70' 351C Starts But Will Not Stay Running?

[Fotoman]

Hello All,

I have a 1970 Mach 1 with a 351C. I installed a complete MSD ignition system, Distributor, Digital 6A Box, & Coil. The Motor ran Awesome & was a Blast to drive. However, the MSD distributor was to tall to install my Shaker Hood Scoop back
on the motor. So, I had to install a Mallory distributor that was short enough to
work with the Shaker Hood Scoop. I really wish that the fine people at MSD would
have warned me about this problem? Anyway, MSD said that the Mallory distributor would work just fine with there 6A Box & Coil. Well, it dosen't. The Motor will start
just fine, however it will Not stay running? Going by there specs all the wires are hooked up correctly. Dose anybody have any ideas what the problem may be? I'd
really like to go for a ride and show this baby off.

 

[69gmachine]

Does it run only while the key is in the START position and then die when it is returned to the ON (RUN) position? If yes, then you are only getting 12 volts to the coil from the starter solenoid and not from the ignition switch.

 

[Fotoman]

Does it run only while the key is in the START position and then die when it is returned to the ON (RUN) position? If yes, then you are only getting 12 volts to the coil from the starter solenoid and not from the ignition switch.

YES! that is the issue 69machine, thaks for your reply. So, why would that change from just exchanging the distributor? She ran Awesome with the MSD distributor installed, and all I did was install the smaller Mallory
distributor that would work with my Shaker hood? Any ideas of what I could try to solve this problem? I'd
really like to take it out for a ride and do some Burnouts.

 

[69gmachine]

You need to get a voltmeter to figure out where you're not getting power. If you take a reading at the coil while the key is ON but not START, you will find you have no power, so you need to work backwards to find out where it got lost. Something is disconnected in the ignition circuit ahead of the coil.

 

[Fotoman]

You need to get a voltmeter to figure out where you're not getting power. If you take a reading at the coil while the key is ON but not START, you will find you have no power, so you need to work backwards to find out where it got lost. Something is disconnected in the ignition circuit ahead of the coil.

Thank you again for your reply 69gmachine. I'll try this tonight.

 

[Fotoman]

You need to get a voltmeter to figure out where you're not getting power. If you take a reading at the coil while the key is ON but not START, you will find you have no power, so you need to work backwards to find out where it got lost. Something is disconnected in the ignition circuit ahead of the coil.

OK, I checked out all the wiring and here is what I found. With the key @ the On position, I'm getting 12 volts to my MSD Digital 6A box and the red indicator light is on. The Red wire (ignition) from the MSD box is getting 12 Volts from my ignition switch. However, there is Nothing @ the + side of the coil??? How is this possible? There is 12 Volts everywhere there is supposed to be except the Coil? WTF! There is 12 Volts going to the MSD 6A, but Nothing coming out? Dose anybody have any ideas?

 

[Fotoman]

I also performed a spark test on the MSD and it passed. So, I'm getting Spark with the key
in the start position, however Not in the On position. Oh by the way I'm using a Mallory
distributor with a Magnetic pickup. Any Ideas anybody??? HELP!

 

[BarnStang]

Page 23 of the MSD 6a instructions shows the wiring diagram for a mallory dist with mag pickup. If you are wired correctly and you have no 12v on the orange wire at the coil + then its possible your MSD box may have failed.
http://www.msdignition.com/uploadedFiles/MSDIgnitioncom/Products/Ignitions/6420_instructions.pdf
Also, how are you supplying 12v to the red wire on the MSD box? If you spliced to the old coil wire you are running power from the ign switch through the resistor wire (ballest). You may want to check that too. From page 5 of the same instructions:
Ballast Resistor:
If your vehicle has a ballast resistor in line with the coil wiring, it is recommended to bypass it.

 

[Fotoman]

Page 23 of the MSD 6a instructions shows the wiring diagram for a mallory dist with mag pickup. If you are wired correctly and you have no 12v on the orange wire at the coil + then its possible your MSD box may have failed.
http://www.msdignition.com/uploadedFiles/MSDIgnitioncom/Products/Ignitions/6420_instructions.pdf
Also, how are you supplying 12v to the red wire on the MSD box? If you spliced to the old coil wire you are running power from the ign switch through the resistor wire (ballest). You may want to check that too. From page 5 of the same instructions:
Ballast Resistor:
If your vehicle has a ballast resistor in line with the coil wiring, it is recommended to bypass it.

Thanks for your reply BarnStang. Yes, the wiring is correct per the MSD instructions for a Mag pickup. the 12 Volts is coming directly from the ignition switch like it always has, and there is No ballest resistor. Funny thing is that it passed the MSD Mag pickup Spark test? So, it's getting power @ start. There is 12 Volts @ the MSD Red Wire. Everything worked perfect with the MSD # 8350 RTR distributor installed, all I did was replace the MSD with a Mag pick up Mallory distributor? so I could install my Shaker hood. Any other ideas? Or should I try replacing the MSD Digital 6A Box?

 

[BarnStang]

"12 Volts is coming directly from the ignition switch like it always has, and there is No ballest resistor"

Still not quite clear. The instructions show 12v from the switch-how EXACTLY are you getting 12v from the switch?

THe instructions show an Orange wire from the MSD box to the coil + but you say "like it always has" If you have the original factory harness coil + wire connected to the new coil + post, then you have the resistor wire in series between the ign switch and the coil +. It is built into the harness-it is not a cermic block like a mopar. Inside the harness under the dash it is a long pink wire. THe insulation will feel differently to the touch compared to all the other wires in the harness...you would need to cut the harness open to see it.
You can source the 12v from the switch, but you need to be right at the switch BEFORE the harness starts the pink wire...that will get you 12v to the MSD red wire with no resistance.

 

[Fotoman]

"12 Volts is coming directly from the ignition switch like it always has, and there is No ballest resistor"

Still not quite clear. The instructions show 12v from the switch-how EXACTLY are you getting 12v from the switch?

THe instructions show an Orange wire from the MSD box to the coil + but you say "like it always has" If you have the original factory harness coil + wire connected to the new coil + post, then you have the resistor wire in series between the ign switch and the coil +. It is built into the harness-it is not a cermic block like a mopar. Inside the harness under the dash it is a long pink wire. THe insulation will feel differently to the touch compared to all the other wires in the harness...you would need to cut the harness open to see it.
You can source the 12v from the switch, but you need to be right at the switch BEFORE the harness starts the pink wire...that will get you 12v to the MSD red wire with no resistance.

OK, I'm sorry I guess I'm missing something? Like I said the Engine was running Great with the
Model 8350 RTR MSD Distributor installed. All I did was replace the MSD with a shorter Mallory
Mag pickup distributor and connect the proper wires per the MSD instructions. All I know is, there
is power going to the Red wire on the MSD 6A box with the key in the on position, the Red light on
the 6A is on, and I have No Voltage at the Orange wire (Coil +) I performed a Spark test per the
MSD instructions and I have spark at the Coil Wire. So, I guess I'm just totally lost? Maybe it's
time to just get it towed to a shop and spend some $$$ to have them figure it out.

 

[BarnStang]

In the Start position, the factory ign system gets full 12v from the solinoid "I" terminal. In Run, it comes through the resistor wire. Regardless of the red light on the MSD box, WHERE is the 12v coming from that is feeding the MSD box???

Looking over the MSD dist inst, what did you do with the white wire from the MSD box?? With the Mallory, it should not be connected to anything, in fact, it can be used to disable the ign system...

It sounds like you have everything else connected correctly. And you may not see 12v at the coil + post...

Is this the spark test you are conducting?

If triggering with the Magnetic Pickup:
1. Make sure the ignition switch is in the "Off" position.
2. Remove the coil wire from the distributor cap and set the terminal approximately 1/2" from ground.
3. Disconnect the MSD magnetic pickup wires from the distributor.
4. Turn the ignition to the On position. Do not crank the engine.
5. With a small jumper wire, short the MSD's Green and Violet magnetic pickup wires together. Each time you break this short, a spark should jump from the coil wire to ground. If spark is present, the ignition is working properly. If there is no spark skip to step 6 below:
6.

If there is no spark:
A. Inspect all of the wiring.

B. Substitute another coil and repeat the test. If there is now spark, the coil is at fault.

C. If there is still no spark, check to make sure there is 12 volts on the small Red wire from the MSD when the key is in the On position. If 12 volts is not present, find another switched 12 volt source and repeat the test.

D. If, after following the test procedures and inspecting all of the wiring, there is still no spark, the MSD Ignition is in need of repair. See the Warranty and Service section for information.
The following wiring diagrams illustrate numerous installations on different vehicles and applications. If you experience difficulties when installing your MSD, contact our Customer Support Department at (915) 855-7123 (7 - 6 Mountain time) or e-mail us at:
[email protected]

You may want to call tech supportto confirm if there is a problem with the MSD box if you are getting a good spark test with the switch in the Run position.

 

[Fotoman]

In the Start position, the factory ign system gets full 12v from the solinoid "I" terminal. In Run, it comes through the resistor wire. Regardless of the red light on the MSD box, WHERE is the 12v coming from that is feeding the MSD box???

Looking over the MSD dist inst, what did you do with the white wire from the MSD box?? With the Mallory, it should not be connected to anything, in fact, it can be used to disable the ign system...

It sounds like you have everything else connected correctly. And you may not see 12v at the coil + post...

Is this the spark test you are conducting?

If triggering with the Magnetic Pickup:
1. Make sure the ignition switch is in the "Off" position.
2. Remove the coil wire from the distributor cap and set the terminal approximately 1/2" from ground.
3. Disconnect the MSD magnetic pickup wires from the distributor.
4. Turn the ignition to the On position. Do not crank the engine.
5. With a small jumper wire, short the MSD's Green and Violet magnetic pickup wires together. Each time you break this short, a spark should jump from the coil wire to ground. If spark is present, the ignition is working properly. If there is no spark skip to step 6 below:
6.

If there is no spark:
A. Inspect all of the wiring.

B. Substitute another coil and repeat the test. If there is now spark, the coil is at fault.

C. If there is still no spark, check to make sure there is 12 volts on the small Red wire from the MSD when the key is in the On position. If 12 volts is not present, find another switched 12 volt source and repeat the test.

D. If, after following the test procedures and inspecting all of the wiring, there is still no spark, the MSD Ignition is in need of repair. See the Warranty and Service section for information.
The following wiring diagrams illustrate numerous installations on different vehicles and applications. If you experience difficulties when installing your MSD, contact our Customer Support Department at (915) 855-7123 (7 - 6 Mountain time) or e-mail us at:
[email protected]

You may want to call tech supportto confirm if there is a problem with the MSD box if you are getting a good spark test with the switch in the Run position.

Thank you again for your reply BarnStang. I have the wire that is connected to the MSD box (small red wire) spliced into my ignition switch wire and it has power when
checked with a 12 Volt test light. The White wire from the MSD box is taped off and Not used. YES! that is the same spark test that I performed and I had Spark. I just don't think the MSD Box & Coil like the Mallory distributor? I did call the MSD Tech line and they were not to much help. I think they were a little upset that I was using a Mallory distributor in the first place. I told them that until they made a shorter distributor that would work on a 1970 Mach 1 with a Shaker hood I have No choice. All they said was to try hooking up the distributor directly to the coil and see if the engine starts? So, I guess I'll try that, and if it works the MSD Box is Bad? HA! and I thought this would be easy?

 

[BarnStang]

"I have the wire that is connected to the MSD box (small red wire) spliced into my ignition switch wire and it has power when checked with a 12 Volt test light"

WHERE is the splice physically located???? If you are spliced AFTER the resistance wire (in the engine compartment) , you are not getting full current 12v to the MSD box. If you are spliced into the ign wire physically at the switch under the dash, then your spliced BEFORE the resistance wire and you are good. As I posted before, the MSD instructions recommend NOT running power through the ballest resistance wire...it does not matter that it ran before, the variables have changed. You were not using a mag pickup before, now you are, and the vendor of the dist has changed. It may not make any difference to correct that but it needs to be eliminated as a variable. You can simply run a wire from the battery to the red wire on the MSD to bypass the ign switch. And see if it runs.

Your earlier post said you had a good spark test in START but not in RUN. If you are getting a good spark test in run, it should run.

 

[Fotoman]

"I have the wire that is connected to the MSD box (small red wire) spliced into my ignition switch wire and it has power when checked with a 12 Volt test light"

WHERE is the splice physically located???? If you are spliced AFTER the resistance wire (in the engine compartment) , you are not getting full current 12v to the MSD box. If you are spliced into the ign wire physically at the switch under the dash, then your spliced BEFORE the resistance wire and you are good. As I posted before, the MSD instructions recommend NOT running power through the ballest resistance wire...it does not matter that it ran before, the variables have changed. You were not using a mag pickup before, now you are, and the vendor of the dist has changed. It may not make any difference to correct that but it needs to be eliminated as a variable. You can simply run a wire from the battery to the red wire on the MSD to bypass the ign switch. And see if it runs.

Your earlier post said you had a good spark test in START but not in RUN. If you are getting a good spark test in run, it should run.

Well, I purchased a Actron digital Multimeter so I could test and find out the exact voltage. I must have done something
right, because at the wire coming from my ignition key I have 12.17 volts with the Key in the On position & this wire is
connected to the small Red wire on the MSD box. So. it sould work? And I don't understand why it dosen't? Are there
any other tricks I can try? or do you have any other ideas? I'll be at it again tomorrow. Thank you for your help.

 

[BarnStang]

Can't think of anything else. I will be interested to see what ends up being the problem.

 

[Slobin3d]

wouldn't an easy way to be 100% it's not the ignition be to Hot wire the On 12v to the battery and bypass the key switch all together. if it runs with direct battery voltage it's the key switch/splice. If it still doesn't work its the MSD box. BTW just because it reads 12v doesn't mean it can supply full amperage required

 

[bareje]

Hey Fotoman,
I found this old post from you. I'm having a similar problem with my 351C. Just had my engine rebuilt and added an MSD distributor and I can't get it to stay running. I'm curious what your problem ended up being and how you fixed it. Any advice?

 

[DocUsn]

Hey Fotoman,
I found this old post from you. I'm having a similar problem with my 351C. Just had my engine rebuilt and added an MSD distributor and I can't get it to stay running. I'm curious what your problem ended up being and how you fixed it. Any advice?

Try running your hot wire from the postive side of the solenoid!

 

[DocUsn]

Horse Sence is a very good knowledgeable guy who gave me that advice!