Kioti Fuel Injection Pump Failure and Repair

Kioti Diesel engines use a Bosch style inline fuel injection pump (IP), sometimes called a "jerk" pump.  Doowan actually makes these IPs under license to Zexel, which was formerly known as Bosch.  Readers who are not familiar with these IPs should review the excellent diagrams in the engine section of Kioti shop manuals as well as the many photographs, diagrams, and descriptions in Bernty's IP web page.  The IPs for all Kioti models are generally similar except for size and the number of engine cylinders

These agricultural IPs (and also similar marine Diesel IPs) are simpler than automotive IPs because the cam (that drives the plungers) is in the block, not in the actual IP.  Also, these agricultural IPs do not have a centrifugal timing advance, as do many larger engines. So the actual IP is a essentially a row of plungers (that slide in close-fit cylinders) which are driven by a camshaft.  There is one plunger per engine cylinder and one cam lobe per plunger.  Injection timing is set by shims that raise or lower the entire IP so the cam starts to move each plunger precisely when the respective engine piston is at a specified position before top dead center (TDC) on the compresion stroke.   If an IP is properly rebuilt or if plunger gears (more later) are  replaced, the IP does not need to be re-timed assuming the shims are unchanged and it was timed correctly before.

The shims establish the when fuel injection begins (in degrees BTDC) by raising or lowering the entire IP with respect to the camshaft.  But the plungers are rotated, simultaneously, to establish when fuel delivery ends.  There is a spiral-cut channel in the side of each plunger and a relief hole in each IP cylinder; when the two align the fuel injection pressure is released and fuel delivery (injection) stops.  The length of plunger stroke between the beginning and end of fuel delivery determines the amount of fuel injected (more fuel means more power).  To rotate the plungers simultaneously, each plunger is keyed to a gear and all gears engage a common toothed rack.  This rack is moved forward or aft to deliver more (forward) or less (aft) fuel to the engine cylinders.  A system of  springs and a centrifugal  governor  constantly adjusts the rack  position to maintain a constant engine RPM corresponding to the "throttle" position.  To stop the engine, a stop solenoid (or manual shutoff) pushes the rack fully back to a position where no fuel is injected.

Ritcheyvs has been tabulating Kioti IP failures reported on TBN in this online spreadsheet.  In addition to reported failures, that spreadsheet includes links to an excellent tutorial by neches and Diesel repair shops that fixed IPs for Kioti owners or supplied the parts for DIY repairs.  If you happen to have one of these tractors that develops this IP problem, this information should save you considerable grief and cash.  Fixing the actual IP is almost trivial compared to removing and reinstalling the IP but mistakes in IP reassembly can be costly..

The main failure mode form these IPs involves broken teeth on one of the gears that rotate the plungers.  Conestoga Diesel reports that this failure mode is relatively common in agricultural IPs from many brands (this is not just a Kioti problem).  When the gear teeth break, the broken piece of tooth often jams between the rack and a gear so the rack (and all gears) can no longer move.  In most reported cases, this ocurred when the engine was shut off and the rack jammed in the off/full-aft position.  However in a some cases the rack jammed in a forward position resulting in high, uncontrollable engine RPMs.  When that happened, those engines could only be stopped by stalling with the clutch while in a high gear (gear tractors only) or shutting off the fuel supply under the hood (the only option for hydrostatic transmissions).  In most cases, the owner reported he was unable to restart the tractor after a normal engine shut off.  This failure seems limited to 2005-2008 engines; these engines have the stop solenoid on the front of the engine and an oil-fill port on the right side of the engine, just below the IP.  It is easy to test for this problem by (1) removing that oil fill port plate, (2) turning the key switch to "on" to retract the stop solenoid (or you remove the solenoid), and  (3) checking for free movement of the rack pin with your finger.  If the rack is jammed and won't move you probably have a broken IP gear tooth jamming the rack.

It is not difficult to remove and replace the IP; several owners have done this themselves.  It is also possible for  owners to replace the broken gears.  Unfortunately, Kioti only sells complete IPs (in the $1-2K range)  not replacement gears.  But there are two economical repair options.  In many cases, the gear is symmetrical (some later gears were not symmetrical) such that the gear can be removed and reinstalled rotated 180 degrees (so the bad teeth do  not engage the rack).  Otherwise, these are standard Zexel gears available from some Zexel//Bosch Diesel repair shops (see references in linked spreadsheet, above).  Obviously, any broken gear tooth debris must be removed while repairing the IP.

CAUTION-IMPORTANT: For owners who elect a DIY IP repair, be sure to keep all the parts for each plunger/cylinder set together.  Each plunger and cylinder are machined as a matched set.  The vertical dimensions of the roller tappets, plungers, and cylinders are critical to injection timing so swapping parts between cylinders can cause problems.  If you get the parts mixed between cylinders it may cost several hunderd dollars to re-calibrate the IP on a Diesel calibration bench (definitely not DIY stuff).

Kioti owner (and TBN poster) Bernty prepared an excellent tutorial with great photos when he repaired his IP.  The first page discusses IP removal and theory of operation.  His second page shous how to tear down and rebuild the IP, including some good pics of actual gear tooth failure.

As a final observation, some owners with early IP failures had a second failure with a brand new IP from Kioti.  This  suggests that there was a period when a good number of IP gears weren't adequate.  So if you ever have to do this repair, a set of new gears from a reliable Diesel shop (probably under $200) may be the smart move to avoid future recurrence. 

Since the above writeup, the IP on my 2006 DK45 failed.  Based on my experience, (1) Remove the loader if at all possible. (2) get ner IP gears (actually called control sleeves) and a new intake manifold gasket for the  before starting.  (3) Find a way to hold the hood up or remove it (I tied mine back to the ROPS with a rope).  (4) Use care not to lose or break fastners.  (5) Don't rush, take cell-phone photos along the way to assist re-assembly.