So the journey continues as I am trying to get my 1973 F-250 Highboy running. I have gas to the carb and all the air the 390 wants but no spark. I first noticed that I had no spark when ethier was sprayed into the carb and it dident even fire. Next I pulled 2 different spark plugs and cranked over the motor and neither one had spark. The motor will crank over fine so I know it's not the ignition system. Where do I start?

Thanks,

~Hunter

 

points or elec dizzy?

pull the cap off and see if there's any arc across the points, and if you haven't already then adjust them to where they should be

if no spark there then it's your coil or the wiring, if there is then it's the rotor/rotor button, leads, or your plugs

 

Thanks! That narrows it down for me. I will try that tonight and report what I find.

~Hunter

 

Looking for arcing across the points is not going to tell you much. The condensor is there to prevent much of the arcing in the first place; and the presence or absence of arcing doesn't really tell you much about the ignition system as a whole.

I don't understand the problem. You're saying you checked for spark with a spark plug out? How did that work exactly? Were you grounding the plug? That won't always work. The screwdriver method is much more reliable, and a spark tester is even better. Stated another way, please describe exactly why you suspect spark is to blame, rather than simply saying it is to blame.

 

I checked for spark with a plug out by grounding it to a bolt and the block and cranking the motor over. Neither of the plugs I did this too sparked. Could you please tell me about the screwdriver method?

I know that a motor needs 3 things to run, fuel, air, and spark. I know that I am getting fuel to the carb and that the intake and carb are free of obstructions. I suspect that spark is to blame because either was sprayed into the carb with the motor was cranking and the motor didn't even fire. I know that I have fuel and air thus I suspect that spark is the problem.

Thanks for the input fmc, was hoping you would chime in.

 

I understand the problem now, thanks.

A screwdriver can be used to check for spark by inserting the blade of the screwdriver into a plug wire boot, then holding the shaft of the spark plug very close to the block while the motor is cranked. This relies less on the spark plug itself making good contact against a ground that may be painted or rusted over. But the method you described should work too if the plug was truly grounded.

For now, let's assume spark is gone. Pull the negative coil wire off just enough to expose the negative coil post, while leaving the coil connected. Connect a test light from that exposed coil connection to clean, unpainted metal on the engine. Crank the engine over with the key, and the light should BLINK. Report your results.

 

What if I don't have a test light?

 

Reckon you got the intertubes and everythang, why, a test light is cheap. Maybe 2 bucks? For one o them fancy store bought jobbers. If a feller had a 12 volt bulb and some wire, he'd be set, though.

Sent from my iPhone using IB AutoGroup

 

Then get one! Come on now.

 

I got one.... With the ignition in the "ON" position the test light lights up and remains solid. With the motor cranking the test light lights up and remains solid.

 

Very good. That means the points are not triggering the coil, which could be one of the following:

1) Points physically detached from the breaker plate
2) Points burnt so severely that they cannot pass current
3) Missing breaker plate to base plate ground wire inside the distributor
4) Coil negative wire into distributor detached from points

This assumes the coil wire remained attached when you did this test. If the wire slipped off with your test light hooked up, you'll see a false "stuck ON".

 

I pulled the distributer cap and visually inspected.

1) the points ARE physically attached to the breaker plate

2) the points DID look pretty burnt

3) breaker plate to base ground plate ground wire IS intact- this is a copper "strap" correct?

4) the negative terminal wire remained connected during the test

 

Again, nice work; and yes, the ground wire is a braided strap. If you want to be sure everything is in working order, you can check the resistance from the base of the points to clean, unpainted metal on the engine (ground). The resistance should be no more than that of your meter leads. That will prove out the primary side ground path.

If that checks out, and you've verified that the rotor is turning when the engine cranks, then install and gap new points and install a new condensor.

 

Thanks, just to let you know I am learning as we go, I have no experience with electrical whatsoever. How can I check the resistance of my multimeter leads? With my multimeter on the 200 ohm setting and touching the leads together it reads 1.1 is this my lead resistance? Can't thank you enough Fmc, your the best! Rep comin your way.

 

No problem; and yes, you have the correct idea. You measure the resistance of the leads shorted together before taking a measurement so that you can understand how much the circuit under test is contributing (sort of like taring a scale). Your meter probably has a "20" scale for better accuracy.

In this case, you're not looking for too much accuracy, just a quick yes/no answer that things are truly hooked up and there's nothing catastrophic going on. You'll see a finite resistance because of the relatively poor "connection" the leads will make to the two surfaces. But if the leads are pressed well into two clean surfaces, then the meter should indeed read that which is equal to your lead resistance.