Engine miss caused by overdrive

[Bruce Compton, Canada]

My '49 has developed an occasional miss like the ignition is momentarily shut off and I suspect something in the overdrive wiring, or relay, or kick-down switch, or solenoid. Anyone else experienced this??

[51 MERC-CT]

Perhaps the overdrive relay needs attention.
Don't know the precise way it operates but it actually is supposed to momentarily kill the ignition while up/down shifting.

[Planojc]

Remove the relay fuse and see if the miss is still there.

[pistonbroke]

Simply take the OD wire off your coil. If the miss goes away your kick down switch or your solenoid is compromised. I would lean toward the Kick down switch. Tim

[Bruce Compton, Canada]

Thanks Tim; That's what I plan to do today. I'll let you know what I find. Bruce

[Bruce Compton, Canada]

Sponsored Links (Register now to hide all advertisements)

Well Tim, I took the OD wire off the coil and went for a spin.....and no miss. I reconnected the wire, went for a spin and .....no miss either. I had a new kick-down switch so I installed it as well and everything seems fine.....for now. It's random and usually under load so now I'm suspecting the coil itself.

[Tinker]

Could be coil or condenser. Could be fuel. Fun! Could be valves hanging up under acceleration or load.


Reading the prior comments I wondered how the OD wiring could effect the motor. Like the rear lights, how could that effect the motor... I suppose the rpm gear change could cause the motor to fault if there was an issue with the motor.

[tubman]

"Tinker", please familiarize yourself on how these units function in these cars. Pay particular attention to the electrical part.

[Tinker]

I've had one in a 53. Worked great.


All the electrical elements control the transmission (solenoid). Not the motor.

[tubman]

Originally Posted by Tinker

I've had one in a 53. Worked great.

The vast majority of people have stuff that "worked great" but don't have the slightest understanding of how it works. And then things break when they're old.

Do yourself a favor and take my advice before you embarrass yourself further.

[Tinker]

Okay, thanks! So how does the transmission solenoid electrics effect the motor. School me!

[tubman]

There is a wire from the kickdown switch (under the gas pedal) that goes to the coil and shorts it out to kill the engine for an instant when the kickdown is activated. Any problem with that circuit or that switch can cause this sort of problem.

Since the accelerator has to be floored to activate this switch, the engine would be at full power just as the overdrive is trying to change, which is not a good situation. Got it?

[Tinker]

Originally Posted by tubman

There is a wire from the kickdown switch (under the gas pedal) that goes to the coil and shorts it out to kill the engine for an instant when the kickdown is activated. Any problem with that circuit or that switch can cause this sort of problem.

Since the accelerator has to be floored to activate this switch, the engine would be at full power just as the overdrive is trying to change, which is not a good situation. Got it?

I got it! and a great explanation. I feel like my questions and discussion are conceived as a end all know it all answer. It's just conversation that is out there when someone searches for answers. It advances my knowledge and possibly others searching. or not...


...as Bruce Lancaster said, if you have the right answer no one cares. But if you have the wrong answer, people will bend over backwards to tell you how wrong you are.