351m won't start
Lead Driver
Joined: Jul 2017
Posts: 9,600
Likes: 1,174
From: San Jose, CA
Also, when you tested for compression with your finger, did we ever ask you whether you did that on the front cylinder, passenger side? Can't remember if you're a Ford-only kind of person, or have worked on GM products too, where the cylinders are numbered differently. Or Chrysler, which I am not that familiar with.
Paul
Paul
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Also, when you tested for compression with your finger, did we ever ask you whether you did that on the front cylinder, passenger side? Can't remember if you're a Ford-only kind of person, or have worked on GM products too, where the cylinders are numbered differently. Or Chrysler, which I am not that familiar with.
Paul
Paul
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You can even see full battery voltage to the coil for a short time under some circumstances, or as low as 6v sometimes. A reading of 8 or 9 volts however is pretty healthy.
When you were testing the voltage, how long had the key been on, and was the engine running or not? Check the voltage again when everything is cold, then have someone crank the starter while you're watching the readings. If that 7v is the most you see and it's all down from there, then yes that's too low.
So a little more testing and we should know something more.
For the ICM/ignition control module/brain box/black box, if this is still a Dura Spark setup you need to separate the 2-wire plug with the Red and the White wires, then take a reading on the wire feeding the Red wire and that should be 12v or near battery voltage. The wire feeding the White wire should have voltage only in START.
I don't have the diagram in front of me, but on the body side of the harness I believe the wire colors are Red w/green for the Red wire, and Red w/blue for the White wire. Both I believe come straight from the key on yours. But since you wired it in yourself, you'll have to find the wires you used and test them whatever color they are.
Have we seen any pics of under the hood so we know exactly what you're dealing with? I know you've said, but let's see this puppy!
And when checking voltages it's good to know each time you're working on it just exactly what the battery voltage is at that time. This way you know it when you see a voltage drop. Might be that 11.4v on some random wire is ok when the battery is low, but if you see that reading when the battery has
13v then that 11v means there is a 2v drop on that circuit and, other than the resistor wire, this is never good.
You installed the Dura Spark yourself you said, but where did you get power? Ground? Is the distributor new or used? Was the distributor bore in the block clean, or oily and rusty? If not perfect, electronic ignitions are even more sensitive to bad grounds than points are.
Paul
I don't even have the key wired up yet haha I'm just jumping the engine with a switch between the "S" and the positive battery lug on the starter solenoid
I had it cranking for a bit and I was really only getting 7 volts and nothing changed it stayed 7 volts for the whole time I cranked it. So I wonder if that's my problem?
I tested the ICM like you said the the voltage was the same/ close to the same as the battery and the test light did flicker on the negative lug of the coil so hopefully thats one of the parts that's working right!
shes a little dirty and got crazy wiring at the moment but once she starts up it's gonna look a lot better!
Distributor is new but the bore is a little oily I can try to clean that up maybe that will help
Fleet Mechanic
Joined: Jul 2017
Posts: 1,276
Likes: 12
From: KY
several have converted to an hei module instead of the dura spark , although I have not done it with my f100 , I did do this with a 72 challenger with great success and its still working today after a failed ignition box of china crap , after the 3rd box I used the gm module and runs great now, just a thought if your sure of bad spark
https://www.ford-trucks.com/forums/1...stributor.html
https://www.ford-trucks.com/forums/1...stributor.html
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While 7v is lower than you might think, it's right in the money (well, the low end of the money) range.
But being at the low end might indicate something if we keep looking. The coil uses a resistor wire as we've discussed I think and the whole point of that is to take the battery voltage at the time and reduce it by whatever the rating is.
Ford used slightly different resistance ratings over the years, and resistor wires work on heat (heat is resistance and resistance is heat) so will very. Which is why you NEVER expect an exact voltage reading that the next guy has, and why it can even vary each time. It will always be a "range" of acceptable voltages, so don't expect an exact answer. EVER...
You can even see full battery voltage to the coil for a short time under some circumstances, or as low as 6v sometimes. A reading of 8 or 9 volts however is pretty healthy.
When you were testing the voltage, how long had the key been on, and was the engine running or not? Check the voltage again when everything is cold, then have someone crank the starter while you're watching the readings. If that 7v is the most you see and it's all down from there, then yes that's too low.
So a little more testing and we should know something more.
For the ICM/ignition control module/brain box/black box, if this is still a Dura Spark setup you need to separate the 2-wire plug with the Red and the White wires, then take a reading on the wire feeding the Red wire and that should be 12v or near battery voltage. The wire feeding the White wire should have voltage only in START.
I don't have the diagram in front of me, but on the body side of the harness I believe the wire colors are Red w/green for the Red wire, and Red w/blue for the White wire. Both I believe come straight from the key on yours. But since you wired it in yourself, you'll have to find the wires you used and test them whatever color they are.
Have we seen any pics of under the hood so we know exactly what you're dealing with? I know you've said, but let's see this puppy!
And when checking voltages it's good to know each time you're working on it just exactly what the battery voltage is at that time. This way you know it when you see a voltage drop. Might be that 11.4v on some random wire is ok when the battery is low, but if you see that reading when the battery has
13v then that 11v means there is a 2v drop on that circuit and, other than the resistor wire, this is never good.
You installed the Dura Spark yourself you said, but where did you get power? Ground? Is the distributor new or used? Was the distributor bore in the block clean, or oily and rusty? If not perfect, electronic ignitions are even more sensitive to bad grounds than points are.
Paul
But being at the low end might indicate something if we keep looking. The coil uses a resistor wire as we've discussed I think and the whole point of that is to take the battery voltage at the time and reduce it by whatever the rating is.
Ford used slightly different resistance ratings over the years, and resistor wires work on heat (heat is resistance and resistance is heat) so will very. Which is why you NEVER expect an exact voltage reading that the next guy has, and why it can even vary each time. It will always be a "range" of acceptable voltages, so don't expect an exact answer. EVER...
You can even see full battery voltage to the coil for a short time under some circumstances, or as low as 6v sometimes. A reading of 8 or 9 volts however is pretty healthy.
When you were testing the voltage, how long had the key been on, and was the engine running or not? Check the voltage again when everything is cold, then have someone crank the starter while you're watching the readings. If that 7v is the most you see and it's all down from there, then yes that's too low.
So a little more testing and we should know something more.
For the ICM/ignition control module/brain box/black box, if this is still a Dura Spark setup you need to separate the 2-wire plug with the Red and the White wires, then take a reading on the wire feeding the Red wire and that should be 12v or near battery voltage. The wire feeding the White wire should have voltage only in START.
I don't have the diagram in front of me, but on the body side of the harness I believe the wire colors are Red w/green for the Red wire, and Red w/blue for the White wire. Both I believe come straight from the key on yours. But since you wired it in yourself, you'll have to find the wires you used and test them whatever color they are.
Have we seen any pics of under the hood so we know exactly what you're dealing with? I know you've said, but let's see this puppy!
And when checking voltages it's good to know each time you're working on it just exactly what the battery voltage is at that time. This way you know it when you see a voltage drop. Might be that 11.4v on some random wire is ok when the battery is low, but if you see that reading when the battery has
13v then that 11v means there is a 2v drop on that circuit and, other than the resistor wire, this is never good.
You installed the Dura Spark yourself you said, but where did you get power? Ground? Is the distributor new or used? Was the distributor bore in the block clean, or oily and rusty? If not perfect, electronic ignitions are even more sensitive to bad grounds than points are.
Paul
several have converted to an hei module instead of the dura spark , although I have not done it with my f100 , I did do this with a 72 challenger with great success and its still working today after a failed ignition box of china crap , after the 3rd box I used the gm module and runs great now, just a thought if your sure of bad spark
https://www.ford-trucks.com/forums/1...stributor.html
https://www.ford-trucks.com/forums/1...stributor.html
Yeah ive been looking at just using an HEI or getting an MSD ignition and I'm very annoyed at the ds2 so I'm just gonna upgrade to one of those
Thanks for the replies man your help has been awesome
Lead Driver
Joined: Jul 2017
Posts: 9,600
Likes: 1,174
From: San Jose, CA
Cleaning the bore is not a bad idea, but at least part of the grounding of the distributor is achieved through the clamp. Since yours is not just loose, but the clamp and bolt are not even there, perhaps you can improve things by just locking it down temporarily.
I understand not locking it down while you're messing with it (one more thing to hassle with while making adjustments, but with not much else on the engine, at least you don't have to fight stuff to get to the bolt.
Check under the distributor cap to make sure that the manufacturer installed the grounding screw. You'll see it right where the wires enter the distributor as a metal tab attached to the rubber grommet. Has two holes like wings, but only one is attached to the distributor body.
If neither hole has a screw, put one in. Little shorty thing most likely.
Where is the module and how is it wired? You're not using the key, so are you tapping into wiring somewhere else? Or right to the battery?
And speaking of partial wiring, how many grounds are connected? Did you replace the one between the back of the engine and the firewall? Did you replace the one on the negative battery cable that goes to the body? If not, then your radiator support is the last place you want to use for spark testing.
Use the engine instead, but replace all the grounds that are at least the minimum.
Paul
I understand not locking it down while you're messing with it (one more thing to hassle with while making adjustments, but with not much else on the engine, at least you don't have to fight stuff to get to the bolt.
Check under the distributor cap to make sure that the manufacturer installed the grounding screw. You'll see it right where the wires enter the distributor as a metal tab attached to the rubber grommet. Has two holes like wings, but only one is attached to the distributor body.
If neither hole has a screw, put one in. Little shorty thing most likely.
Where is the module and how is it wired? You're not using the key, so are you tapping into wiring somewhere else? Or right to the battery?
And speaking of partial wiring, how many grounds are connected? Did you replace the one between the back of the engine and the firewall? Did you replace the one on the negative battery cable that goes to the body? If not, then your radiator support is the last place you want to use for spark testing.
Use the engine instead, but replace all the grounds that are at least the minimum.
Paul
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Junior User
Joined: Aug 2019
Posts: 67
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Cleaning the bore is not a bad idea, but at least part of the grounding of the distributor is achieved through the clamp. Since yours is not just loose, but the clamp and bolt are not even there, perhaps you can improve things by just locking it down temporarily.
I understand not locking it down while you're messing with it (one more thing to hassle with while making adjustments, but with not much else on the engine, at least you don't have to fight stuff to get to the bolt.
Check under the distributor cap to make sure that the manufacturer installed the grounding screw. You'll see it right where the wires enter the distributor as a metal tab attached to the rubber grommet. Has two holes like wings, but only one is attached to the distributor body.
If neither hole has a screw, put one in. Little shorty thing most likely.
Where is the module and how is it wired? You're not using the key, so are you tapping into wiring somewhere else? Or right to the battery?
And speaking of partial wiring, how many grounds are connected? Did you replace the one between the back of the engine and the firewall? Did you replace the one on the negative battery cable that goes to the body? If not, then your radiator support is the last place you want to use for spark testing.
Use the engine instead, but replace all the grounds that are at least the minimum.
Paul
I understand not locking it down while you're messing with it (one more thing to hassle with while making adjustments, but with not much else on the engine, at least you don't have to fight stuff to get to the bolt.
Check under the distributor cap to make sure that the manufacturer installed the grounding screw. You'll see it right where the wires enter the distributor as a metal tab attached to the rubber grommet. Has two holes like wings, but only one is attached to the distributor body.
If neither hole has a screw, put one in. Little shorty thing most likely.
Where is the module and how is it wired? You're not using the key, so are you tapping into wiring somewhere else? Or right to the battery?
And speaking of partial wiring, how many grounds are connected? Did you replace the one between the back of the engine and the firewall? Did you replace the one on the negative battery cable that goes to the body? If not, then your radiator support is the last place you want to use for spark testing.
Use the engine instead, but replace all the grounds that are at least the minimum.
Paul
The module is sitting on the passenger side fender until I get it running in which case I will relocate it to the driver side inner fender. Right now I am just hotwiring the starter solenoid to get it to crank
I did ground the firewall to the back of the engine and the negative battery terminal is grounded to the block with a good clean ground. I think ive heard people say they ground spark plugs on the radiator support but I can try the block.
I'll definitely check for a grounding screw and go over the grounds once I get off work tomorrow
Lead Driver
Joined: Jul 2017
Posts: 9,600
Likes: 1,174
From: San Jose, CA
Sounds good. The ground in the distributor is important as it's also the ground for the ignition module. Especially when it's not bolted down to anything.
On the older trucks, Ford's body ground method was a metal clamp at some point along the main negative cable, between the battery and the engine. Somewhere on a metal part of the body the clamp was attached. This not only held the ground cable in place, but also grounded the body.
I think most of us that replace the battery cables will use the type with the added 10ga pigtail, or just run our own 10ga wire from the battery to an existing body bolt either on the top of the fender (where the battery brace is) or on the fender apron where the starter relay bolts down.
If the truck is older (by now they're ALL older!) or spent much of it's time in a rust prone area, the connection between the fenders and the radiator core support is often not as good as it used to be when new. This means dimmer headlights and turn signals, softer horns maybe, and other maladies.
I've had to jumper a separate wire between the fender and the core support on several older vehicles now, to get the lights working better. Not sure if it also helps reduce galvanic reaction in radiators, but it might.
Paul
On the older trucks, Ford's body ground method was a metal clamp at some point along the main negative cable, between the battery and the engine. Somewhere on a metal part of the body the clamp was attached. This not only held the ground cable in place, but also grounded the body.
I think most of us that replace the battery cables will use the type with the added 10ga pigtail, or just run our own 10ga wire from the battery to an existing body bolt either on the top of the fender (where the battery brace is) or on the fender apron where the starter relay bolts down.
If the truck is older (by now they're ALL older!) or spent much of it's time in a rust prone area, the connection between the fenders and the radiator core support is often not as good as it used to be when new. This means dimmer headlights and turn signals, softer horns maybe, and other maladies.
I've had to jumper a separate wire between the fender and the core support on several older vehicles now, to get the lights working better. Not sure if it also helps reduce galvanic reaction in radiators, but it might.
Paul
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Sounds good. The ground in the distributor is important as it's also the ground for the ignition module. Especially when it's not bolted down to anything.
On the older trucks, Ford's body ground method was a metal clamp at some point along the main negative cable, between the battery and the engine. Somewhere on a metal part of the body the clamp was attached. This not only held the ground cable in place, but also grounded the body.
I think most of us that replace the battery cables will use the type with the added 10ga pigtail, or just run our own 10ga wire from the battery to an existing body bolt either on the top of the fender (where the battery brace is) or on the fender apron where the starter relay bolts down.
If the truck is older (by now they're ALL older!) or spent much of it's time in a rust prone area, the connection between the fenders and the radiator core support is often not as good as it used to be when new. This means dimmer headlights and turn signals, softer horns maybe, and other maladies.
I've had to jumper a separate wire between the fender and the core support on several older vehicles now, to get the lights working better. Not sure if it also helps reduce galvanic reaction in radiators, but it might.
Paul
On the older trucks, Ford's body ground method was a metal clamp at some point along the main negative cable, between the battery and the engine. Somewhere on a metal part of the body the clamp was attached. This not only held the ground cable in place, but also grounded the body.
I think most of us that replace the battery cables will use the type with the added 10ga pigtail, or just run our own 10ga wire from the battery to an existing body bolt either on the top of the fender (where the battery brace is) or on the fender apron where the starter relay bolts down.
If the truck is older (by now they're ALL older!) or spent much of it's time in a rust prone area, the connection between the fenders and the radiator core support is often not as good as it used to be when new. This means dimmer headlights and turn signals, softer horns maybe, and other maladies.
I've had to jumper a separate wire between the fender and the core support on several older vehicles now, to get the lights working better. Not sure if it also helps reduce galvanic reaction in radiators, but it might.
Paul
I installed the new ignition and finished wiring the whole harness and added a few grounds from the block to the firewall and the block to the frame. now when I measure positive lug of the battery it tells me 12v when in "run" on the ignition switch and 10v while it's cranking. Is 10v enough for an engine to start? Is 12v too much in run? Distributor bore is clean as a whistle. Would my aluminum intake manifold be the reason for this? From what I've read the coil is grounded to the intake through the bracket
Lead Driver
Joined: Jul 2017
Posts: 9,600
Likes: 1,174
From: San Jose, CA
No, aluminum is fine in this situation. Even the factories use aluminum intakes and even whole engines.
No such thing as 12v being too much under any circumstances for cranking. The only place you normally want to see less is the Red w/green resistor wire and the White w/black stator wire to the electric choke. Everything else totally wants to see 12v.
The 10v while cranking is officially too low, but it might be just the way the gauge reads during that huge surge/drain. If the starter is spinning the engine over at the normal fast rate, there is still enough voltage to fire the plugs and start the engine.
Did you make sure to re-connect the Brown wire on the "I" post of the starter relay, so that the ignition coil gets it's extra share of power while starting?
Did you re-verify that you have spark while cranking?
Did you re-verify that you have plenty of fuel? Even though not even coughing on starting fluid is a good indication that fuel is not the issue.
Did you put a timing light on the number one plug wire and check timing while cranking? You could still be way off in your timing.
Paul
No such thing as 12v being too much under any circumstances for cranking. The only place you normally want to see less is the Red w/green resistor wire and the White w/black stator wire to the electric choke. Everything else totally wants to see 12v.
The 10v while cranking is officially too low, but it might be just the way the gauge reads during that huge surge/drain. If the starter is spinning the engine over at the normal fast rate, there is still enough voltage to fire the plugs and start the engine.
Did you make sure to re-connect the Brown wire on the "I" post of the starter relay, so that the ignition coil gets it's extra share of power while starting?
Did you re-verify that you have spark while cranking?
Did you re-verify that you have plenty of fuel? Even though not even coughing on starting fluid is a good indication that fuel is not the issue.
Did you put a timing light on the number one plug wire and check timing while cranking? You could still be way off in your timing.
Paul
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No, aluminum is fine in this situation. Even the factories use aluminum intakes and even whole engines.
No such thing as 12v being too much under any circumstances for cranking. The only place you normally want to see less is the Red w/green resistor wire and the White w/black stator wire to the electric choke. Everything else totally wants to see 12v.
The 10v while cranking is officially too low, but it might be just the way the gauge reads during that huge surge/drain. If the starter is spinning the engine over at the normal fast rate, there is still enough voltage to fire the plugs and start the engine.
Did you make sure to re-connect the Brown wire on the "I" post of the starter relay, so that the ignition coil gets it's extra share of power while starting?
Did you re-verify that you have spark while cranking?
Did you re-verify that you have plenty of fuel? Even though not even coughing on starting fluid is a good indication that fuel is not the issue.
Did you put a timing light on the number one plug wire and check timing while cranking? You could still be way off in your timing.
Paul
No such thing as 12v being too much under any circumstances for cranking. The only place you normally want to see less is the Red w/green resistor wire and the White w/black stator wire to the electric choke. Everything else totally wants to see 12v.
The 10v while cranking is officially too low, but it might be just the way the gauge reads during that huge surge/drain. If the starter is spinning the engine over at the normal fast rate, there is still enough voltage to fire the plugs and start the engine.
Did you make sure to re-connect the Brown wire on the "I" post of the starter relay, so that the ignition coil gets it's extra share of power while starting?
Did you re-verify that you have spark while cranking?
Did you re-verify that you have plenty of fuel? Even though not even coughing on starting fluid is a good indication that fuel is not the issue.
Did you put a timing light on the number one plug wire and check timing while cranking? You could still be way off in your timing.
Paul
Now that I think of it my starter might be on the slow side. It does get 12v but it's also not as fast as my 2007 truck but I figured that was because it was a larger/older engine. I'll look up videos of 351M's cranking and I'll see how much slower mine is
Yessir I made sure that there was a wire from the I to the coil positive. I did also check for spark and it is still orange which is why I've been sitting here scratching my head for a while nothing really seems to change the spark color. I've got alot of fuel and have used a little bit of starting fluid but have been staying away from using alot of it.
I haven't used a timing light on it yet that's next on the list for when all of the coronavirus stuff dies down. I have triple checked tdc on front cylinder passenger side and made sure it lines up with the distributor #1 spark plug
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👍 Thank you
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Whenever I crank the engine I just get puffs of exhaust through the headers and sometimes a loud backfire through the headers if that helps explain anything to you
I've flipped around the distributor every which way and swapped the wires 270 degrees like someone mentioned on this thread but all that did was make air pop out of the carb
I've flipped around the distributor every which way and swapped the wires 270 degrees like someone mentioned on this thread but all that did was make air pop out of the carb
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