Repairs Scag Tiger Cub Interlock Module

[rickmrickm]

Hi,
I'm new here (and to this) so my apologies if I do something wrong.

I have a Scag Tiger Cub that has developed an intermittent problem that I'm chasing down.

The mower starts fine provided the safety switch conditions are met. Everything runs great, and after half hour or so will shut down, no warning, just simply mowing a straight line. No sputter or misfire... it's just as if I turned the switch off... dead. If I crank it to restart, it just cranks... no fire. I know... check for spark... I didn't get to that, having only 2 hands. If I let it sit for an hour or so, crank it... it will start up again, and repeat the whole thing. And it always seems to happen when I'm at the far end of the property. I assumed if it was fuel based it would give some warning like sputtering before dying. Maybe I'm wrong here.

I read something about the "white wire in the main harness"... if it's grounded, the engine doesn't run. Today when the problem occurred, and after its hour sit, it started. While running I checked the white wire with a voltmeter... black to frame ground and red to the white wire... zero volts. So, I question the validity of the "white wire grounded = no run" theory.

I'm questioning 2 things... fuel... there is a filter between the fuel tank and the fuel pump. After the fuel pump it's a straight line to the carburetor. I put a clear filter in that line, to be able to see if the pump is pumping... seems to be.

The other question is the Interlock Module... a "black box" with 8 wires. I can't find anything of technical value on this module... I'd love to find a schematic!!

Does anyone have any technical info on this module? Like what's supposed to be on what wires, when? I'm half tempted to get hold of an old one and dissect it to a schematic. But maybe someone already has info on this.

Another thought was... are these known for float bowl needles hanging up? (I'm assuming there's a bowl/needle setup) If the needle sticks in the UP position, could I be using a bowl-full of fuel, then not refilling the bowl?

Well, I'm really interested in knowing what some of you who are more familiar with mowers than I am have to say.

Thanks,
Rick

 

[Mad Mackie]

Get the machine model and pin numbers, go to Scag.com at the bottom of the page click on manuals, Tiger cubs are in the archive, find your machine pin number, click and download the manual for your specific machine. In the manual are wiring diagrams specific to the engine options.
A schematic for the electronic control module is not in the wiring diagrams and more than likely not the cause of your problem.
A few suggestions:
Clean the vents in the fuel caps.
Remove the blower housing from the engine, clean the cooling fins and under the flywheel.
Check the voltage at the battery with the engine a full throttle.
Clean the battery terminals.
Disconnect the positive battery terminal and disconnect, clean, inspect and reconnect each and every electrical connection in the electrical system.
Under the keyswitch panel there are three connectors. The yellow wire connected to the rear of the keyswitch on a separate terminal is the charging system output to the keyswitch.
It is best with any machine, but particularly Scags, that you post the machine model and pin numbers so those of us that may help you will know the specific machine that you are asking about.

 

[rickmrickm]

Thank you, Mad Mackie, for the suggestions.

My machine is, but I'm unsure what "pin number" is, maybe it's one of these:
Model STC48V-24BS
S/N B5001813

Its Engine is:
Briggs & Stratton 24HP Gas
Model 446677, Type 0127 B1 Code 051014 YG

You steer me away from the module as being a likely culprit. I'll take that as experience.
You've also given me a shopping list of things to tend to which I will, hopefully one being the cause.
I have the manual already, and while it has a typical (vague) wiring diagram, I'd still like to know what the circuit is within. If I end up dissecting one, I'll make it known here. Maybe someone else shares a curiosity.

Thank you for the to-do list!
Regards,
Rick

Get the machine model and pin numbers, go to Scag.com at the bottom of the page click on manuals, Tiger cubs are in the archive, find your machine pin number, click and download the manual for your specific machine. In the manual are wiring diagrams specific to the engine options.
A schematic for the electronic control module is not in the wiring diagrams and more than likely not the cause of your problem.
A few suggestions:
Clean the vents in the fuel caps.
Remove the blower housing from the engine, clean the cooling fins and under the flywheel.
Check the voltage at the battery with the engine a full throttle.
Clean the battery terminals.
Disconnect the positive battery terminal and disconnect, clean, inspect and reconnect each and every electrical connection in the electrical system.
Under the keyswitch panel there are three connectors. The yellow wire connected to the rear of the keyswitch on a separate terminal is the charging system output to the keyswitch.
It is best with any machine, but particularly Scags, that you post the machine model and pin numbers so those of us that may help you will know the specific machine that you are asking about.

 

[Mad Mackie]

Hi Rick,
You got the numbers correct, your machine is a 2005 production model.
As for wiring diagrams, the Scag diagrams are fairy good compared to some. Most are in color which makes tracing wires much easier.
Red is battery, yellow is charging, green is engine cranking, orange and brown are safety circuits, white is the carb mounted fuel shutoff solenoid, blue is power to the clutch and black is ground.
The electric control module is a simple logic device and when voltage is returned from a safety circuit or more, the requested condition is allowed.
For example;
To crank the engine, the travel levers, parking brake lever, the seat switch, PTO switch in off position must all be either supplying voltage to or preventing voltage to the ECM, with the keyswitch being the primary source of voltage when in the on/engine cranking position.
There are other circuits involved, but function in a similar fashion.
As for the wiring diagram, the yellow wire actually connects to a terminal on the keyswitch. The relay with the green wires is the engine cranking relay. When the safety circuits are in the correct alignment, the ECM will ground the coil in the relay allowing voltage to go to the start solenoid providing high amperage power to the starter motor. In the B&S adapter harness, the black wire is the ground for the start solenoid, the green/white is power from the cranking relay, the red B+ is from the battery positive cable. All the black ground wires are on ring terminals on one of the engine mounting bolts. This area is problematic and may need to be addressed.
I do think that your problem is more fuel and heat related.

 

[rickmrickm]

Re: Scag Tiger Cub Interlock Module ===> FIXED <===

My intermittent stall problem is fixed... thank you Mackie for your steering me away from the ECM.
Before hitting the list of possibilities you gave me, my gut began thinking it wasn't electrical, because after sitting a half hour more or less, it would restart and do the whole cycle again.
I started thinking the float bowl valve... it it stuck closed, the engine would use that bowl of fuel and not refill.
Anyway, taking the carb off (which is, in itself, no simple task), and pulling the bowl... the valve pin had some junk on it. After cleaning it and its seat, and reassemble... it started right up and mowed 3 hours without a hitch.

So... seems a sticky float bowl valve was the culprit. Boy, this Scag is an impressively built machine.

Thanks for the input,
Rick

Hi Rick,
You got the numbers correct, your machine is a 2005 production model.
As for wiring diagrams, the Scag diagrams are fairy good compared to some. Most are in color which makes tracing wires much easier.
Red is battery, yellow is charging, green is engine cranking, orange and brown are safety circuits, white is the carb mounted fuel shutoff solenoid, blue is power to the clutch and black is ground.
The electric control module is a simple logic device and when voltage is returned from a safety circuit or more, the requested condition is allowed.
For example;
To crank the engine, the travel levers, parking brake lever, the seat switch, PTO switch in off position must all be either supplying voltage to or preventing voltage to the ECM, with the keyswitch being the primary source of voltage when in the on/engine cranking position.
There are other circuits involved, but function in a similar fashion.
As for the wiring diagram, the yellow wire actually connects to a terminal on the keyswitch. The relay with the green wires is the engine cranking relay. When the safety circuits are in the correct alignment, the ECM will ground the coil in the relay allowing voltage to go to the start solenoid providing high amperage power to the starter motor. In the B&S adapter harness, the black wire is the ground for the start solenoid, the green/white is power from the cranking relay, the red B+ is from the battery positive cable. All the black ground wires are on ring terminals on one of the engine mounting bolts. This area is problematic and may need to be addressed.
I do think that your problem is more fuel and heat related.