MSD 6 Offroad & Rev Control - Engine Keeps Running

[Jeff10]

Hi Everyone,

I know it's tough to troubleshoot electrical in a forum. That being said, I was hoping maybe someone else has experienced something similar to what is going on with me and the '70.

The motor is a 347 stroker. Ignition is MSD 6 Offroad with Rev Control and an MSD electronic coil.

Although it has been about a year since the motor has been started, there was a consistent problem since the Bronco was worked on at the last shop.

The motor runs fine with that ignition. The problem is when the key is turned off the motor continues to run. It was intermittent at first; but, towards the end it was consistently that way.

I have checked the 12v switched power to the controller. It is on when the key is on, and off when in the off position.

MSD has been gobbled up by Holley. I wrote them over the weekend; but, I haven't heard back from them.

Other than the switched power working correctly, what else might I consider that would keep the motor from shutting off? Hoping someone else may have experienced a similar issue.

Thanks,

Jeff

 

[DirtDonk]

If this is still a stock type wiring harness, pull the small brown wire from the “I” post on the starter relay and see if the problem persists.

 

[Jeff10]

Hi Paul,

Thanks for your input!

I will take a look later today. A new Painless harness was installed shortly before the problem began. Right after installation I was told by the person who did the work that there weren't any issues with the motor shutting off. It was shortly after that when some of the wiring work was cleaned up that the problem began.

I'll keep you posted.

Jeff

 

[DirtDonk]

A starter relay (especially if it's a recent replacement) can fail after awhile. Might have been fine at first but be acting up.
Same for an ignition switch.

Since there was some messing about with the wiring though, it's a tough call from here.
Definitely keep us posted!

Paul

 

[Jeff10]

Hi Paul,

You're up late!

Your comment about the starter relay is a good thing to look at. I don't remember if the relay was replaced with new when most of the work was done. If it is acting up would not shutting the motor off be an indication of that?

The key switch was new when the harness was installed. Although, I know that being new doesn't mean that it can't be bad or fail.

If your suggestion about the brown wire doesn't solve the problem, I will replace the starter relay, just to rule it out.

Thanks!

Jeff

 

[DirtDonk]

Don't replace a working relay. If pulling the Brown wire does not stop the issue, then there is no way it can be a faulty relay.
What can happen when it is the relay, is that somehow power is shorting internally to that small post so instead of having power only when in START, it's got power any time it's in RUN.
It has power on the wire itself anytime the key is On (because it's connected to the coil wire) but if you remove the wire then there should be zero power on the "I" post of the relay.
So you really don't even have to start the engine to test this theory. Simply turn the key ON and remove the wire. Look for voltage at the "I" post and if none, then it's not your issue.
If you do, then replace the relay.

If you have power to the Brown wire when the key is OFF, that is your issue. But finding out where the power is coming from is going to be more work. Could be coming from somewhere along the wire if it's shorted to another wire with constant power, but the more likely culprit is that new ignition switch.
As you said, new doesn't mean it's good. Generally the Painless provide switches are of decent quality, but decent only gets you so far these days. They're all (or almost all) from overseas somewhere and built substandard to what we got used to in the old days.
Definitely not unheard of for a brand new ignition switch to fail within a very short time.

And yes, it's time to turn off the computer!
Was trying to get some important home-loan paperwork done and instead got to reading e-mails and checking the forum. Because I think it is my home!

Later

paul

 

[Jeff10]

Hi Paul,

Great explanation!

Thank you.

I'll report back.

Jeff

 

[DirtDonk]

Since it does "turn off" sometimes, such as after the engine is off and you turn the key back on and it does not start (correct?) then it might be a temporary short of the type that some people "fix" by smacking the relay with something.
I've never had that happen, but over the years have heard many times that someone had to smack their relay when the starter stuck on and was spinning even after the key was released.

Seems more likely to be the ignition switch then, but all bets are still on the table at this point. Plus some we haven't thought of yet!

Paul

 

[Jeff10]

Hi Paul,

The problem isn't the starter is always engaged. The problem is that when the motor is running, and the key switch is turned off, the engine won't stop. The engine does start.

I probably didn't do the best job explaining that.

I'll take a closer look at the Bronco later.

Thanks

Jeff

 

[DirtDonk]

No, I got what you were saying. It was clear. Just listed that second issue as another (the more common) symptom of a failing relay.
Not that yours was continuing to crank, just that when that does happen sometimes smacking the relay releases it and stops the cranking.

Interested to hear what you find. The fact that it started after you were messing with the wires leans towards something along that path. But the fact that some of these components are so prone to failure could mean it's one of those pesky coincidental failures we run afoul of so often here.

Like when you wash and wax your car and the brake light, or turn signal switch stops working. Or spend the whole day putting in new carpet and throw a rod or lunch a transmission the next day!
You know... Fun stuff to deal with.

Paul

 

[Jeff10]

Hi Paul,

There's NO power through the brown wire when the switch is off.

Maybe I should wait until I can try to start it again before I waste everyone's time any further.

Have you ever seen a kill switch installed on a MSD ignition system that can be used rather than stalling the motor by popping the clutch if the motor won't shut off normally?

Thanks again for all of your advice.

Jeff

 

[walls]

Electric fans are known to back feed and cause this issue. When you shut the motor off the electric fan keeps spinning for 10-15 seconds and it acts like an alternator feeding the electrical system and will cause the motor to continue to run until it stops spinning.

 

[1970 Palmer]

Electric fans are known to back feed and cause this issue. When you shut the motor off the electric fan keeps spinning for 10-15 seconds and it acts like an alternator feeding the electrical system and will cause the motor to continue to run until it stops spinning.

Exactly, so do the single wire alternators. The cure is to install a diode (it's just a one way electric valve) in the excite circuit to prevent the feed back after the ignition is switched off. Make sure you install the diode in the correct polarity direction. The electric cooling fans need to be wired through a relay, to prevent the problem.

I got busted on this very subject by an NHRA tech years ago, when she checked my battery shut off switch operation with the engine running.

 

[walls]

Exactly, so do the single wire alternators. The cure is to install a diode (it's just a one way electric valve) in the excite circuit to prevent the feed back after the ignition is switched off. Make sure you install the diode in the correct polarity direction. The electric cooling fans need to be wired through a relay, to prevent the problem.

I got busted on this very subject by an NHRA tech years ago, when she checked my battery shut off switch operation with the engine running.

100% forgot to mention the 1 wire alternator also.

 

[bronconut73]

Electric fans are known to back feed and cause this issue. When you shut the motor off the electric fan keeps spinning for 10-15 seconds and it acts like an alternator feeding the electrical system and will cause the motor to continue to run until it stops spinning.

I chased that issue for a few years in the 90's.

 

[Jeff10]

Hi Guys,

There is no electric fan; however, there is a 1-wire alternator.

Just to clarify, with the alternator are you saying that if the diode isn't installed, the motor will keep running indefinitely (as opposed to the fan issue where it only runs as long as the fan is spinning)?

Thanks,

Jeff

 

[walls]

Hi Guys,

There is no electric fan; however, there is a 1-wire alternator.

Just to clarify, with the alternator are you saying that if the diode isn't installed, the motor will keep running indefinitely (as opposed to the fan issue where it only runs as long as the fan is spinning)?

Thanks,
Yes sir. My one wire alternator did not cause the issue but the fan did. Usually a relay will stop the fan problem but for some reason the way I wired it through the holley sniper fuel injection it still required a diode. I believe a diode on your alternator wire will take care of your problem.

Jeff

Yes sir. My one wire alternator did not cause the issue but the fan did. Usually a relay will stop the fan problem but for some reason the way I wired it through the holley sniper fuel injection it still required a diode. I believe a diode on your alternator wire will take care of your problem.

 

[DirtDonk]

But there's no wire to put it on when using on one wire alternator. Correct? There's no connection that can feed back into the system.
There's no green with red keyed power wire and the yellow sensing wire typically just attaches to the alternator output.
The only other wire attached to the alternator is the large battery cable charge wire.

 

[walls]

But there's no wire to put it on when using on one wire alternator. Correct? There's no connection that can feed back into the system.
There's no green with red keyed power wire and the yellow sensing wire typically just attaches to the alternator output.
The only other wire attached to the alternator is the large battery cable charge wire.

Sorry, worded that wrong, I believe I put it on the coil wire so it stops feeding the ignition. Was probably 20ys ago, the one wire alternator I have on my truck now didnt cause an issue so no diode was needed.