May 2006
Posts: 114
BottomFeeder is starting off with a positive reputation.
Ignition Coil failure

How do ignition coils fail? Do they slowly lose their spark as they age?

I've got '78 F250 with a 351M and it seems to be slightly missing. Sometimes the whole engine shakes and trembles with the oscillation and shakes the whole truck.

I've rebuilt the carb (it needed it badly), replaced the plugs and wires. But, I'm not sure about the strength of the spark.

A week ago, the truck died on me. I thought it was the fuel, as it was rather low. But even starter fluid wouldn't catch. We jiggled the ingition coil plug wires and it eventually started up.

I'm about to go on a 1200 mile round trip in this truck, through some harsh terrain, and I'd like for it to be as reliable as possible.

Should I swap out the ignition coil just for good measure, or is that a waste of time?
Reply With Quote
Old 08-13-2007, 11:13 AM
Mil1ion Mil1ion is offline
New User
Join Date: Jan 2008
Posts: 0
Mil1ion is starting off with a positive reputation.
Electrical forum . not 73-79 related

They break down from constant temperature fluxuation like any transformer.

This is electrical tech
Reply With Quote
Old 08-13-2007, 07:38 PM
rusty7983's Avatar
rusty7983 rusty7983 is offline
Elder User
Join Date: Feb 2007
Location: hohenwald, tn
Posts: 796
rusty7983 is starting off with a positive reputation.
you sure its the coil? more likely the control module or dist. pickup. both can do the same thing you said yours did. these coils rarely don't work. the spark they produce starts to weaken over the years. but it should still work. the wires on the pickup break often. as the advance moves the wire inside breaks contact. the modules are also known to be bad, most parts stores check them. but they often fail when they get warm and not when they are cold. sometimes its hit or miss where they don't work. wait till it happens again, even if you leave it idling in your yard.
Reply With Quote
Old 08-15-2007, 04:28 PM
bigperm2 bigperm2 is offline
Senior User
Join Date: Jan 2004
Location: denver
Posts: 367
bigperm2 is starting off with a positive reputation.
Does the coil get hot? I have been fighting with the coil on my bronco for a while, it gets super hot and quits working. After it cools down a little, it will run again only for a few minutes. Depending on your ignition system, you should have a ballast resistor or resistance wire. Check your voltage at the coil while it is running, it should be around 9 volts.
Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
1973 F-100 390 idles fine misses at rpm olddudeoldford 1973 - 1979 F-100 & Larger F-Series Trucks 9 01-11-2015 05:00 AM
Ignition Switch Wiring +12v jfarcas 1973 - 1979 F-100 & Larger F-Series Trucks 8 11-29-2007 09:19 AM
What spark plugs do you guys recommend? 68murc Big Block V8 - 385 Series (6.1/370, 7.0/429, 7.5/460) 8 03-24-2007 08:43 AM
Weak to no spark from ignition coil Gov 1978 - 1996 Big Bronco 5 01-17-2005 04:28 PM
Swapped 351M for 460, no spark. What's this do? AMiller320 335 Series- 5.8/351M, 6.6/400, 351 Cleveland 9 10-23-2002 12:49 PM

Go Back   Ford Truck Enthusiasts Forums >

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

All times are GMT -5. The time now is 02:37 PM.