John Deere 790 PTO engaged kills engine

[tractorroadie]

Hello,

Long time lurker, tractor geek and shade tree wrench turner. I've recently acquired a 790 and 990 from an estate. Going through the basics and the 790 starts and runs like a top. Upon engaging PTO, engine immediately dies. Has to be electronic. I've ordered the manuals but won't be home for a week to get into it. I'm guessing it's a safety lockout not engaging but wanted to see if anyone else has had this issue.

990 hasn't run yet. I'm sure you'll be hearing more about that one here somewhere as well. Appreciate all the experience.

Tractorroadie

 

[dieselcrawler]

Seat switch or associated wiring is likely the issue. On my 3005 (new number on a 790) the motor dies if you get off the seat with PTO running... Maybe its as simple as seat switch wiring is dissconnected?

 

[tractorroadie]

From the reading I've done here I was aware of this switch. Seems there is a procedure to run the PTO out of the seat, but even in the seat, I couldn't get it to engage. I'm sure it's electrical because you can use the PTO engage handle like an on/off switch for the motor. Hope to get into the diagram and fire up the fluke. I'll definitely start at the seat

 

[dieselcrawler]

A fellow 790 owner posted a link to a wiring diagram in post #1 of the thread in the link below. It clearly shows wiring to the seat switch, should be of some help in your troubleshooting process.

http://www.tractorbynet.com/forums/...2-help-interpreting-wiring-diagram-using.html

Post back with any further questions and updates... Let us know how it turns out!

 

[RoyJackson]

Hello,

Long time lurker, tractor geek and shade tree wrench turner. I've recently acquired a 790 and 990 from an estate. Going through the basics and the 790 starts and runs like a top. Upon engaging PTO, engine immediately dies. Has to be electronic. I've ordered the manuals but won't be home for a week to get into it. I'm guessing it's a safety lockout not engaging but wanted to see if anyone else has had this issue.

990 hasn't run yet. I'm sure you'll be hearing more about that one here somewhere as well. Appreciate all the experience.

Tractorroadie

There were three versions of the 790, so make sure you use the right schematic for your tractor. The serial number, IIRC, is on a plate just above the rear PTO shield and the schematics go by the serial number range.
There are two safety switches to consider. One is the operator presence (dead man) switch under the seat. Just flip the seat up and it's right there.
There's also a PTO safety switch, IIRC. On my 790, it was located on the left side of the transaxle housing.
I can't recall if there was a separate neutral safety switch, or if that was part of the PTO switch.

 

[RobS]

On my 790 there is an override for the PTO seat switch. You flip the seat up and flip over a bent metal rod sort of thing under the seat. It's for running something like a PTO generator. I've never used it so I'm not completely sure how it works...

 

[tractorroadie]

Appreciate the help. I'll look at the schematic. As far as the serial number, upon checking tractor data my serial number is higher than the last option listed. So I'm assuming it was one of the last ones off the line. Bummer it's the lower HP machine, but for the price I paid, it doesn't matter. Here is the serial number if the more informed among us have a comment as to exactly what year machine this is.

 

[dieselcrawler]

On my 790 there is an override for the PTO seat switch. You flip the seat up and flip over a bent metal rod sort of thing under the seat. It's for running something like a PTO generator. I've never used it so I'm not completely sure how it works...

I knew there was an over-ride of some type, but never needed it, never looked. This has prompted me to check mine when I go down to the barn.

 

[RoyJackson]

I knew there was an over-ride of some type, but never needed it, never looked. This has prompted me to check mine when I go down to the barn.

IIRC, the override switch was used for off-seat PTO operation. I bought a wood chipper when I had the 790 and off seat use was 2 or 3 times a year...pretty handy. The 790 has been gone for 6 or 7 years...still have the wood chipper though.

 

[RoyJackson]

Appreciate the help. I'll look at the schematic. As far as the serial number, upon checking tractor data my serial number is higher than the last option listed. So I'm assuming it was one of the last ones off the line. Bummer it's the lower HP machine, but for the price I paid, it doesn't matter. Here is the serial number if the more informed among us have a comment as to exactly what year machine this is. View attachment 487008View attachment 487009

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