RPM drops after throttle opened: Diesel Fuel Lubrication Engine Additives  -- Tractor Maintenance Discussion Forum and Review RPM drops after throttle opened: Diesel Fuel Lubrication Engine Additives -- Tractor Maintenance Discussion Forum

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Discussion Boards > Active Subjects > Messages as Posted > Diesel Fuel Lubrication Engine Additives Forum

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 01-26-2003, 15:41 Post: 48195
Paul_in_NS



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 RPM drops after throttle opened

I have a 1988 JD855 with 1700+ hours on it. Since I got it 2 years ago it has had an odd hesitation when opening up the throttle. The revs increase as you would expect and then sometime after a few seconds to about a minute they drop back again. Advancing the throttle further accelerates the engine without any further hestitation or drop in revs.
Back in the summer I tried a different board (hadn't found this one yet) and got afew suggestions which I followed. I have changed the air filter and fuel filter. I also checked the throttle linkage which appears to be working smoothly and the handle does not back off as the revs drop. After all that the engine behaves exactly the same way.
Anybody have any insight or suggestions for this?






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 01-26-2003, 16:07 Post: 48203
Jeff Earthwerks Unlimited



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 RPM drops after throttle opened

Does it have lift or transfer pump which could be electric or mechanical?

What color and density is the exhaust during the event?

At "first blush" sounds like it could be a faulty injector pump or worn out or leaking injector(s).






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 01-27-2003, 07:30 Post: 48236
TomG

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 RPM drops after throttle opened

If I understand the problem, there is a hesitation and then some drift near a particular rmp and the problem disappears at higher rpm's.

Jeff's comments seem a pretty good bet especially if there's abnormal exhaust. I'm off on a slightly tack for the moment. I wonder if the tractor holds a steady slow idle (800 rpm or less) and if the max no-load rpm is in adjustment.

I think I'd check if there is service routine for the governor that is appropriate for owners. Many repair manuals say that governors aren't serviceable except by specialists. Some manuals indicate that periodic lubrication of the governor weight pivot points should be done.

The difficulty here is that the problem may be what my JD FOS Engines manual calls 'speed drift,' which is a governor problem. It would be good to eliminate that problem from consideration before chasing exotic possibilities, but it might take a diesel shop mechanic to say the governor is OK for certain.






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 01-27-2003, 08:20 Post: 48241
Billy

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 RPM drops after throttle opened

"The revs increase as you would expect and then sometime after a few seconds to about a minute they drop back again. Advancing the throttle further accelerates the engine without any further hestitation or drop in revs"

This part sounds like the friction disks need to be tighten on the throttle. Even though you say "the handle does not back off as the revs drop", it would be so slight I doubt you could notice.

Billy






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 01-27-2003, 08:33 Post: 48244
Art White



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 RPM drops after throttle opened

Yours is not a major problem yet unless it is a 500 rpm drop. I do beieve it is just a lazy govenor. Many engines will run off a couple of hundred rpm when you do what you said. If you were to gradually bring it to full throttle slowly increasing it will it still do it?






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 01-27-2003, 15:59 Post: 48264
Peters

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 RPM drops after throttle opened

My 955 would do the same If I was at PTO throttle rpm. I was convinced that it was the friction disks as at max throttle it would back off slightly and I would have to move it back up. (955 is the same tractor with more HP).
Peters






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 01-27-2003, 16:26 Post: 48268
Paul_in_NS



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 RPM drops after throttle opened

Thanks for all the the responses.

Jeff - There is no lift or transfer pump as far as I know. The exhaust just makes the usual little puff when accelerated but nothing at all when it drops. Most of the time there is no noticable exhaust except when it is really lugging (not often).
TomG - The manual calls for an idle speed of 1450 which is what it is. It holds that jsut fine.
Based on the other comments, I think I am going to start with the throttle friction plates before getting involved with the governor options. I've lived with it this long I think I will finsih the winter as is and get to it in the warm weather. I just spent 5 hours clearing 4"-6" of slushy snow off the driveway (1 kilometer long) with the loader, the snowblower wouldn't touch it.

Paul






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 01-28-2003, 05:16 Post: 48306
TomG

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 RPM drops after throttle opened

Paul: I know the old slush out the chute problem. Fortunately it hasn't happened here this winter, but there is freezing rain forecast for Saturday. Generally my blower will throw slush 10' or so and doesn't clog too often unless I clutch the pto before the auger is cleared. I've never tried various 'non-stick' sprays you sometimes hear about. Usually my loader does the job OK when the blower doesn't.

I asked about the slow idle because a gimpy governor sometimes will show up at slow rpm's. Many manuals spec for both max and min no-load rpm's, and each can be adjusted. 1450 rpm sounds like what is called a fast idle for many engines and a min no-load would be less. Many diesels won't warm up at much below 1500 rpm or so.

I think most engines can be expected to hold steady speed at lower rpm's and there may be specs in repair manuals rather than owners' manuals. It's often good to give an engine a few minutes cool down at low rpm's after hard runs.






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 01-28-2003, 12:04 Post: 48317
Jeff Earthwerks Unlimited



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 RPM drops after throttle opened

Lift or transfer pump: From my experience there are two fuel delivery system types:

a. Lift or transfer pump which ususally indicates that the fuel tank is lower than the fuel system and thus needs to "pushed" or "pumped" or "transfered" to the injector pump. The pump may take the form of the old-fashioned lever-and-diaphram type fuel pump driven off the camshaft.... or....an electric motor/pump assembly or an in-line solenoid push/pull type

or

b. Gravity feed whereby the fuel tank is higher than the injector pump therefore not requiring pumping per se.
The fuel line is plumbed to the primary filter.







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 01-28-2003, 13:24 Post: 48327
Art White



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 RPM drops after throttle opened

I would be curious as to if the lever is actually coming back. Many of the diesel engines will surge out beyond on the govenor and then settle back. The newer stlye pumps normally do not do this. Many will do this and I wonder if any action is to much unless the lever is actually moving back.






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Discussion Boards > Active Subjects > Messages as Posted > Diesel Fuel Lubrication Engine Additives Forum

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Art White 3 | Billy 1 | bullworker 2 | Jeff Earthwerks Unlimited 2 | Paul_in_NS 3 | Peters 1 | TomG 4 |




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