Factory service manuals can be purchased online directly from Mercedes:
StarTek W123 online service manual
Mercedes-Benz Classic Center technical literature
All information presented herein is purely for informational purposes only, I assume no liability for your or anyone else's actions. All procedures and adjustments in this guide are to be performed AT YOUR OWN RISK
. The pump can only be properly calibrated by a Diesel injection specialist on an injection pump test bench, this is not intended as a DIY at home pump calibration guide. Getting your engine into good running condition and installing an exhaust temperature gauge (pyrometer) is STRONGLY recommended before
you contemplate touching any injection pump internals. If you believe any of the following information to be incorrect please make a post or contact me through the forum PM system and it will be corrected asap.
Pyrometer, aka EGT gauge
If you skip installing a pyrometer you risk major damage to the engine and turbo from high combustion heat.
Extended WOT of more than 10-20 seconds can create combustion temperatures high enough to damage the engine. This damage is not instant, its cumulative. The longer you run hot the more damage excessive temperatures will do and it won't be obvious there is a problem until its too late. 1250*F (675*C) is a safe limit for continuous
output, 1400*F (815*C) is acceptable for short intervals
(under 5 seconds).
A gauge, amp, harness and probe can be purchased for around $250 from many sources, eGauges
for example. ISSPRO is one of the best and they make a color-coded gauge for easy interpretation on the move. VDO makes a good gauge as well, but its backlighting is poor.
There are two methods of installing a pyrometer pre-turbo, bottom and top.
Post-turbo installation is not recommended for any vehicle.
Too many variables can drastically affect the measured temperature. There is no way to determine a safe temperature under different driving conditions and with different vehicle configurations.
The probe cannot be installed in the EGR port, the probe will not see any exhaust flow.
This method requires removal of the air filter assembly, CCV oil drain tube, EGR, turbo, exhaust manifold and intake manifold. It cannot be done with any of them on the engine. You will need a new manifold gasket (shared between the two manifolds), turbo flange gasket, turbo oil supply gasket, oil drain tube o-ring, CCV oil drain tube o-ring and EGR gasket.
For the steps on removing the manifold assemblies I suggest buying a factory service manual: StarTek W123 online service manual
Drill and tap the exhaust manifold for 1/4NPT and install as shown.
This method risks damage to your turbo and is not recommended!
Remove the air filter box.
Start the engine.
Have an assistant revv the engine to 2000rpm while you drill the manifold as shown.
Keep the engine revved. Coat the 1/4NPT tap with thick grease and cut the threads.
Boost pressure, air filter and exhaust
First off, more is not always better
The maximum useful boost pressure is determined by four factors:
1: How much fuel you're injecting (Exhaust gas temperature)
2: If you cool or supplement the charge air; Intercooler, water injection, nitrous, etc
4: Pre-turbo exhaust pressure
A pre-turbo exhaust manifold pressure (EMP) gauge is very recommended to help determine the ideal boost pressure. The "no visible exhaust smoke" method works, but its like trying to assemble a jigsaw puzzle without the box picture.
An EMP gauge can be built by installing a brass ferrule fitting in the manifold before the turbo and using 2' of 1/16" copper tube (to cool the exhaust) with a standard boost gauge. The EMP gauge should read 2x that of your boost gauge for adequate measuring range.
When boost pressure is excessive
, drive pressure will be higher than 2:1 to boost pressure. This is caused by a lack of fuel to spin the turbo fast enough. Drive pressure higher than 2:1 has two major effects, it drastically increases exhaust temperature
and increases engine pumping losses
. Both increase stress on the engine and reduce
The perfect ratio is 1:1 but 1.5:1 is also very good. You have found your ideal boost pressure when your turbo is working in this range and there is no visible black smoke from the exhaust.
Some examples of boost pressures I recommend for the OM617 series.
These are not guesses. They are based both on airflow calculations and real-world trial and error.
Stock engine: 11psi
Stock engine with an intercooler: 8psi
Rack limiter removed without
an intercooler: 15psi
Rack limiter removed with an intercooler: 13psi
Note: These boost pressures are at sea-level (14.7psi-absolute). If you live above 4000ft elevation you will need more boost to make up for the lower atmospheric pressure (For example, Denver's barometric pressure is 12.1psi).
Here is an airflow calculator to help you determine the boost you need (its already programmed for a factory-stock OM617a): Not2Fast: Turbo Calculator
Altering the air filter and exhaust systems do not provide any
benefits in power or economy.
The stock intake is already a true cold
air intake and the filter flows efficiently to 400cfm.
The stock mufflers are a straight-through, unbaffled, design and the diameter is already large even compared to modern cars.
Installing an aftermarket "cold" air intake, installing a larger diameter exhaust and/or removing the mufflers will produce a 0hp
change in power. The only change they will produce is noise
Valve cover nuts: 15Nm
Camshaft bolt: 80Nm
Chain tensioner cap: 90Nm
Camshaft timing is an important factor in both engine performance and efficiency. Late timing will prevent the engine from fully charging and evacuating the cylinders of air and exhaust, causing poor performance, high EGTs and smoke.
The chain and sprocket should be inspected during every valve adjustment service.
On both OM61x and OM60x engines, remove the valve cover and rotate the crankshaft clockwise (ONLY
) until the mark on the camshaft bushing lines up with the static mark on the camshaft tower.
Once aligned, check the marking on the crankshaft dampener. A pin identifies #1 TDC, the arrow on the engine block identifies true #1 TDC. The difference is your chain elongation/wear.
A normal chain will measure 2-4* ATDC, a worn chain 5-8* and a very worn chain 10*. At 11* the chain, tensioner rail and tensioner should be replaced.
If your chain is 18* or more ATDC or before
TDC, there is a major problem that must be corrected.
Inspect the camshaft teeth for wear. If they have a sharp or jagged end you need to replace the camshaft sprocket, injection pump timing device and crankshaft sprocket as well as the timing chain.
Offset keys are available to correct minor wear and tolerance differences up to 10* of crankshaft angle.
Offset keys are sold in camshaft angle
. Therefore a 3* key will correct for 6* of chain elongation as measured at the crankshaft.
Valve timing should never
be corrected where timing would be advanced of crankshaft TDC!
The chain tensioner must
be removed prior to camshaft sprocket removal, failure to remove the tensioner may damage the guide rail.
The thermostat housing must be removed to access and remove the tensioner.
First remove the spring and then the tensioner itself.
After tensioner removal, the camshaft sprocket may be slid forward to the point just before complete removal from the camshaft to exchange the woodruff key.
Valvecover nuts: 15Nm
Adjustment and lock nuts: 14mm
Adjustment must be performed at a maximum
interval of 14,000 miles. I suggest an interval of 10,000 miles.
Valve adjustment is required maintenance of all OM61x engines.
Ignoring the adjustment interval will cause hard starting, rough idle, black smoke, high fuel consumption and high coolant temperatures.
If ignored for a significant length of time, valve face heat damage and excessive camshaft lobe wear will occur.
) Valve clearance at 20*c or below coolant temperature
Intake: 0.10mm (0.004"), 0.015mm for lasting ambient temperatures below -20*C
Exhaust: 0.30mm (0.012")
) Valve clearance at 20*c or below coolant temperature
Intake: 0.10mm (0.004"), 0.015mm for lasting ambient temperatures below -20*C
Exhaust: 0.35mm (0.014")
OM601/602/603/604/605/606 engines have automatic hydraulic valve lash adjusters and do not have any possible clearance adjustment.
Do not adjust the valves if the engine temperature is above 20*c or within 15 minutes of operating the engine.
Use a deep 27mm socket and ratchet to rotate the engine. Do not use the starter to "bump" the engine or the power steering pulley to rotate the engine (If you could, the belt would be WAY too tight!)
Place the feeler gauge between the camshaft lobe and tappet pad when the lobe is pointing up and to the oil rail
as shown below.
Lubricate your feeler gauge with oil prior to use.
Correct adjustment is achieved when your feeler gauge has stiff drag required to slide it between the cam lobe and tappet.
The next gauge size up should not be able to fit between the gap and the next size lower should have very little drag.
Replace the valve cover gasket after every use.
Print this layout to assist you in keeping track of the valves that have been adjusted.
With the #1 cylinder's exhaust valve in the correct adjustment position; From front to back (1 through 10), the valves are adjusted in the following order.
1, 6, 4, 2, 8, 3, 9, 7, 5, 10
Delivery valve holders: 45Nm
Injection lines: 25Nm
Towards the block: Advance
Away from the block: Retard
Correct injection timing is critical to good engine performance, fuel economy and EGTs.
Too early (advanced) and your engine will rattle like a bucket of nails while putting huge stress on the headgasket from the pistons working against
Too late (retarded) and your engine will smoke white/gray, stumble when cold and have very high EGTs at full load.
Stock timing is 24* BTDC. This is great for the stock engine, but anyone increasing fuel quantity on the stock injection pump will see high EGTs at full load from the long injection duration.
26* BTDC is great for those maxing out the stock injection pump. A tired engine may intermittently misfire when cold after the glowplugs cut off but this will not cause any harm.
28* BTDC is the furthest that timing can be safely advanced without significant risk of headgasket damage.
Advancing the timing beyond stock gives the fuel a longer time to burn and allows for the longer injection duration naturally associated with increasing fuel injection quantity. That puts more power into the crankshaft and less heat into the exhaust.
1: Set your engine to the desired base timing using a 27mm deep socket
on the crankshaft nose. DO NOT use the power steering pump pulley to turn the engine!
You must verify that the piston is in the correct cycle (compression and not exhaust) by removing the oil fill cap and inspecting the first two valve lobes to see if they are both pointing up and away from the engine. If they are pointing down you must turn the engine one complete revolution to get the correct cycle.
2: Remove the #1 injection line (17mm).
3: Remove the #1 delivery valve holder (15mm MW or 32 spline M)
4: Remove the delivery valve plunger and spring (#3 and 4)
5: Reinstall the pipe connector (#1) and snug it in place
6: Install the drip pipe tool. (Note: The "bubble method" is an unacceptable and inaccurate substitute) A tool can be home-made using a spare injection line and cutting it in a similar fashion as the tool.
7: Tie down the throttle lever wide open
8: Loosen the 3 front and one rear mounting bolts
9: Pump the priming plunger and rotate the pump in the necessary direction until the flow from the pipe equals 1 drip per second
Some effort will be required to move the pump with the injection lines attached. The injection lines may be removed if you wish but they will have to be slightly bent to reattach.
10: Lock down the four mounting bolts, remove the throttle tie-down
, remove the test pipe, install the delivery valve/spring and install the injection pipe. The engine will misfire for 30 seconds as air bleeds from the lines.
Intake manifold or atmospheric pressure compensator (ALDA/ADA)
MW left, M right.
The intake manifold pressure compensator (ALDA device) is comprised of a housing (103) with barometer unit (103b). The absolute pressure acts upon the barometer units through a port (103a) to the charge air pipe of the engine. Accordingly, the barometer units react to each pressure change with a change of length.
All movements are transmitted to the compound lever of the governor and to the control rod.
As the absolute pressure drops, the barometer units expand. The correction linkage (1030) of the units is pressed downwards and acts on the compound lever to move the control rod in the direction of "reduced quantity”.
As the absolute pressure rises, caused by a higher air and/or charge pressure, the movement is performed in the opposite direction- i.e. in the direction of "increased quantity".
When the control lever is in the idle position, the effect is approximately zero.
It is purely an emissions device to prevent/minimize the emission of black smoke, removing the ALDA will not increase maximum power.
The intake air under atmospheric pressure is further compressed by the turbocharger.
Atmospheric and charge pressure together produce the absolute pressure prevailing in the charge air pipe of the engine.
Speed at the start of charge operation
Atmospheric pressure, corresponding to suction quantity
Absolute pressure, corresponding to charge quantity
Pressure in bar
The atmospheric pressure compensator (ADA) functions in exactly the same manner, the only differences being not connected to the intake manifold (its vent tube must be open to the atmosphere) and a slightly more sensitive operating range.
Removal of the ALDA/ADA is not recommended. Unlike other emissions controls, this device is beneficial in that it significantly reduces emissions without harm to the engine's power, economy or longevity and it reduces carbon deposits inside the engine.
Black smoke is not cool.
Fuel rack travel sensor
MW left (64), M right (L7)
The control rod travel sensor is installed in the governor of the injection pump. It consists of an iron core, two coils (measured value and fixed value coil) and two short-circuit rings. It is connected to the electronic control unit by a 3-pin plug.
The coils (b) and (d) are attached to the iron core (a) which is fixed in the housing. The short-circuit ring (e) is connected to the control rod (2t) and is displaced with the control rod without touching on the bottom leg of the iron core. The fixed value coil (b) and the short-circuit ring (c) are attached to the top leg.
The fixed value coil (b) with the short-circuit ring (c) represents a constant inductance. Depending on the change in position of the control rod (2t), the distance between the short-circuit ring (e) and measuring coil (d) changes. The variable inductance produced is then compared to the constant inductance. From this the electronic unit determines the control rod travel.
This is purely an emissions control device to aid the ECU (Electronic control unit) in determining the correct amount of EGR gasses to flow to the intake manifold. If you have defeated EGR operation it serves no purpose and has no effect on engine performance.
This device is only present on 1984 California and all 1985-1994 models.