Ignition Problems
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4wd Low
Joined: Mar 2015
Posts: 13
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Ignition Problems
Hello there!! So I've got quite the problem on my hands. My '79 isn't starting due to spark problems. I'm getting spark from the coil in the "run" position on the key, but when I switch over to cranking the spark stops.
The things I've done so far are
-New Distributor cap
-New Rotor
these were in need of being replaced
and while I was at Napa I picked up and replaced
New Wires
New Coil
New Module
I'm working with all new components and it hasn't seemed to cure the problem. I've done all the testing I know how to do, and I'm quite frankly pretty lost on why this is happening. Any help would be much appreciated!!! Thanks in advance!!
-Chester
The things I've done so far are
-New Distributor cap
-New Rotor
these were in need of being replaced
and while I was at Napa I picked up and replaced
New Wires
New Coil
New Module
I'm working with all new components and it hasn't seemed to cure the problem. I've done all the testing I know how to do, and I'm quite frankly pretty lost on why this is happening. Any help would be much appreciated!!! Thanks in advance!!
-Chester
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4wd Low
Joined: Mar 2015
Posts: 13
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It started acting odd bout 3 weeks ago...thought is was fuel related. Rebuilt the carb, saw I had enough fuel, but it still would die on me after having it run about 30 mins. so I started checking into ignition.
Elder User
Joined: Sep 2014
Posts: 862
Likes: 7
From: like subarctic, brrr man!
What's the Voltage at the coil Positive + terminal?
Check this with Ignition switch in Run and Start.
During Run, it should be around 8volts (Voltage goes through a Resistor wire which runs from near the fuse block to around middle of the dash).
During Start, it should be full battery voltage (~12 volts). This voltage is fed from the Start Solenoid/Relay I terminal.
I suspect it's not this, but it's a start in diagnosis! Check the triggering wheel and check for continuity. One of those wires should be ground, but two go through the magnetic pickup and should have continuity.
Check this with Ignition switch in Run and Start.
During Run, it should be around 8volts (Voltage goes through a Resistor wire which runs from near the fuse block to around middle of the dash).
During Start, it should be full battery voltage (~12 volts). This voltage is fed from the Start Solenoid/Relay I terminal.
I suspect it's not this, but it's a start in diagnosis! Check the triggering wheel and check for continuity. One of those wires should be ground, but two go through the magnetic pickup and should have continuity.
Thread Starter
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4wd Low
Joined: Mar 2015
Posts: 13
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you're right...I got to start some where!! I'll have to check the voltage on the coil again. I'll relay what I find to you tomorrow...the school shop just closed for the day and I can't get back to the truck till bout 7:00 in the A.M.
Also, How do you check the ignition switch? After Mountain Dewd mentioned that I removed it....there are quite a few terminals in there and I don't know how to go about it.
Also, How do you check the ignition switch? After Mountain Dewd mentioned that I removed it....there are quite a few terminals in there and I don't know how to go about it.
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Elder User
Joined: Sep 2014
Posts: 862
Likes: 7
From: like subarctic, brrr man!
I mentioned the ignition switch to indicate it's position... Maybe double check all the wires going to it, by pushing them into the switch. Maybe one's loose and not making contact?
Looking at the '78 and '79 Wiring schematics, the reluctor or trigger thing in the distributor has three wires.
Bk-Gr (Black-Green) is ground, check it's continuity to the distributor body. it should be 0 Ohms.
Also, check continuity to the other wires, and it should be infinite resistance (No Continuity). If it shows something it's shorting out and should be replaced.
O-Y (Orange-Yellow?) and P-Bl (Pink or Purple-Blue?) are the wires to the triggering thing. It should have continuity, but un-sure what it's ohms are.... but it should show something. If there isn't continuity, then there is an open in this and should be replaced.
A Faulty Reluctor or trigger might explain the symptoms you have, spark but no engine running... because the Ignition Module doesn't know when to spark the coil.
Looking at the '78 and '79 Wiring schematics, the reluctor or trigger thing in the distributor has three wires.
Bk-Gr (Black-Green) is ground, check it's continuity to the distributor body. it should be 0 Ohms.
Also, check continuity to the other wires, and it should be infinite resistance (No Continuity). If it shows something it's shorting out and should be replaced.
O-Y (Orange-Yellow?) and P-Bl (Pink or Purple-Blue?) are the wires to the triggering thing. It should have continuity, but un-sure what it's ohms are.... but it should show something. If there isn't continuity, then there is an open in this and should be replaced.
A Faulty Reluctor or trigger might explain the symptoms you have, spark but no engine running... because the Ignition Module doesn't know when to spark the coil.
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Senior User
Joined: Dec 2012
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From: Wildwood, Mo
Our 79 Bronco 351M gave intermittent starting trouble for a long time. Once I replaced the ignition module and it worked for 2 weeks so I threw out the old one. Then the problem came back! It turned out to be the sensor or whatever in the distributor. I couldn't gracefully get the distributor out and broke it. A rebuilt distributor fixed the problem and that was years ago, so it is fixed. Patrick
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4wd Low
Joined: Mar 2015
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Oh ok!! I'll take a look at the reluctor in the distributor tomorrow ZarK-eh...Should I be looking for anything else wrong with it aside from the wire connections and continuity??
I'm hoping all it is is that piece in there...and that it'll last a good long time once replaced as well!! haha!!
I checked my spark by popping off the coil to dist cap wire and sticking a long screwdriver in the end. Set it next to good ground metal, and played with the key. Saw only one spark when initially put in the "run" position, spark stopped in cranking position, then one spark after key returned to the "run" position.
I'm hoping all it is is that piece in there...and that it'll last a good long time once replaced as well!! haha!!
I checked my spark by popping off the coil to dist cap wire and sticking a long screwdriver in the end. Set it next to good ground metal, and played with the key. Saw only one spark when initially put in the "run" position, spark stopped in cranking position, then one spark after key returned to the "run" position.
Elder User
Joined: Sep 2014
Posts: 862
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From: like subarctic, brrr man!
I'm handy with a multi-meter, and not sure what else to check in the distributor.
I replaced mine with a '96 distributor for my EFI upgrade and ditched all the old complicated advance stuff.
edit: not related but fyi, the '96 distributors are straight up solid shaft without advance mechanisms. The timing curve is set on a graph in the efi computer. Really complex solution to get an easy to tune setup lol!
I replaced mine with a '96 distributor for my EFI upgrade and ditched all the old complicated advance stuff.
edit: not related but fyi, the '96 distributors are straight up solid shaft without advance mechanisms. The timing curve is set on a graph in the efi computer. Really complex solution to get an easy to tune setup lol!
Last edited by ZarK-eh; Mar 2, 2016 at 11:52 PM. Reason: see above FYI for why I did '96 distributor
Thread Starter
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4wd Low
Joined: Mar 2015
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Alrighty...So I've done some poking around today. I'm thinking that it is a heat problem somewhere. When I went to turn it over it started right up!!! no hesitation at all. checked the coil again with that screwdriver method I explained earlier and I was getting spark when I needed it. So I'm thinking the problem is somewhere either at or before the coil and is being caused by heat. I did have the truck running a bit yesterday...till it got to operating temp, then the no spark during cranking problem was found....any thoughts?
Regular User
Joined: Sep 2014
Posts: 1,798
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From: Bathurst, New Brunswick
You replaced your ICM? Are you sure you got the correct one? They all look very much alike except for the colour of the plastic grommet the wires come out of. Make sure your new one has the same colour (blue, black, green). Good luck.