John Deere Full Throttle

Don87 · Feb 26, 2011

jhunter124 said:
Got down to low 20's this morning so I tried to start it. As expected it went to full throttle, over governed speed so I stalled it. I heated the area where I found the coolant senor in the injector pump for about 1 minute and tried again. It started just like normal It did smoke more then normal for about 10 seconds but after increasing the RPMs to about 2000 with the foot throttle it cleared up and ran perfectly. So, at least I now know what is causing the problem. I looked at the online parts diagram and saw where the sensor is in the injector pump but it did not have a seperate part number so a call into the dealer is in order. As some of you suggested a block heater should get by the problem which I will probably add anyways just to make cold starts easier on the motor. Ill keep you all posted on what I find. Thanks to all for your input.

Just out of curiousity, can that sensor be removed from the pump, and does it have a gasket that could leak allowing water to enter?

jhunter124 · Feb 26, 2011

Yes the sensor can be removed from the pump for service but it cant be ran with out it. I checked the o rings and they all look good. Luckily there is no way for coolant to leak into the injection pump. If it did leak it would leak outside the motor.

Don87 · Feb 27, 2011

jhunter124 said:
Yes the sensor can be removed from the pump for service but it cant be ran with out it. I checked the o rings and they all look good. Luckily there is no way for coolant to leak into the injection pump. If it did leak it would leak outside the motor.

I wasn't looking for coolant. There is a slight possibility that water can enter from the outside, and form ice. That ice could in turn fall between the sensor actuator and the idle contol lever on the pump, thus causing the 'full throttle' problem you are experiencing in freezing weather.

The sensor is set to extend to a 'predetermined' level, but if a piece of ice gets in there, it could push the throttle farther.

That would also explain why it doesn't do it after the engine warms a little, and would also explain why heat around the sensor worked for you also.

You've got it narrowed down that far(or so it would seem), I would pull the sesor and look for water/ice in the cavity.

Jerry/MT · Feb 27, 2011

jhunter124 said:
Got home and played with it today and noticed two small coolant lines coming from the thermostat housing and just below it to a fitting on the fuel injection pump. After removing it I found a mechanical coolant temp. sensor that moves a small piston inside the injection pump. I heated the sensor, which extended the piston blocking a small port in the housing, and reinstalled everything and the tractor started and ran like normal even though it got to freezing last night. My guess (for now until the tech. manual arrives) is that the injection unit senses coolant temp and if it is below a certain level it adds fuel to increase the throttle until the motor warms up? I will try a cold start tomorrow and if I have trouble I will heat the sensor and try it again. Does anyone have experience with this type of system on a Yanmar like mine or any other motor?

You can thank the geniuses at EPA for putting emission devices on tractors. The device you have described I believe changes the injection timing in response to some pertinent temperature so as to reduce cold weather startup emissions. I believe yours is malfunctioning causing an engine overspeed. I have a NH TD95D and it has a similar device on it but it's never behaved like what you are describing.

My NH has a 5 year emission systems waranty (read injector pump) and since mine is a 2007, I'm still under warranty. Is your tractor still within the emission warranty period? If it is then talk to your dealer. If it's not, find a replacement sensor and replace it before you do some serious damage to your engine.

jhunter124 · Mar 17, 2011

Jerry,

You are exactly right. I went into a local injection pump shop and explained my problem and after some research they found the sensor I needed and said that if it is just slightly over fueling the idle circuit it will cause the full throttle problem. I ordered the new sensor ($37.00 instead of the $1500.00 rebuild john deere quoted me) and installed it the other day. The outside temp was too warm to test it so I put an ice pack on it for about 45 minutes. It started and ran just like normal. A true test will be when it gets below freezing again but not sure if that will happen this year. Thanks again to all who gave input, you saved me some cash.