startup surge on a JD tractor?

[Scrappy]

I used to work at a JD dealer in my hometown about 10 yrs. ago, and I noticed that alot of the tractors would surge on start-up. It was like the throttle was held wide open while cranking and as soon as it would start it would rev for a second and then drop back to normal idle. From what I observed, the bigger the tractor, the more aggressively it does it. Is it a start-up enrichment circuit or what.

 

[J DeMaio]

Hi:



I've noticed this on the 30, 40, 50, 55 series with the 404 or the 466 engine with the inline Bosch pump. I thought our dodges always did this as well. They both smoke a lot on startup and rev when first started. At least my truck revved more when it first started than when it sits there to idle. I can't tell you why they do this though.



John

 

[Gonzo 1066]

JD pump at startup

The pump opens up to full rack to help start the engine. The pump goes back to normal throttle controll when oil pressure reaches the injection pump. This feature helps to start the engine when it is cold out. The newer JDs start like any of the other diesel engines built in the world. Seems JD lowered the compression on those early 466 engines and then found they were hard to start that way. Hence the overfuel startup. On a very cold day I always got nervous every time I turned the key.

 

[EMD Diesel Power]

My '96 would always rev up during a cold-start in below-zero weather. It never did this when it was above zero, if the block heater was plugged in, or if the engine was warm.



I just got around the problem by keeping my foot on the throttle during a cold/cold startup... 1/4 way or so... . kept it at 1000 RPM for about 5 seconds and then let it idle on its own.



A couple of times I just let it go on its own without the foot trick... . but I sure didnt like it hitting 1750 RPM during a cold start in 3 seconds.



Never figured out why it did this... . well-maintained engine... fired on the 1st piston up, etc. just a cold-weather quirk I guess. Only thing I could think of was stiff/cold lube oil in the P-pump or stiff/cold governor springs/flyweights.





Hehe... . looks like gonzo was thinking about what I was trying to think. The P-pumps also go full rack during startup---- cold oil/no pressure slows the response time of the rack/flyweights. Guess I've had too many shots of JD tonight.

 

[Mathew Clausen]

Spent a lot of hours running an early 80's 8640 JD - I always pulled the manual kill lever slightly when starting to control the initial revving.



Mathew

 

[Scrappy]

startup surge

other than possible wear on the cam and pump itself, will it cause any problems with the engine? I actually like it when they do that cause it sounds mean. I remember a couple of trackors that did it so bad that I thought that they were "running away".

 

[Royal]

Some Bosch in-line pumps have a magnet in the rack plug on the front end of the pump. The magnet holds the rack in excess fuel position for cold starts,until the flyweights can retard the rack. Pulling the shut off lever after the engine fires will pull the rack out and you will not get the high speed surge.