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Engine won’t shut off
#1
Hey guys I’m having electrical problems with my 72 Mach1 with a recently rebuilt 351 Cleveland. I have tried to look the up with the search but I can’t figure out what is going on. My car is very clean and restored. It has an electronic VR, which isn’t very old and I have the pertronix I for the ignition.
So when I turn the key to the off position it continues to run like normal, not dieseling. It doesn’t do it all the time, but is becoming more frequent. I can tell when it’s not going to shut down cause my factory tach quits working. I did find a bad connection at the I terminal of the starter relay, but I fixed that and I got the same thing. 
I removed the wire from the I terminal of the relay while it was still running, thought it would shut down but it didn’t. So then I looked at my tach and it was working again and I turned the key to the off position and it shut down.
I can start the car with the I terminal disconnected and it will keep running. I checked the voltage and I get 5.3 at the coil positive with engine off in the run position and 3.8 when engine is running. Now that’s with me touching the ground to the coil ground. 
Sorry if I’m not trying or testing the correct stuff but I’m pretty confused about what is wrong. 
Now I just connected the I terminal back up and started the engine. Tach is working and I shut it off and back on a few times. I have some kind of intermittent connection happening. So anyway I sure could use some help! Thanks.[Image: D4-B88-AE8-A1-EA-4162-9834-488-C4773-B48-F.jpg]

run_horse Run Horse Run!
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#2
The next time it won't shut off leave the key in the off position and then remove the red with light green stripe wire from the "I" terminal on the solenoid. This is the 3rd or 4th bad solenoid in the last couple of weeks. By any chance did you get it from Scott Drake?

You will get different voltage readings with the engine running and with the coil grounded. When the engine is running the voltage fluctuates from high to low as the coil discharges and energizes. It acts more like a digital signal, and the only way to read the high and low voltages is with more sophisticated test instruments like an oscilloscope.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#3
Don, I did have the key in the off position and it kept running. I then turned it to the run position and then back to off and it stopped running. I can start the car and then it will keep running with the wire removed from the I terminal.

run_horse Run Horse Run!
John 72 Q Code
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#4
When the key is in the run position the engine should keep running with the wire removed from the "I" terminal. The only time the "I" terminal wire has full battery voltage is when the engine is being cranked and is energized at the same time the starter is energized. There are two sets of contacts in the solenoid, one to provide connection and battery voltage to the starter, the other to provide full battery voltage to the coil when starting. It sounds like the "I" terminal contact sticks intermittently. This has become a fairly common problem with some solenoids. The only reliable ones seem to be from Ford and from NAPA.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#5
(08-11-2019, 08:36 PM)Don C Wrote: When the key is in the run position the engine should keep running with the wire removed from the "I" terminal. The only time the "I" terminal wire has full battery voltage is when the engine is being cranked and is energized at the same time the starter is energized. There are two sets of contacts in the solenoid, one to provide connection and battery voltage to the starter, the other to provide full battery voltage to the coil when starting. It sounds like the "I" terminal contact sticks intermittently. This has become a fairly common problem with some solenoids. The only reliable ones seem to be from Ford and from NAPA.
Oh ok, thanks Don. I have a Ford solenoid relay on the way. I do know that the shop that rebuilt my car said he does have really good luck with whatever solenoid they got. Pretty sure they do use NAPA parts, but not positive.
So will a bad solenoid make my tach not work?

run_horse Run Horse Run!
John 72 Q Code
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#6
Yes, when the "I" contact is stuck, in the solenoid, the coil will be primarily powered from the solenoid instead of the ignition switch. Electricity is like water, it flows through the easiest channel, so the resistor wire restricts the flow from the ignition switch and through the tachometer, and the coil runs on the battery voltage from the solenoid, bypassing the tachometer.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#7
(08-11-2019, 08:56 PM)Don C Wrote: Yes, when the "I" contact is stuck, in the solenoid, the coil will be primarily powered from the solenoid instead of the ignition switch. Electricity is like water, it flows through the easiest channel, so the resistor wire restricts the flow from the ignition switch and through the tachometer, and the coil runs on the battery voltage from the solenoid, bypassing the tachometer.
Gotcha. Thanks again Don! When I get the new solenoid I will post results. Hopefully that does it. I live in Michigan and the dream cruise and the Mustang Memories show are next weekend and I sure would like to have this all figured out.

run_horse Run Horse Run!
John 72 Q Code
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#8
I just ordered a Motorcraft #sw-7663 starter solenoid from orileys for 26 bucks. They will have it ready for me to pick up in a few hours. So hopefully it’s good and I can be done with my ignition problems. Anyway, I am getting a better grasp on how it works.

run_horse Run Horse Run!
John 72 Q Code
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#9
Let us know how it works out, also if you can verify where the one you have now came from. If it's from NAPA I'll add them to my don't buy list.

I would use a Motorcraft solenoid or voltage regulator from a salvage yard before I would buy a new one from most places. My electronic voltage regulator came from Pic-N-Pull 15 years ago and the last time I had it running (been over a year) it still worked fine.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#10
(08-12-2019, 08:56 AM)Don C Wrote: Let us know how it works out, also if you can verify where the one you have now came from. If it's from NAPA I'll add them to my don't buy list.

I would use a Motorcraft solenoid or voltage regulator from a salvage yard before I would buy a new one from most places. My electronic voltage regulator came from Pic-N-Pull 15 years ago and the last time I had it running (been over a year) it still worked fine.

Same here. A new BWD unit from Advance took out my MSD 6AL about ten years ago. Pulled a nasty, crusty Motorcraft unit out of one of my parts boxes and it's been working perfectly ever since. Just cleaned it up a little and swapped the tall blue early style cover over onto it. 

I've been running a used Motorcraft D2 starter solenoid since I finished the engine compartment in 2003. When I put the new 351C in next year, it's going to have a PMGR Ford starter with integral solenoid, so that M'craft D2 solenoid will probably outlast me.


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