No spark... How to isolate the problem?
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New User
Joined: Feb 2004
Posts: 12
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From: Tucson, AZ
No spark... How to isolate the problem?
Hi all,
After some tinkering, the 1978 F250 (460) that I recently aquired still has no spark. I think we've already established that rewiring it completely is a bit premature. So then: What exactly should I check (and in what order) to systematically eliminate any false issues and to isolate what is the actual problem(s).
The truck has not run since its been in my possession, so it really could be anything. I have gotten it to crank after replacing the starter relay and some cables. Please help, my technical knowledge is as limited as my desire to get this thing running is big. And thanks to those who have already helped... this sight is awesome!
After some tinkering, the 1978 F250 (460) that I recently aquired still has no spark. I think we've already established that rewiring it completely is a bit premature. So then: What exactly should I check (and in what order) to systematically eliminate any false issues and to isolate what is the actual problem(s).
The truck has not run since its been in my possession, so it really could be anything. I have gotten it to crank after replacing the starter relay and some cables. Please help, my technical knowledge is as limited as my desire to get this thing running is big. And thanks to those who have already helped... this sight is awesome!
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Joined: Jan 2008
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12V Power from starter solenoid to ignition switch.
12 V Power from ignition switch to coil.
12V Power from ignition switch to control module
Power from control module to Coil
High voltage power from coil to distributor cap
Signal power from pickup coil inside distributor cap
High voltage from coil to distributor cap
High voltage from Distributor cap to spark plug wires.
High Voltage from Plug Wires to Plugs
12 V Power from ignition switch to coil.
12V Power from ignition switch to control module
Power from control module to Coil
High voltage power from coil to distributor cap
Signal power from pickup coil inside distributor cap
High voltage from coil to distributor cap
High voltage from Distributor cap to spark plug wires.
High Voltage from Plug Wires to Plugs
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New User
Joined: Feb 2004
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From: Tucson, AZ
Alright, thanks Mil1ion for the speedy reply! I think we can work backwards a little bit here. I checked for conductivity in the all the wires from the coil to the plug and everything on that end seems fine. Also, interestingly, I'm getting 12v on all the leads on the starter relay without turning the ignition on 
. This is about when i stopped figuring I must be doing something wrong. Should I not be checking each terminal with one lead of the voltmeter on the neg and one on the terminal thats being tested?
. This is about when i stopped figuring I must be doing something wrong. Should I not be checking each terminal with one lead of the voltmeter on the neg and one on the terminal thats being tested?
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Joined: Jan 2008
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with a VO Meter.
Black goes to ground > the frame or body that isn't separated by rubber or non-conductive
Red only touches the terminals.
On a starter solenoid :
I terminal for ignition start 12V to coil
S terminal for power to trip relay for starter motor
Large terminal rear = for full power to drive starter motor.
Large terminal front = to power the complete vehicle & its circuits.
Black goes to ground > the frame or body that isn't separated by rubber or non-conductive
Red only touches the terminals.
On a starter solenoid :
I terminal for ignition start 12V to coil
S terminal for power to trip relay for starter motor
Large terminal rear = for full power to drive starter motor.
Large terminal front = to power the complete vehicle & its circuits.
Senior User
Joined: May 2003
Posts: 455
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From: Alaska
I'm going to assume you have the duraspark ignition with the control box on the left fender well,
It is my experience that the probabilities are:
1, loose conections, check all connections and plugs, there are several.
2, control module, difficult to test, exchange with a known good one.
3, coil, also difficult to test.
4, pick-up coil inside distributor, the constant action of the vacuum advance flexes the wires inside the distributor and they can break, also check the ground, it is one of the pick-up coil mounting screws.
Hope this helps, FSC
It is my experience that the probabilities are:
1, loose conections, check all connections and plugs, there are several.
2, control module, difficult to test, exchange with a known good one.
3, coil, also difficult to test.
4, pick-up coil inside distributor, the constant action of the vacuum advance flexes the wires inside the distributor and they can break, also check the ground, it is one of the pick-up coil mounting screws.
Hope this helps, FSC
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Joined: Apr 2004
Posts: 409
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Check power to the coil @ key on
Check power to the coil @ cranking
Check for pulsing power on the other side of coil @ cranking
No pulse? Bad pickup coil or wiring. Good pulse/ no spark? Bad module or wiring, or coil.
Check power to the coil @ cranking
Check for pulsing power on the other side of coil @ cranking
No pulse? Bad pickup coil or wiring. Good pulse/ no spark? Bad module or wiring, or coil.