No Start Problem, Has Spark and Fuel

[stuart 13]

Need some help diagnosing an electrical problem.  To begin it's a 1969 Mach 1, 351 4V with factory tach and running Pertronix III and Pertronix Ignitor coil.  Last weekend it cranked up fine and ran briefly, then died.  After that when turning the motor over it would catch and fire once, then die. I'm getting the Alternator light in the dash, but tachometer isn't moving.  Carburetor, fuel pump, battery, starter, and solenoid all checked out ok.    I swapped back to Ford coil and points and no fix to problem.  I pulled the plug from back of ignition switch and found what appeared to be a short where the black w/green and dark pink connect at the plug. Installed a replacement pigtail and no fix.  I'd like to fix this myself and not have to drag her to a repair shop.

Should I be suspecting a fault in the tach, or start tracking down a short or burned fusible link somewhere in the harness?

thanks,

Stu

[LoneWolf2U 136]

Yes bypass the tach to verify its not the problem of grounding out the ign circuit. 

Also check that you have voltage at the + side of coil with ign switch in on position.

[stuart 13]

Thanks, I’ll try the bypass first.  Can I just unplug the tach from the harness and jump between the two pins on the connector?

[LoneWolf2U 136]

IIRC the harness side is a male/female connector, You should be able to unplug the tach and plug the harness wires togeather for test.

[Mach1 Driver 560]

Well you already said you're getting spark so its probably not electrical. Are you getting 12V to the coil when starting? If you have a VOM connect one side to chassis and the other to the Bat. side of the coil. See below for the expected voltages. Make sure your battery is topped off. It could be a timing issue, a bad capacitor or point gap.

BTW, there are no fusible links on a 69, they started using them in 70. This schematic shows you how it works:

[LoneWolf2U 136]

It may be only getting spark while cranking the starter, power to the coil is coming from the sol on the fender.

Lack of coil power in run is from the tach or resistor wire or key. process of elimination  using the wiring diagram.

[danno 128]

You might try putting a jumper wire between the battery and the high side of the coil.  Do this only when you know it does not work normally, and then do it for only a few seconds.  Doing this will bypass the ignition switch, tachometer, resistor wire, and all dash wires.  I have tried this and it proved my fault was in my coil.  In my case, as soon as the coil warmed up, it would stop working.  I tried my trick when the coil was cold and it showed that it worked.  I connected the coil back up to the engine harness, and started the car.  It ran for 8 minutes and died.  I then connected 12 volts right to the coil, and this time it would not run.   I replaced the coil, and it has been fine for years. 

So the next time your stops working, put a wire between your battery and the coil, and see if that works.  You need to do it quickly, when the coil is still warm, to confirm that is the problem.   

This might not be it for you, I am just passing on what I found in mine.   The coils stop working after they warm up. 

[ashleesmach1 28]

On 1/14/2020 at 8:10 PM, Mach1 Driver said:

Well you already said you're getting spark so its probably not electrical. Are you getting 12V to the coil when starting? If you have a VOM connect one side to chassis and the other to the Bat. side of the coil. See below for the expected voltages. Make sure your battery is topped off. It could be a timing issue, a bad capacitor or point gap.

BTW, there are no fusible links on a 69, they started using them in 70. This schematic shows you how it works:

your schematic shows there is a resister wire at 1.66 ohms. A lot of people call this a fusible link. I believe its the pink wire 

[Mach1 Driver 560]

4 hours ago, ashleesmach1 said:

your schematic shows there is a resister wire at 1.66 ohms. A lot of people call this a fusible link. I believe its the pink wire 

Correct, it is a pink resistor wire. However, It is not a fusible link and I've never heard it referred to as one. Fuse links are intended to burn through in high current situations and act as fuses, the pink resistor wire does not have that function. Fuse links are short pieces of wire that are usually sized about two wire gauges smaller than the wire they are connected to. Ford didn't start using fuse links until 1970.  I believe Chrysler products still used a ballast resistor at this time, instead of a resistor wire. GM and Ford, in a cost cutting move decided to use the wire they needed to connect to the coil anyway, and deleted the ballast resistor. The length of the pink resistor wire is long enough so that it dissipates the heat that would normally be coming out of the ballast resistor as it drops the voltage. The dropped voltage is dissipated as heat.

The circuit operates in this way: the key is turned, the path is closed through ignition switch "B" and out "S" through the neutral safety switch to the starter solenoid "S". The solenoid closes, giving power to the starter motor through the top contact and out through solenoid terminal "I". This bypasses the pink resistor wire and gives you a full 12 volts to the coil to allow for faster starting. As soon as the key is released the path from ignition switch "S" opens, the solenoid turns off, which shuts down the starter motor, and opens "I". The engine then runs normally out through ignition switch terminal "C", through the tach if you have one, otherwise this path is connected directly to the pink resistor wire. This drops the voltage to the coil and points so they last longer.

[ashleesmach1 28]

cool!

[dcm0123 15]

On 1/16/2020 at 11:01 PM, danno said:

You might try putting a jumper wire between the battery and the high side of the coil.  Do this only when you know it does not work normally, and then do it for only a few seconds.  Doing this will bypass the ignition switch, tachometer, resistor wire, and all dash wires.  I have tried this and it proved my fault was in my coil.  In my case, as soon as the coil warmed up, it would stop working.  I tried my trick when the coil was cold and it showed that it worked.  I connected the coil back up to the engine harness, and started the car.  It ran for 8 minutes and died.  I then connected 12 volts right to the coil, and this time it would not run.   I replaced the coil, and it has been fine for years. 

So the next time your stops working, put a wire between your battery and the coil, and see if that works.  You need to do it quickly, when the coil is still warm, to confirm that is the problem.   

This might not be it for you, I am just passing on what I found in mine.   The coils stop working after they warm up. 

Do what he says but do not leave it connected for more than a couple of minutes because you will bypass the resistor. This bypasses your entire electrical system. If it starts then you need to figure out which part in the electrical system is bad.

Pull the spark plug wire and check to see if there is spark at the wire. Connect it to a plug, lay it on the manifold so it is grounded good and have someone crank the motor so you can look for spark..

Make sure the coil case is grounded. and the ground inside the distributer is connected properly.

 

[stuart 13]

Gentlemen, et al:

Thanks for your assistance with this electrical issue.  The problem turned out to be an inop tachometer which is now on it's way to the Tach Man for repair.

Stu