# John Deere 4850 loads up horrible on startup, but when it cleans out it runs great??



## JD4850 (Apr 20, 2020)

I am a newbie to this forum and could use some expert advice if it's out there..

I bought a 4850 last year and during spring till I started to lose coolant out the overflow. Tractor had no starting issues or power loss. Tore it down this winter turns out it had 5 bad injectors, most of the intake valves were leaking and had a blown head gasket. Had all the injectors rebuilt , sent the head to be milled and rekitted with valves and new head gasket. Put it all back together and fired it up. 
This is where it goes funny. The tractor will start up but will take forever to clean out. It chokes so long on startup and then when it starts to clean out it sounds like the pump is gonna run away and then comes back down and runs absolutely perfect. Slow idles just fine , fast idles just fine and is super responsive.The pump was never taken off the tractor only removed the head to send it out to be reworked. I haven't had a chance to get it under a load to see how she acts since Spring time in Northern Ohio is pretty wet yet, but I drove it back to the farm from our shop which is a 7 mile ride and the tractor ran perfect. 
I would love some ideas on what the problem could be. 
Thanks for helping


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## Hoodoo Valley (Nov 14, 2006)

Welcome to the forum JD! As it turns out, we have an in house pump whisperer that'll be able to sort this out for you!


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## JD4850 (Apr 20, 2020)

Oh man that is music to my ears.


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## Fedup (Feb 25, 2014)

Most John Deere six cylinder tractors of that era used a Bosch inline injection pump. Pretty much all of them start that way. No matter where you set the throttle, when they start it's with a lot of smoke, clatter, and high revs then they settle down to wherever the throttle is set. Usually all happens within just afew seconds. It has to do with overfueling/cold start mechanisms within the pump. That is normal for them. If yours takes much longer then there may be some issues with something in the pump.


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## JD4850 (Apr 20, 2020)

I totally agree with you. We've had Deere's with this style injection pump since I was a kid and I always loved the way they start..... This is the exception to that rule. Before the new parts the tractor would roll over a few times , fire and take about 5-10 seconds to clean out and idle. It is literally between 30 and 40 seconds now and man alive does it belch smoke. I was wondering if maybe the previous owner had the pump turned up to compensate for the loss in power due to head gasket , valve and injector failures and now it is just so overloaded on startup that it has a hard time cleaning out. I had the block warmer on it and it still took a good 15 -20 seconds to clean out and it is twice as bad on a cold start.. So bad in fact that I vowed to never cold start it again. This is not the normal startup of this pump style.


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## thepumpguysc (Jan 25, 2015)

I don’t know tractor mdls.. but I do know inj. pumps.. so if u were to snap a pic of the inj pump, it would speak loads of info to me..
Fed up is correct.. on certain JD Bosch pump mdls. there’s a magnet either in the front “rack cap” or inside the pump, that u can’t get to..
If it’s in the front rack cap u can check & see.. IF ITS THERE, u could try to take a THIN piece of cardboard & put it over the magnet..
Just remember that the pump rack HAS TO slide in & out of that cap.. if it gets hung up on your cardboard YOUR GONNA KNOW IT QUICK!!
There’s actually 2 magnets GLUED into the cap..
I’ve actually heated it up & removed 1 of them & the customer, who had your complaint, was very satisfied.
Let us know what kinda pump you have & the magnet situation.. Good Luck


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## JD4850 (Apr 20, 2020)

Will do pumpguysc. I am currently at work and will be at the farm after I get off here and will send you a pic of the pump. Thank you for your time, I greatly appreciate it


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## thepumpguysc (Jan 25, 2015)

10-4 
BE SURE to snap 1 of the front.. I can tell by the looks of the rack cover if its the 1 w/ magnets.. actually I can tell u what it looks like:: its aluminum w/ a "bump out" on the end..


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## JD4850 (Apr 20, 2020)




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## JD4850 (Apr 20, 2020)

I have a couple photos on my phone I will send em as they upload


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## JD4850 (Apr 20, 2020)




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## JD4850 (Apr 20, 2020)




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## JD4850 (Apr 20, 2020)




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## thepumpguysc (Jan 25, 2015)

Nope.. sorry bud.. its not in the cap..


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## JD4850 (Apr 20, 2020)

okay. I spoke with a JD tech up here and he said to run it under a load and see how it acts and then if it doesn't clean up, may have to Dyno it to get some more clues.
Thanks for your time


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