MTD 4P90HU

zeeter · Jun 2, 2016

I have a MTD 4P90HU engine in a Craftsman mower. It worked fine for two years, but this year I'm having trouble.

First time out it took a while to get it to start. I tried, left it for a while, tried again and it tried to turn, left it again, and eventually it worked.
Second time out it worked fine.
Third time out it simply will not start. It clicks, motor spins maybe an inch or two, and then nothing. Once in a while I can get two turns out of it. All the while I am not hearing any engine cranking at all.

I did a valve adjustment, new spark plug, added some fuel additive, and fully charged the battery. Still nothing.

Any suggestions? I keep reading about a solinoid, but I have no idea what that is or where it is.

Most I can say is that it seems to try a little harder once I charged the battery.

bertsmobile1 · Jun 2, 2016

:welcome:

Follow the thick red lead on the started down to where it bolts on to something.
That is the solenoid.
Bridge the two thick wires on the top one or both might have a rubber boot on them.
Use an old open ender, it will flash quite strongly so be ready for it and make sure you do not touch anything else with the spannar.

If the engine spins freely then the solenoid or the wiring to it are bad.
Naturally clean all of the connections first and the ground wire from the battery to the mower. both ends before you pronounce the solenoid deceased and replace it.

zeeter · Jun 2, 2016

bertsmobile1 said:
:welcome:

Follow the thick red lead on the started down to where it bolts on to something.
That is the solenoid.
Bridge the two thick wires on the top one or both might have a rubber boot on them.
Use an old open ender, it will flash quite strongly so be ready for it and make sure you do not touch anything else with the spannar.

If the engine spins freely then the solenoid or the wiring to it are bad.
Naturally clean all of the connections first and the ground wire from the battery to the mower. both ends before you pronounce the solenoid deceased and replace it.

Thanks for your reply.

Ok - I'll try that tomorrow when it's light out. Question, though. Do you mean the lead from the battery or from the starter?

Also, I have read that the solenoid can be bypassed. Is that true? If so, is that safe?

bertsmobile1 · Jun 2, 2016

Yes bridge between the heavy thick wires from the battery to the solenoid & the solenoid to the starter.
The solenoid is nothing more than a switch, a big switch, that can handle 200 Amps.
have a look at the ends of you wrench when you have finished jumping it
So no it can not be bypassed .
In fact nothing shuld ever be bypassed except for the purpose of diagnosing if it is working or not.

zeeter · Jun 6, 2016

Update. Ordered the solenoid from Sears the other day. Should be here soon. Cannot find the solenoid on the mower to replace it so it looks like I'll have to flip it. There doesn't seem to be any access to it from the top.

Rivets · Jun 6, 2016

The positive battery cable runs directly to the solenoid, just follow the red wire. I'm betting it is under the seat, remove the battery and case.

bertsmobile1 · Jun 6, 2016

Rivets said:
The positive battery cable runs directly to the solenoid, just follow the red wire. I'm betting it is under the seat, remove the battery and case.

And I would be guessing that too.

Of Course if Zeeter had told us what mower the engine was fitted into we could hav told him for sure but that would be way too easy

zeeter · Jun 7, 2016

bertsmobile1 said:
And I would be guessing that too.

Of Course if Zeeter had told us what mower the engine was fitted into we could hav told him for sure but that would be way too easy

It's a craftsman. I don't have the model number in front of me, but if it isn't under the battery I'll get it. Had it the other day when I figured out the engine model but seems I misplaced it.

ILENGINE · Jun 7, 2016

Mtd had a habit is bolting the solenoid to the top of the rear hitch plate on their riders. Can be accessed through the hole after removing the battery and battery box. Makes it really fun to diagnose the solenoid issue when you can't get to it with the battery connected.

zeeter · Jun 8, 2016

No luck with the solenoid. I wired it, put everything back in. Now it won't even click. Can't imagine that I did anything wrong as I wired it exactly the way it came off. Battery is good. I fully charged it last week and it sparked when I accidentally checked on the solenoid wiring while still attached to the battery. There's two plug ins - one orange and one black that I put back where they go.

Not sure what else to check. I cannot imagine the problem is with the starter as it has only been started about 20 times in two years.

MTD 4P90HU

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