1978 F-150 351M CRANKS BUT NO SPARK.....HELP!
#1
1978 F-150 351M CRANKS BUT NO SPARK.....HELP!
I have had my faithful 78 F150 since the day I drove it off the lot with 11 miles on it. Now after 40 years of NEVER a problem, 'trucky' will not start. Cranks fine but no start. I have replaced ignition switch, control module, coil, distributor, cap, rotor, plugs, starter, fuel pump and carb!! NO SPARK! I even went to the mobile mechanic site and set up appointment and NOT ONE person is familiar with ANYTHING pre 1990!! Can any member PLEASE help me? I am retiring this year and was going to have 'trucky' spiffed up for our retirement together. This is so frustrating.......3 months of internet searches, phone calls, and Ubering.
Thanks.
Thanks.
#2
Welcome to FTE!
It's gotta be in your wiring somewhere, because you've replaced everything I can think of. The wiring on mid '70s to mid '80s Ford ignitions does have something of a history of trouble.
Probably most common would be insulation which has shrunk back/away from connectors, exposing the copper conductor. I suspect oil exposure is the culprit here.
Another phenomenon is insulation which dries out and crumbles, flaking away and again exposing that conductor. Mid '80s Fox bodies are good for that, but I've heard of it on other Fords as well.
Not sure of the proper troubleshooting for DuraSpark, (I've never had to do any in well over 200,000 miles in DS vehicles) but I might check to see if the ignition won't spark in both "Start" and "Run" modes. The only part which you didn't mention is the Fender Mounted Starter Relay/solenoid, but I don't know how it could cause a no-spark - other than maybe not energizing the DS box during cranking/Start mode?
There are also the 'main' harness groups of wires which pass through the firewall at the top driver/left side corner. There are several different connectors right there, (mostly two or three wires each) and one of them could've developed some corrosion or something. The one for the brake warning lamp gave me some trouble when I first had my truck.
And check your fuses. You didn't mention that. And even if a fuse is good/unblown, it could still be not passing current due to corrosion at the fuse holders/contacts.
If by some miracle you managed to hold onto all of the parts you replaced, you might want to put them all back on.
It's gotta be in your wiring somewhere, because you've replaced everything I can think of. The wiring on mid '70s to mid '80s Ford ignitions does have something of a history of trouble.
Probably most common would be insulation which has shrunk back/away from connectors, exposing the copper conductor. I suspect oil exposure is the culprit here.
Another phenomenon is insulation which dries out and crumbles, flaking away and again exposing that conductor. Mid '80s Fox bodies are good for that, but I've heard of it on other Fords as well.
Not sure of the proper troubleshooting for DuraSpark, (I've never had to do any in well over 200,000 miles in DS vehicles) but I might check to see if the ignition won't spark in both "Start" and "Run" modes. The only part which you didn't mention is the Fender Mounted Starter Relay/solenoid, but I don't know how it could cause a no-spark - other than maybe not energizing the DS box during cranking/Start mode?
There are also the 'main' harness groups of wires which pass through the firewall at the top driver/left side corner. There are several different connectors right there, (mostly two or three wires each) and one of them could've developed some corrosion or something. The one for the brake warning lamp gave me some trouble when I first had my truck.
And check your fuses. You didn't mention that. And even if a fuse is good/unblown, it could still be not passing current due to corrosion at the fuse holders/contacts.
If by some miracle you managed to hold onto all of the parts you replaced, you might want to put them all back on.
#4
I'm supposing you checked for spark in the usual way....coil wire to a ground....spark plug to ground whilst cranking her over, and you get nothing?
If you did that with no spark/start, here's a test for voltage to the coil. You'll be checking the ballast resistor wire ------Key ON, Engine OFF. Measure the voltage from the coil (+) to ground. (If you have the stock horseshoe connector be sure you have good connections). You want to see ~ 5 VDC - 8 VDC.
These puppies have been known to go south....especially after 40 years.
If you have a quick start then she croaks on you, well there's a different test for that.
So, whatcha got?
If you did that with no spark/start, here's a test for voltage to the coil. You'll be checking the ballast resistor wire ------Key ON, Engine OFF. Measure the voltage from the coil (+) to ground. (If you have the stock horseshoe connector be sure you have good connections). You want to see ~ 5 VDC - 8 VDC.
These puppies have been known to go south....especially after 40 years.
If you have a quick start then she croaks on you, well there's a different test for that.
So, whatcha got?
#5
Join Date: Aug 2016
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40 trouble free years ! Brilliant !
Did you replace those parts subsequent to NO SPARK, or simply over time ?
No mention of HT cable replacement.
You could also check the resistance in the HT cable from the dizzy to the coil.
Basically this will be a process of elimination until you find the fault, using the tests already mentioned, but it shouldn't be too difficult.
Determine the ignition wires circuit only, and check each one visually and with a multimeter.
You will find the fault and you will fix it.
Did you replace those parts subsequent to NO SPARK, or simply over time ?
No mention of HT cable replacement.
You could also check the resistance in the HT cable from the dizzy to the coil.
Basically this will be a process of elimination until you find the fault, using the tests already mentioned, but it shouldn't be too difficult.
Determine the ignition wires circuit only, and check each one visually and with a multimeter.
You will find the fault and you will fix it.
#7
Haven't thought the whole thing through yet, but wanted to ask you that if you still have your original '78 ignition control module, if you could get a couple of good shots of it for me!
Been hoping to see another original just to check it out and compare.
Now I'll go back and re-read what's been said to see if I can add anything worthwhile. Just wanted to get that other bit out while I was thinking about it.
Thanks!
Paul
Been hoping to see another original just to check it out and compare.
Now I'll go back and re-read what's been said to see if I can add anything worthwhile. Just wanted to get that other bit out while I was thinking about it.
Thanks!
Paul
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#8
#9
"Proper resistance"......on what? From where to where? Are you referring to the coil? What is "proper resistance?"
Fusable link...you should have one going to the (+) side of the starter solenoid, from the alternator. It's ORANGE in color.
Test - Do you have lights?
#10
Not sure why you had to try four coils, unless you had them lying around. Hate to think you bought four new ones.
You can test coils with both resistance and with a temporary jumper wires to see if it can produce spark independent of the ignition box (Duraspark Module) or ignition switch.
Ford trucks have had fusible links at least since the early sixties as far as I know, but I'm not aware of one just for the ignition circuit. If your main link was burned out you would have lost all power to the cab, and therefore the ability to crank the engine.
Good call on the mechanic at least for giving it a shot. But unless there is another one, this is not the issue. And if you can get a voltage reading at the coil, then there is no fusible link failure in that circuit anyway.
As FB said, were you measuring resistance for the coil only, or on the coil's positive wire?
When the vehicle first starts, you may actually have 12v or slightly less for a little while until the resistor wire warms fully. You're not going to get this full warming however, if the engine is not running. So your voltage readings will be high for the initial checking sometimes.
Another result is if you've had the key on for a minute or two with the distributor in just the right position, or if you ground the negative side of the coil with the key on, you should see the voltage lower to the mentioned 6-9 volts at some point fairly quickly.
My experience has been the opposite of Filthy Beasts however, and I have run factory Ford (and some GM too actually) ignition coils on a full 12v jumpered directly from the battery for extended periods of time with no apparent damage to the coils. I ran my original Bronco coil from '71 for a couple of months that way in fact, until I fixed the dead circuit feeding it previously. Granted, this was done typically for less than an hour at a time, a couple of times a day. Then the wire was disconnected to kill the engine. I'm just saying I've never had a coil burn out instantly because I ran 12v and got it hot.
But that doesn't mean it can't happen. Especially with new stuff!
So you put new parts on it, but "new" does not always mean "good" anymore, so you may have to go to manually checking to see if you can find another culprit.
For instance, can you test your Duraspark harness connections to make sure you're getting 12v to the 2-wire connector at the box? Are you running a "blue grommet" control module? This is the plastic strain relief color where the wires exit the module. If it's blue, it should have some variation of Red and White wires, or Red and Blue wires, or something along those lines. At least one of them should have battery voltage when the key is in RUN. (but not ACC) so that's easy to check.
If you have voltage to the coil now (no matter what the reading) you can place the coil ht-lead near a decent grounded surface and turn the key to RUN. Then with a small jumper wire you can ground out the negative side of the coil and hear/see a spark if it produces one. Each time you remove and replace this ground wire, you should get a spark. No matter how quickly you do it, you're going to get a spark if the coil is working.
One last thing I'm not sure I mentioned the last time. If you still have your radio noise suppressor on the side of the coil, disconnect it. If it fails and goes to permanent grounding condition, you will never get a spark. So disconnect it and try things again.
It'd be really nice if it was that simple, but we're not there yet.
Good luck.
Paul
You can test coils with both resistance and with a temporary jumper wires to see if it can produce spark independent of the ignition box (Duraspark Module) or ignition switch.
Ford trucks have had fusible links at least since the early sixties as far as I know, but I'm not aware of one just for the ignition circuit. If your main link was burned out you would have lost all power to the cab, and therefore the ability to crank the engine.
Good call on the mechanic at least for giving it a shot. But unless there is another one, this is not the issue. And if you can get a voltage reading at the coil, then there is no fusible link failure in that circuit anyway.
As FB said, were you measuring resistance for the coil only, or on the coil's positive wire?
When the vehicle first starts, you may actually have 12v or slightly less for a little while until the resistor wire warms fully. You're not going to get this full warming however, if the engine is not running. So your voltage readings will be high for the initial checking sometimes.
Another result is if you've had the key on for a minute or two with the distributor in just the right position, or if you ground the negative side of the coil with the key on, you should see the voltage lower to the mentioned 6-9 volts at some point fairly quickly.
My experience has been the opposite of Filthy Beasts however, and I have run factory Ford (and some GM too actually) ignition coils on a full 12v jumpered directly from the battery for extended periods of time with no apparent damage to the coils. I ran my original Bronco coil from '71 for a couple of months that way in fact, until I fixed the dead circuit feeding it previously. Granted, this was done typically for less than an hour at a time, a couple of times a day. Then the wire was disconnected to kill the engine. I'm just saying I've never had a coil burn out instantly because I ran 12v and got it hot.
But that doesn't mean it can't happen. Especially with new stuff!
So you put new parts on it, but "new" does not always mean "good" anymore, so you may have to go to manually checking to see if you can find another culprit.
For instance, can you test your Duraspark harness connections to make sure you're getting 12v to the 2-wire connector at the box? Are you running a "blue grommet" control module? This is the plastic strain relief color where the wires exit the module. If it's blue, it should have some variation of Red and White wires, or Red and Blue wires, or something along those lines. At least one of them should have battery voltage when the key is in RUN. (but not ACC) so that's easy to check.
If you have voltage to the coil now (no matter what the reading) you can place the coil ht-lead near a decent grounded surface and turn the key to RUN. Then with a small jumper wire you can ground out the negative side of the coil and hear/see a spark if it produces one. Each time you remove and replace this ground wire, you should get a spark. No matter how quickly you do it, you're going to get a spark if the coil is working.
One last thing I'm not sure I mentioned the last time. If you still have your radio noise suppressor on the side of the coil, disconnect it. If it fails and goes to permanent grounding condition, you will never get a spark. So disconnect it and try things again.
It'd be really nice if it was that simple, but we're not there yet.
Good luck.
Paul
#11
I'd like to echo Paul's comment that "new" doesn't necessarily mean "good". Try to confirm component performance independent of the entire "system".
This may not help much, but just in case, I'd like to mention that in January 1980, Ford issued a 23 page service news bulletin, number 80-19, titled "Diagnosis of solid state ignition systems for Ford cars and trucks (1974-1980)". It provided a methodical procedure to analyze the Duraspark systems to reveal pesky shortfalls. If you have access to this publication, reading it may provide more insight to your situation. It did require the use of a voltmeter, ohmmeter, tachometer, and oscilloscope.
If you went for 40 years without any ignition problems, you were in a minority. Apparently, your good luck just ran out.
Try to establish correct performance of the primary side of the ignition system first. While I see that you've replaced it, let me say that the module has been traditionally a place of frustrating shortfalls. But since the shortfall made itself known during a "cold" vehicle time, the module may not be involved. They more often fail during elevated temperatures.
The members have provided many suggestions. You'll just have to "go through" everything in a methodical manner. There is an answer to this mystery. I doubt that the Twilight Zone is involved.
When you find it, please let us know.
Best wishes.
This may not help much, but just in case, I'd like to mention that in January 1980, Ford issued a 23 page service news bulletin, number 80-19, titled "Diagnosis of solid state ignition systems for Ford cars and trucks (1974-1980)". It provided a methodical procedure to analyze the Duraspark systems to reveal pesky shortfalls. If you have access to this publication, reading it may provide more insight to your situation. It did require the use of a voltmeter, ohmmeter, tachometer, and oscilloscope.
If you went for 40 years without any ignition problems, you were in a minority. Apparently, your good luck just ran out.
Try to establish correct performance of the primary side of the ignition system first. While I see that you've replaced it, let me say that the module has been traditionally a place of frustrating shortfalls. But since the shortfall made itself known during a "cold" vehicle time, the module may not be involved. They more often fail during elevated temperatures.
The members have provided many suggestions. You'll just have to "go through" everything in a methodical manner. There is an answer to this mystery. I doubt that the Twilight Zone is involved.
When you find it, please let us know.
Best wishes.
#12
X2! LOL at 21st century 'quality...'
Never heard of this one, but it's good to know.
And to regurgitate from above, you do not want a full 12V+ going to the coil when the engine is running, or when the key is in the "Run" position. Can you grab a volt meter and check that again? Can you post up some pics of your wiring?
The coil should only see the full 12 volts when the starter is cranking. This is accomplished by the "I" lug on your Fender Mounted Starter Relay/solenoid, next to the "S" lug with the red/blue wire from your ignition switch. That lug sends 12V to the coil. There is a diode or something in the solenoid to prevent back feeding from "I" to "S," so if you connect the wire which should go to "I" instead to the "S" circuit, you will experience starter run-on problems. AMHIK - ask me how I know - am hick...
One last thing I'm not sure I mentioned the last time. If you still have your radio noise suppressor on the side of the coil, disconnect it. If it fails and goes to permanent grounding condition, you will never get a spark. So disconnect it and try things again.
It'd be really nice if it was that simple, but we're not there yet.
It'd be really nice if it was that simple, but we're not there yet.
And to regurgitate from above, you do not want a full 12V+ going to the coil when the engine is running, or when the key is in the "Run" position. Can you grab a volt meter and check that again? Can you post up some pics of your wiring?
The coil should only see the full 12 volts when the starter is cranking. This is accomplished by the "I" lug on your Fender Mounted Starter Relay/solenoid, next to the "S" lug with the red/blue wire from your ignition switch. That lug sends 12V to the coil. There is a diode or something in the solenoid to prevent back feeding from "I" to "S," so if you connect the wire which should go to "I" instead to the "S" circuit, you will experience starter run-on problems. AMHIK - ask me how I know - am hick...
#13
in addition to the troubleshooting steps above, take the distributor cap off and make sure the rotor turns when you crank the engine. The pickup coil in the distributor is what triggers the ignition module to make the coil spark...
These trucks are pretty simple, even a newer mechanic "should" be able to perform some basic trouble shooting to figure it out...
These trucks are pretty simple, even a newer mechanic "should" be able to perform some basic trouble shooting to figure it out...
#14
The Dura Spark II is pretty bullet proof.
Testing sequence. for a totoally unknown no spark fault.
Step 1. Remove Dist cap Crank engine ensure Rotor is turning.
Step 2. Put igntion switch to run. Check for Batt voltage at red wire at Ignition module reduced voltage 6-8V at (batt) red wire on coil. If no voltage is seen at either location repair circuit (wiring, ignition switch ballast resistor)
Step 3 Remove Starter feed from fender Starter relay (optonal) This just keeps you from cranking the engine over while testing and removes the possibility of getting stuff hung up in the fan. If you leave the starter feed hooked up. Put ignition switch to start Check for batt voltage on the white wire at ignition module and the (batt) red wire on coil. If no voltage is seen at either location repair circuit (wiring ignition switch or start relay)
Step 4 Unplug the pick up coil at the dist measure resistance with the Ignition switch off Measure resistance between orange and purple wire on the coil side if the resistance is more than 850 ohms or less than 790 ohms pick up coil is failed replace pick up coil.
Step 5 Measure continuity to ground on the black wire on the dist side of above connector. If readings exceed 0.3 ohms repair Ground circuit.
Step 6 Measure Resistance of coil if it is below 0.4 or above 2 ohms replace coil.
Step 7 Measure for continuity between pick up coil chassis harness plug on the Purple , Orange and Black wires and the Ignition module plug.If readings exceed 0.3 ohms on any wire repair harness.
Step 8 Measure for continuity between coil green wire (tach) and Ignition module plug.If readings exceed 0.3 ohms repair harness/wire.
If all the above checks out Ignition module is at fault
Testing sequence. for a totoally unknown no spark fault.
Step 1. Remove Dist cap Crank engine ensure Rotor is turning.
Step 2. Put igntion switch to run. Check for Batt voltage at red wire at Ignition module reduced voltage 6-8V at (batt) red wire on coil. If no voltage is seen at either location repair circuit (wiring, ignition switch ballast resistor)
Step 3 Remove Starter feed from fender Starter relay (optonal) This just keeps you from cranking the engine over while testing and removes the possibility of getting stuff hung up in the fan. If you leave the starter feed hooked up. Put ignition switch to start Check for batt voltage on the white wire at ignition module and the (batt) red wire on coil. If no voltage is seen at either location repair circuit (wiring ignition switch or start relay)
Step 4 Unplug the pick up coil at the dist measure resistance with the Ignition switch off Measure resistance between orange and purple wire on the coil side if the resistance is more than 850 ohms or less than 790 ohms pick up coil is failed replace pick up coil.
Step 5 Measure continuity to ground on the black wire on the dist side of above connector. If readings exceed 0.3 ohms repair Ground circuit.
Step 6 Measure Resistance of coil if it is below 0.4 or above 2 ohms replace coil.
Step 7 Measure for continuity between pick up coil chassis harness plug on the Purple , Orange and Black wires and the Ignition module plug.If readings exceed 0.3 ohms on any wire repair harness.
Step 8 Measure for continuity between coil green wire (tach) and Ignition module plug.If readings exceed 0.3 ohms repair harness/wire.
If all the above checks out Ignition module is at fault
#15
Thanks for the information! Yes, friend and I checked all fuses and fusable link. BUT, another idea was the ballast resistor!! I never knew this truck had one. All symptoms say it may be that. So I found an original on e-Bay and am waiting for it now. Are you familiar with the ballast resistor? I will keep you and everyone posted on results.
Thanks again,
Hunter52
Burbank,CA
Thanks again,
Hunter52
Burbank,CA