John Deere Full Throttle

John_in_TN · Feb 23, 2011

jhunter124 said:
Bad news. It did it again today when it was down to 25 last night. I am about out of ideas, short of spending a lot of money to have it fixed. I am going to buy a service manual, I figure I will need it anyhow, and see if there is something I am over looking. I know that nothing is broke because after the initial trouble it will work perfectly for the rest of the day and works fine when it is warm. Do these things have a high idle setting when they are cold that could be sticking? Any last thoughts before she goes in to the shop?

Yes, if temp is a little below freezing they should automatically accelerate to about half-throtle immediately after starting, and stay there for 10 to 20 seconds, then return to normal idle.

crashz · Feb 23, 2011

Curious to see how you are starting it too.

When you start it, do you have the hand or foot throttle up? What happens if you start it cold at idle? Does is rev up on its own? If it starts and idles fine, does slight amout of throttle stick?

Just a guess here, but if it starts at idle and the throttle seems to stick in place, I would think that the rack would be sticking. This could probably be repaired by a deisel shop for a lot less than the dealer.

If it throttles up on its own entirely, I would suspect that cold idle circuit.

Good luck!

jhunter124 · Feb 23, 2011

When I start it the hand and foot throttle are at idle and all of the linkage is free and not binding. When it is below freezing as soon as it starts it goes to full throttle, pegs the tach. I engage and disengage the clutch to drop the RPMs ( I am afraid of the motor blowing) and after about 20 seconds it returns to normal idle, about 1000 rpm and runs fine no matter how many times I turn it off and on during the day. I didnt know that there was a cold idle circuit and that would make since as the culprit since when outside air temp is above freezing I have absolutly no problems. I have even tried starting it at 1/3 throttle, like the manual says, and still have the same result. Any idea how to the cold idle circuit works or how to disable it to see if that is the problem?

I have been adding a cetane booster that is supposed to lubricate and remove moisture since the problem started and I have no water in the seperator bowl.

kjung17 · Feb 23, 2011

A block heater will heat his coolant and may solve the problem. Have you considered heating the injection pump with a hair dryer or light bulb? That would allow you to localize the heat and isolate the problem. I did a search for bulletins on your problem and it came up empty.

Looking at the parts section, I see that this unit is equipped with a throttle position sensor. You could try to start it with the sensor unplugged. Or better yet, remove it and test it with a DVM then freeze it and test it again.

jhunter124 · Feb 23, 2011

I tried a space heater under the injection pump for about 30min and it didnt seem to help. But I was heating the fuel and if it is sensing cold coolant I didnt heat the right stuff. I thought about a block heater and might go that route but for now I want to try to fix it. I havent ordered the tech. manual yet so if anyone has diagrams or schematics let me know. Thanks.

Where is the throttle position sensor? I will give that a try on friday.

kjung17 · Feb 23, 2011

Throttle sensor is item #18, assuming HST. PRT machine has no sensor.

The more I ponder this situation, the less confidence I have in the TPS being the problem. I am thinking the TPS is just an input device for the HST controller and likely has little effect on the fuel delivery. It wouldn't hurt to test it anyway.

A quick call to an injection pump service facility may shed some light, also.

jhunter124 · Feb 25, 2011

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?

kjung17 · Feb 25, 2011

All of my information comes, directly, from the operator and technical manuals. I have not located a component technical manual for the Yanmar. The cold start advance will, certainly, increase your RPM. It should not "peg" the tach. Running a cold engine at anything over 2100 or so seems dangerous. I'll be in the shop tomorrow on some personal business. I'll try to remember to see if there is anything on Service Advisor. :thumbsup:

jhunter124 · Feb 26, 2011

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.