John deere 4120 Issues

[justaacres]

Long time reader first time poster. Having my first issues with a 2005 John Deere 4120 with 900 hours and looking for some inside. I believe these two issues are related. The first issue is difficulty starting when cold. The engine will turn over and start then die. It will start again but after a lot of cranking. This tractors has always started easy before no matter the temp. The second issue is when running the engine will surge (~300 RPM) when driving with and without loadmatch on. Seem like a sensor issue to me, so I started by pulling the connector to the MFWD speed sensor. That fixed the surging while driving issue, but still had the cold start issue this morning. I have been looking for a engine speed sensor but cannot find it. Any Ideas?

 

[kennyd]

Is the fuel bowl empty when it dies the first time? Have you changed the filter and drained the bowl?

 

[justaacres]

The fuel filter was only a month old but I did replace it to be safe.

 

[4310]

Here's a link to the JD parts site. If you haven't looked there yet just put 4120 in the model search and you can find exploded views of every part on your tractor.

John Deere - Parts Catalog

 

[justaacres]

Thanks, I have been using the parts catalog. I think I may be getting somewhere on this. Tried another cold start this evening and it would not start at all. But the "good" news is it is throwing a code now. Err 08 which per the manual is a throttle position sensor out of range or not calibrated. Has anyone replaced a throttle position sensor on a 4x20 before? Looks simple enough.

 

[justaacres]

An update: I put the battery on the charger last night and this morning the Err 08 is gone. Checked the throttle position sensor voltages and they are in spec. .9 volts with the throttle in the low position to 3.5 volts with throttle in the high position.

 

[justaacres]

Update from Sunday. I cracked the return fuel line going into the tank and fuel is flowing during cranking. I'm staring to think the issue is with the fuel cut off solenoid or the wires going to it. It clicks when I turn the key on and has 12 volts to it, but during cranking that voltage drops to less then 10 volts. Has anyone had problems with this solenoid? John dere parts call it an engine performance solenoid.