Troubleshooting: engine won’t turn over, burning through solenoids?

[Billylegend]

You are right, I need to be more systematic about it. Given the history of this problem with the two solenoids I’ve already replaced after swapping the battery, starter, etc, running all the multimeter tests - and facing the same symptom (key turn, LCD display but dead silence), I assumed it was the solenoid again. But you know what they say about assuming. I appreciate the list of things to check, and I will.

I have a couple questions please:
- is there a way to safely bridge the cables/posts on the solenoid? I’ve done it before with a screwdriver and there’s a pretty good spark
- bridging from the battery to the solenoid trigger wire - which wire is the trigger wire? I assume it’s not the hot wire coming from the battery or the wire leading back to the starter. It’s got to be one of the other two?
- do you want me to take both sparkplugs out? Alternate one and the other? this is a dumb question (sorry), but why/how would the engine crank without spark plugs?

Ok, so I can rotate the engine by pressing down on the flywheel screen and turning. So “check”.

I reattached the solenoid (I had detached it to get the part number) and accidentally touched the hot battery wire to the black solenoid post wire (trigger?) and the engine cranks. So inadvertent “check”.

I tried bridging the posts using the screwdriver and along with a nice spark the engine cranks. So “check”.

I tried turning the key in the starter, and miraculously it starts again. I’m scratching my head as to what’s going on here. One day, nothing (expect LCD display), today it starts normally.

 

[Scrubcadet10]

your ground cable tight at both ends?

 

[bertsmobile1]

Crank = rotate
Fire = goes bang at least once
Sparks are fine, that is the prime function of the solenoid , to reduce the sparking from the heavy current draw
At the base of the solenoid will be 1 or 2 thin wires .
The dark colour will be a ground and the lighter one will be the power .
One or both could be switched
So check them for ground and jump from the battery cable to the other
If the solenoid trips and the engine cranks then the solenoid is fine
If neither wire is ground when all of the controls are in the starting position and neither are power then you have a cranking circuit problem

 

[Rusty Knuckles]

For safety reasons , always disconnect your black ground negative cable from your battery until you are ready to start actively testing your circuit. That will eliminate any accidental sparks .

 

[Rusty Knuckles]

Also a remote starter button works better than a screwdriver when trying to jump the solenoid.

 

[Billylegend]

Sorry for the late response, I only get to work on the lawnmower on weekends. First let me respond to the suggestions above (for which I am grateful, so thank you) and then I will share what my experience lately has been.

To @Scrubcadet10, thank you - but I’m a newbie and not sure which two ends of the ground cable you’re referring to. The end on my battery is tight and the ground spade connected to the solenoid is tight. I’m fairly sure the other ends of both cables is tight too but I’ll double check tomorrow.

To @bertsmobile1, thank you - I’m pretty sure the thin wires attached to the spades at the end of the solenoid are correct based on Sears videos and diagrams I’ve looked at. The thin white/power end is on the same side of the solenoid as the thicker red hot wire from the battery. The thin black/ground wire is on the same side as the thicker black wire with a red strip headed to the engine block. I’m sorry, I’m not sure what you meant when you said “jump from the battery cable to the other”, if you could please clarify I’d appreciate it.

@Rusty Knuckles, thank you.

Here’s what I’ve noticed lately with the mower. When it’s “cold” (been sitting), it cranks and fires right up like new. BUT, once I drive it around for a while and use it (I scoop up leaves with it lately), and turn the ignition key off, it will NOT crank or fire again when I turn the ignition key back on. As described above, I get power to the tiny LCD window but nothing else, no sounds, nothing. Like it’s dead. I’ve experienced this “cold start only” phenomenon at least 2-3 times now, consistently. Frustrated and needing to continue my massive leaf job today, I grabbed a screwdriver, turned the key and jumped the solenoid, and it cranked, fired, and started right up. I finished the job by just leaving the mower idling lightly while I emptied my leaf bag instead of turning off the ignition. As a test, once I parked it back in my shed for the day, I turned the ignition off, waited a beat, and tried turning the key again - and again, with the engine ”hot” nothing except the tiny LCD display. I bet if I try to start it tomorrow morning (cold) it might work.

One other thing I’ll mention is that I noticed that the screw holding down the solenoid to the mower frame was a tad loose today and I tightened that, but it didn’t make a difference.

Any clarifications to the questions above are appreciated, and any comments on my experience above are appreciated too. Thank you for your patience with me.

 

[bertsmobile1]

The solenoid is just a switch
It is electrically controlled and works by an electromagnet closing a pair of big contacts which are usually held open by a big spring .
This happens very quickly which avoids the creation of a massive spark as you got with your screwdriver across the top cables.

For the electromagnet to work it needs connection to both the + & - sides of the battery
On some there are 2 thin trigger wires at the base to make these connections
On others there is only a + trigger wire because it grounds via the mounting bolts / screws as the metal part of the body is not insulated from the magnet coil
This type are highly prone to corrosion making the - connection bad .
To test the single wire type you make a good ground connection to the metal part of the body then jump from the battery cable to the trigger wire .
Every time you make the connection it should give a loud klunk and if the connection to the starter is good and the starter itself is good, the engine should crank.

The single trigger wire does a full loop on most mowers as it starts from the power feed to the key switch, which is generally on the battery cable of the solenoid ( to save wire ) , then goes through fuse to the key switch then from there to the PO switch followed by the brake switch then back to the solenoid on the trigger terminal .

IF your solenoid is not activating then there are 3 switches to be tested plus the wires between them
So when you turn the key & nothing happens you need to check that you have battery voltage at the + trigger terminal .
THis needs to be done 20 or so times to verify it is working properly all the time .

The 2 trigger wire solenoids work exactly the same except the - trigger wire can also be switched .
You check that by testing for ground with the key off , the brake off & the PTO on
If you have ground in all those situations then it is just a ground wire and for the purpose of checking the + trigger feed you jump this terminal directly to the battery - to avoid any problems with the ground wire giving you wrong results
If the solenoid activates normally when the ground terminal is jumped then the ground wire is what is being naughty .