Weak spark

Reply Subscribe

Thread Tools

Search this Thread

Oct 31, 2012 | 04:06 PM

alex.g

Thread Starter

Freshman User

Joined: Apr 2006

Posts: 32

Likes: 0

From: Motherwell Scotland

Weak spark

Can anyone tell me the correct voltage of coil or suggest a replacement ignition system for my 1982 f350 its got a 351w fitted just keeps losing power to the plugs and the motor cuts out

Oct 31, 2012 | 04:32 PM

ctubutis

Moderator

Joined: Nov 2007

Posts: 22,415

Likes: 92

From: Denver Metro Area, CO

How do you know it's the coil?

The pickup in the distributor instructs the module to fire the coil at the right times. Do a google search on Duraspark diagnostics.

Oct 31, 2012 | 07:59 PM

1983F1503004x4

Fleet Mechanic

Joined: Jul 2011

Posts: 1,916

Likes: 4

If you keep losing power to the plugs and it keeps cutting out, it's probably the pickup module in the distributor like Ctubutis is suggesting. Or, it could be the ignition module if it won't fire once it's hot.

The coil gets 12 volts with the key in the CRANK position and ~7.5 volts via a ballast resistor when in the RUN position.

Oct 31, 2012 | 09:45 PM

cartmans_twin

Freshman User

Joined: May 2010

Posts: 49

Likes: 0

From: Globe/Miami, Arizona

hotwire the coil. if you can run a wire from the battery, and not cut out, that means your module is shot. I have a loose wire for just this problem. don't run that way all the time, but it'll get you home when the module won't

Oct 31, 2012 | 10:04 PM

mbailey94

New User

Joined: Sep 2012

Posts: 15

Likes: 0

get a msd ignition coil.

Nov 1, 2012 | 12:00 AM

joshofalltrades

Postmaster

Joined: Feb 2011

Posts: 3,560

Likes: 1

i would suggest you keep up on the system by maintaining it as ford produced it, not by adding a mismatched assortment of performance parts. the MSD might be good, but most of us find that the originals last 20+ years, and you can't beat that reliability.

diagnose first, then buy only the part you need

Nov 1, 2012 | 02:22 AM

TheKirbyMan

Posting Guru

Joined: Aug 2009

Posts: 2,271

Likes: 2

From: Mexia, TX

Cheapest method is to check all the wires associated with the ignition. There are some over on the fender by the ignition module, there are three that go to the distributor, and there are two that go to the coil. The wires get brittle over time and I've had them break off where they go into the factory connectors. I've had a loose wire at the coil cause a poor idle, though I don't recall noticing a loss of power at speed, at least not that I could tell.

Also check the module on the fender. Usually local auto parts stores will test them. The original Ford units are the best since they have features that the aftermarket brands likely won't (such as retarding the timing at startup for easier starting). But I ran an Autozone house brand box for a couple years with zero problems.

As far as complete replacements, I personally run an MSD 6A ignition box with the factory distributor and coil and I am very satisfied, but it's a little more expensive to get the MSD than a factory replacement. Complete MSD systems (distributor and box) aren't cheap by any means.