Eengine automatically revs up at starting?

[gabby]

This is sort of a survey.

Background: I recently bought a new John Deere 4520 and the only complaint I have is the engine automatically and immediately revs itself up at starting to about 2000 rpm before dropping back to whatever the throttle setting happens to be. There's nothing I can do about it and it worries me.

JD says it's to blow the soot out to meet emission requirements. I think it's bad for the engine to rev up before the oil has a chance to circulate.

Survey question: Do the new Kubotas do it?
Thanks,
Gabby

 

[ronjhall]

It may have something to do with the Turbo.
My Kubota is not turbo and does not rev up at start.

 

[JerryG]

<font color="blue"> It may have something to do with the Turbo. </font>
The turbo shouldn't have anything to do with it reving at start.

 

[DmansPadge]

Most automotive engines do this. If that is the correct action that JD wants, I wouldn't worry a bit. A lot of people do not warm up their engines before use. I NEVER use my tractor, truck, car, etc. until it registers on the temperature gauge. The worse thing in the world for any engine is a cold start. Just let that baby idle a while before use and I think you're gonna be just fine.

 

[B2400]

Do the new Deere's use a fly by wire throttle? If it's a mechanical throttle, I don't understand how this could happen as diesels don't use air flow to govern throttle like a gasoline engine. Diesels use fuel flow to regulate RPM. Have you contacted the dealership to see if this is normal?

 

[stevenf]

Mine is a Kubota M9000 turbocharged and intercooler does not rev up at all during startup; set the throttle stick a little above all the way slowest, heat glow plugs couple of seconds, start engine. Purr!
Steve

 

[jeffmazz]

I don't know of any Kubotas that do what you described.

You might want to consider running a synthetic oil after break in.

Jeff

 

[gabby]

These are new engines built by JD to meet the new emission req's coming into effect in the future. I'm wondering if Kubota will have to use a similar technique or are their engines already in compliance? This is how it works, per JD:

"During starting, the rack that controls the individual fuel injection pumps is held in the fuel delivery start notch (max fuel with timing advance) until the governor pulls it into the position needed to run at the speed commanded by the throttle. To ensure a good start, especially in cold weather, JDPS designed the rack magnet to hold the rack in the start notch until the govenor overcomes the magnet at approx 1800rpm. This RPM can vary by +/- 300 RPM. "

I don't know what they're saying but I sure would like to disable it!
gabby

 

[cp1969]

As far as I know, all mechanical injection systems start at full throttle, regardless of the position of the hand throttle lever. I would also suspect that the electronic injection systems use software to accomplish the same thing.

The reason why is because the throttle lever is not actually connected to the "rack" in the injection pump; the governor is. When one shuts the engine off, fuel is cut off to the rack, and the engine starts to slow down. The governor senses this and applies more and more "throttle" (rack movement) to try to get the engine to speed back up to its commanded setting. But since there is no fuel, the engine continues to slow and the rack moves to it's wide-open position, where it stays until the engine is started again. This can be confirmed by the "surging" sound when the engine starts. The engine starts at full throttle and as soon as the surging engine goes past the commanded rpm, the governor brings the rack back to the rpm position commanded by the throttle linkage.

Sorry to be long winded about this, but injecting the maximum amount of fuel is the best way to start a diesel and I'm reasonably certain they all do this. Listen for the surge the next time you start up.

 

[Youare]

My Kubota L3000DT on a cold start will rev beyond the throttle setting for a few seconds. It seems the longer I allow the glow plugs to warm the more pronounced this rev up is. After the engine is warm it is not as noticable but there is a slight surge of RPM when starting.

I figured it is supposed to do that, however I do agree that it seems it woul;d be better for that to happen after the oil pressure has come up a bit. I guess if it really bothered some people you could crank the engine over a bit with the kill switch activated.

Keeping a good quality clean oil in the tractor is probably the best counter measure.

Randy