Injection pump timing on a M21 is controlled by a solenoid operated pulse valve inside the injection pump which varies the pressure applied to the pump distribution (advance) piston. The VP-20 control module monitors signals from a coolant temperature sensor, engine speed and TDC sensors, and the lift sensor located in the #4 fuel injector (needle lift sensor.) The VP-20 computes ideal injection pump timing based upon sensor signals and controls operation of the pulse valve accordingly.
The pulse valve varies advance piston pressure by providing an additional pressure bleed when it is open. The control module cycles the solenoid on and off a fixed number of times per second, varying the amount of "on'' time during each cycle in order to control the pressure bleed orifice. When advance piston pressure is reduced, injection timing is retarded; when pressure is increased, timing is advanced. Action of the pulse valve only controls piston pressure, and does not affect the amount of fuel injected.
If you do not happen to have flywheel/injection pump locking pins:
The flywheel can be pinned with a 5/16" drill bit (non-cutting side into the flywheel) to lock the crank at #1 TDC. The "O / T" mark on the harmonic balancer confirms #1 TDC because it lines up with the notch on the upper timing belt cover.
The injection pump cog can be pinned with a 3/8" drill bit through the lower pinning hole in the cog (~7 o'clock) and into the hole in the IP mounting bracket.
STATIC INJECTION PUMP TIMING:
This writeup assumes that your flywheel, camshaft and flywheel are synchronized. If you suspect that they might not be synchronized;
With timing cover removed, rotate the crankshaft toward TDC while pressing flywheel locking pin into bore (Figure 3). With crankshaft pin in place, insert the injection pump locking pin into the injection pump cog. The pin should freely pass through the cog into a recess in the injection pump mounting plate. This ensures that both the crankshaft and injection pump are synchronized. If not synchronized on new belt installation, reinstall timing belt with camshaft locked (special tool required), crankshaft and injection pump cog pinned.
If not synchronized on used timing belt, replace timing belt and tensioner and follow the above steps.
Camshaft/valve timing are not covered in this section.
Ensure that coolant temperature is greater than 68°F, and that injection pump lever is resting against idle stop (Figure 1) and not in the cold running position.
Remove expansion tank mounting screws, position tank aside and plug overflow hose, then remove support for air collector.
Remove distributor piston plug from injection pump and install dial indicator and adapter 13-5-330 or equivalent (Figure 2). Tighten adapter by hand and clamp indicator with slight preload.
Remove fan shroud and cooling fan. Fan retainers have lefthand threads. (optional?)
Rotate crankshaft two full rotations clockwise until dial indicator records highest value, then zero dial indicator.
Continue rotating crankshaft toward TDC while pressing flywheel locking pin into bore (Figure 3). Note dial indicator reading when pin engages hole in flywheel.
Indicator reading should be .0256-.0272 inch (.65-.69 mm). Optional for performance: Stock IP, 0.70-0.80mm. 12mm Cam disk, 0.90-1.2mm. Biodiesel/WVO, [to be added]
If indicator reading is not as specified, adjust pump timing as follows:
Remove pump wiring from retaining clips, then loosen 3 pump to bracket mounting bolts.
Loosen 2 pump flange mounting nuts just enough to allow pump to be rotated, then adjust pump to obtain specified dial indicator reading. Ensure that gauge pin is properly engaged in hole in flywheel when adjusting pump timing. Rotating pump toward engine advances injection timing.
When specified indicator reading is obtained, torque flange mounting nuts, then the bracket mounting bolts to 16 ft. lbs.
Remove gauge pin, rotate engine 2 complete revolutions and install locking pin, then check static timing adjustment and correct as needed.
Install new seal on distributor piston plug and torque plug to 14-22 ft. lbs., then install remaining components.
[Thanks: Frybrid, DieseiBoost]