Sprinters up to model year 2006 share some similarity with the later model when it comes to ‘mysterious’ cutting-out and repeated intermittent non-start issues, this article covers specifically the earlier 4 cylinder Sprinter >2006, although some of the items covered are also common to the later model. The points covered here are some common failures and do not represent an exhaustive list of issues that may be causing problems with your vehicle. You may find at least some clues that help towards your own fault finding from the information given below.

To start a Mercedes CDI diesel engine, there must be a set of conditions met that the ECU requires to initiate running the engine.

Fuel

The fuel rail must provide an absolute minimum cranking pressure of between 250 and 300 Bar, any less and the ECU will not allow the engine to start. Causes for this pressure not to be maintained could be due to internally leaking injectors, faulty fuel pressure regulator or its O-ring seal (see covering article here), faulty rail pressure sensor, High or Low pressure fuel delivery pumps. Equally any air resident in the fuel delivery system will hamper starting. Usually the seals used to terminate the clear plastic pipes from the low pressure to high pressure pump give rise to air bubbles visible in these pipes, which is not a good sign and will need to be further investigated. It is worth noting that unlike any circulating diesel feed system, the fuel exiting the high pressure pump is not self bleeding and any air held within the rail will take some time to clear should you open the system to atmosphere (for instance if you do a poor job of pre-filling a new fuel filter at service).

It is worthy of note that the diesel pressures within the system of a running engine could be in excess of 1,600 Bar that is very capable of doing you some damage! – always use caution when inspecting and working on running CDI fuel systems.

Should at any point the measured pressure drop within the fuel rail, say if there were a serious ‘high-side’ leak or if you were to open a feed union to an injector the ECU would instantly cut the fuel delivery and shut down the engine as protection. Equally there is overpressure protection for the fuel system, where if it ever rises beyond a predetermined ‘safe limit’ the ECU operates the shut off valve on one of the three piston element heads of the HP diesel pump thus dramatically reducing delivered pressure to a safe level. This shut off device is the large tower like solenoid that extends from one element (there are three) of the high pressure pump, it has a two pin electrical connection and loom plug at its end.

‘Live data’ is the best way of determining fuel system pressures and the operation of the engines attached control devices, but obviously in a running engine. You will have to inspect the fuel system of a dead non-start engine using the functional details above as a guide. Unless you have a major fuel leak or the delivery pumps have catastrophically failed, fuel related problems are not often sudden and tend to show themselves as intermittent transient problems for a period of time before they get to the stage where the vehicle will no longer start. More often non-start problems arise from the electrical system.

A really useful link on the Sprinter fuel injection system here

Electrical

For the most part the electrical system will be the major cause of any none or poor starting issue. There are two main timing sensors fitted to the engine: Crank Position Sensor and Camshaft Position Sensor.  These relay engine positional information to the ECU so that it can determine when to accurately fire the injectors so that the engine can run.  Any synchronisation errors that occur between these two primary angle measuring devices will cause an engine to slip into limp home if running, and if stopped, the engine will not restart until it gets valid signals from both.  The cam position sensor is mounted on the top rear of the valve cover slightly to the left of cylinder 4 (rearmost looking in) and gets its positional signal from a lobe on the cam. Due to its location directly above the exhaust manifold, it is subjected to regular extremes of heat and daily cycles of hot and cold.  It is not uncommon for this sensor to exhibit thermal problems, where a cold engine will start and run fine, then once warm, would falter or not restart until cool. Replacement of this sensor is quite cheap – sub £30, and even if it does not cure any problems you may have, it is best to ‘eliminate it from enquiries’ if there are any synchronisation errors recorded.

The crank sensor lives on the block seam of the engine and gearbox bell housing, just above the starter motor, it picks up its pulses from teeth on the flywheel. Generally it is quite reliable – if you have problems starting the vehicle it is often a good quick check to watch the tacho needle flick slightly as you crank the engine. If it flicks, then this is normally a sign of an impulse from the sensor reaching the ECU. If however the tacho needle does not flick on spinning the engine over, then suspect crank position sensor problems.  It is possible this sensor can suffer from thermal problems but not as frequently seen as with the cam sensor.

The connecors and cabling to the injectors are important things to check, if any connector to any single injector becomes disconnected, then the engine will not run, equally if one injector solenoid becomes disconnected when the engine is running the engine will die.  It is a known problem for the injector wiring loom that lies under the black plastic cable tray beneath the fuel rail to have issues whereby the injector cables rub and abrade against the metal surface of the alloy rocker cover over time. Once the cable insulation weakens and any of the conductors short to ground, it has a similar effect to disconnecting an injector – the engine will stop. You can cut strips of plastic bottle and slide them under the cable tray to insulate the cable from the alloy cover to test if you suspect this is an issue.

The injector solenoid wiring can be easily checked for continuity and insulation to ground by removing the injector connectors and metering out the wires directly to the ECU under the dash.  The injectors connections are the large gauge wires on the push in connector to the far right looking at the ECU under the dash.  Release the ECU retaining springs to drop it down into the passenger footwell to make it easier to work on.

If you detect anything untoward with the wiring during your continuity checks, the first obviously place to look for broken cables and damage is to cut open the outer insulation on the section of loom that drops from the engine, over the left engine mount on its way to the rear of the battery shelf area. Here you will find the most mechanically vulnerable selection of sensor and engine management cables – be sure to check here first. Note: although not related directly to non starting, as previously mentioned in other posts, the turbo control, vacuum solenoid valve loom, hooks round the front of the radiator from behind the passenger headlamp and travels across the front crossmember. It passes the horn onward to the vac valve situated under the air box. Commonly this loom is found to be damaged or broken in the area where it snakes past the headlamp tinwork on the front panel. See here for more related fault finding detail.

If all fuses prove good, and the engine cranks but will not fire, then take a look at the ECU connectors. Remove each of the plugs and check that water, usually from a poor windscreen seal or rust-rotten screen surround, finds its way onto the ECU.  Over time the fine connectors and pins start to corrode and all manner or electrical issues ensue.  To remove the ECU plugs with lever tabs, push in the small locking pip just behind the upright grey lever, on the black part of the shell. Then bring the grey lever down over it and continue to move the lever to the horizontal in an arc, this will eject the connector from the multiplug.

I have had instances where intermittent cutting out has been due to dry joints on the PCB inside the ECU alloy box.  To check this out – once all the cables have been removed undo the six torx head screws holding the cover plate onto the pressed aluminium ECU box. Once removed, lift off the plate and remove the PCB assembly from the pressed case.  You can now inspect each pin solder joint with a magnifying glass to look for a broken or poorly soldered/corroded joints.  Often careful re-soldering of the suspect joint will provide a suitable repair, obviously if its corroded rather badly, the chances are that the multilayer board is damaged and at worst a replacement ECU could be needed (very rare).

If you ever get any code reader messages relating to ‘capacitor voltage low’ (Autel or none-Star diagnostic tools) I have always found these to be a good indication of faults connected to the CPS, and after replacement or repair to its connecting wiring, it has always fixed the problem which was originally accompanied by an engine that will just cease running for no apparent reason. My first advice would be when the only recovered code is one relating to ‘capacitor low’ then more often than not – its related to the CPS and well worth a try first!

Notice the relay on the right has a ‘pushed-in’ terminal

If the starter does not crank at all, then it is good to understand that the start command is issued by the ECU and not the key!  This is because the ECU monitors the key security module and will disallow starting unless a valid key (with correct internal chip) is being used in the ignition switch.  Any problem that displays ‘KEY ERROR’ in the dash LCD module is connected to using an incorrect key, a broken or missing key code chip, or a problem with the key reader detection coil (around the ignition switch) or the key security module itself (SKREEM).  If the key signal is valid the start signal will be actioned by the ECU. In auto versions it will also look to see if the transmission is in neutral or park.  Once an ECU start output is active, the start relay is commanded.  It lives beneath the driver seat, accessed through the flip off side panel, once caused to pull in – this puts voltage onto the coil of the starter motor, via a black with yellow tracer wire in the loom.

more clearly – the pushed in relay contact

I have seen odd instances where because of the nature of the size of the relay spades, they ‘give-way’ when pushed into the fuse board receptacle, pushing them up inside the relay case – misaligning the internal switch contact faces. Often a root cause of intermittent starting/cranking with just a ‘click’ – should obviously the battery and starter cabling prove to be in good order.  The dead giveaway here is if the headlamps stay bright and hardly dip when an attempt to crank is made, if it is not the relay and good voltage is reaching the stud terminal on the starter solenoid, then the chances are the solenoid itself is faulty and the starter would need replacement.

Inside the relay – the silver plated contacts are pushed out of alignment making for poor or high resistance switching

You can of course quickly test the starter by ensuring the vehicle is out of gear and then shorting the large 13mm power stud/nut on the starter to the smaller 10mm nut on the solenoid with a robust old spanner or jump lead clip. If the starter is healthy, then the motor should crank. If not, then you are most probably looking at a faulty starter motor.  If it does crank, and will not turn over from the key, then you will have to investigate why following the information in the above text.

I hope the above gives you a little information to help you fault find a few little known anomalies with the Sprinter and hopefully it leads to identifying  your starting issues.

Clutch replacement on any vehicle can be an expensive job, especially if you are entrusting the job to a main dealer.  Although large scale and a little mauling, clutch replacement on Mercedes models can be well within the capability of a competent DIY’er with only a limited number of tools.  In this post we shall look at the replacement of the clutch mechanism (including Dual Mass Flywheel DMF) on the Mercedes Sprinter – both older and newer models.

There are several important details often overlooked about the Self Adjusting Clutch mechanism or SAC, that the installer has to be aware of so that things go smoothly.  You will no doubt have read many horror stories on the web of people installing SAC clutch units only to find that on re-assembly they have no functioning clutch, then having to take it all apart again to do it properly!  The first thing to understand is how the clutch actually self-adjusts over its life and in this understanding it will allow you to assemble things in the correct manner, so when you put that last bolt in place you are certain things will work as they were designed.  If you are fitting used components, such as a second hand DMF (flywheel) or even a complete used clutch, this knowledge is ever more important.  You would also additionally need to know how check this if you were stripping and replacing the original clutch and flywheel from an engine only to replace it later, say if you were replacing a leaking rear crank shaft seal for instance.

You will remember from days of old that clutches on older vehicles used to have a different bite point as they aged, either right at the bottom or top of stroke depending on design.  This is not the case today with advancements in clutch technology.  Mercedes clutches and other vehicles too, now have circular adjusting mechanisms built into the cover plate and spring that move to compensate as the clutch wears, maintaining the release spring pressure and finger position.  This means that as a SAC clutch ages, it maintains the same spring operating position and ensures a constant actuating force to engage/disengage the clutch over its life.  Indeed it is almost impossible to tell if a modern clutch is ‘new’ or only ‘weeks from failing’ by the pedal position and feel alone – all thanks to the SAC.

When you purchase a new clutch kit you will almost always find that the clutch has been ‘set’, and is ready for installation. However it is always best to check that things are correct before fitting as I have known due to rough handling even new cover plates ‘spring’ into a full adjustment position – clearly fitting this as-is would result most probably in a non functioning clutch.

From the illustration above you will see the cover plate/spring assembly has an adjustment ring. (2)  Simply put, this circular ring is allowed to rotate if required a few degrees when the diaphragm spring is fully compressed (when the clutch is operated) Its rotational resting position is controlled by the combined action of a sensor diaphragm spring (5) and the main diaphragm spring (4), allowing the plate to slide round slightly, facilitating changing the pivot point of the main clutch springs as the driven plate wears. There are three small springs that pre-load the adjusting ring so that as the clutch wears the adjustment ring is forced to rotate slightly to drive what is in effect a ‘wedge’ into the forming clearances of the cover plate diaphragm spring at its pivot point, thus allowing clearances to be ‘auto adjusted’ within the installed cover plate.  More information about the SAC from LUK if you wish to view here.

The adjustment ring’s spring position can be seen to be fully extended on this worn clutch cover plate below, the photograph below that shows the adjustment ring in ‘set’ position, this is how the clutch needs to look before fitment. Always check this before installing the cover plate, even if just out of the box!  There are many expensive tools used for correctly setting the adjustment of the pressure plate once installed on the vehicle, whilst these are great to own, unless you fit clutches every day it is hard to justify their purchase, this post outlines how it is possible to carry out this work without the special setting tools.

If you are using a used clutch, or simply refitting your original plate, it is important to check or reset the adjustment ring to the ‘set’ position shown in the photograph directly above. This can be achieved in a press used between the stamped steel cover plate edges and the diaphragm springs.  If you do not have access to a means of compressing the diaphragm springs so that the adjustment ring can be counter rotated and reset, you may wish to read on, but use great care – as there is a fantastic amount of pressure behind those diaphragm spring fingers and a truly huge amount of force is needed to compress them!  The following is an emergency measure, only to be used to get you out of trouble and is definitely not by any means a recommendation.

On a solid driveway, place a hydraulic trolley jack under the rear axle of the vehicle and raise it enough to fit the cover plate, supported on three stout short wooden blocks of the same size, resting on the flange/outer lips of the stamped steel plate only, NOT the pressure plate (form the wooden blocks into a triangular formation).  Using a very large socket that will generously cover the hole in the centre of the diaphragm springs, align this with the axle beam or lower shock absorber mount – use solid wood packing as needed.  When in position bring down the jack ‘very slowly’ to allow the axle weight of the vehicle in controlled contact with the socket via the wooden packing, depressing fully the diaphragm spring, almost to the cover limit stop. (shown in cut away diagram above)  Now carefully rotate the adjustment ring anticlockwise with a stout screwdriver until it rests fully against its stop and the three small springs are fully compressed.  Once achieved, jack the vehicle once more and remove the cover plate that is now set for installation.  Throughout this procedure please consider your own safety at each step of the way!

Now you can begin to remove the gearbox and fit your clutch.

Working from ramps with additional additional 4-6 inch raising blocks if you have them, is the best way to achieve enough space to work comfortably around the gearbox, leaving yourself enough room to manoeuvre freely and eventually remove the gearbox from beneath the vehicle.  I always jack the vehicle onto ramps, this allows you to place one ramp forward and the other facing rearward, thus locking the vehicle from rolling either way to supplement the handbrake and rear wheel chocks.

Disconnect the battery before starting any work, as you will no doubt disturb the starter motor during the job. Also on later Sprinters,  W639 Vito and VW Crafter models remove the complete air box from under the bonnet, this prevents any strain on the plastic components, as the engine naturally tilts backwards when the gearbox support is removed.

Use a trolley jack to support the plate that supports the back of the gearbox near the output flange.  Undo all the bolts that hold the support plate to the chassis rails on either side, allow the jack to be lowered and removed. This will drop  the rear edge of the gearbox down a little so that the rear gearbox mounting pin can be removed and the support plate taken out from beneath the vehicle.

Using a 16mm socket remove the four propshaft flange bolts from the gearbox output shaft.  You will now have to remove the drop protection ‘horse-shoe’ brackets and the two centre bearing bolts to allow you to drop the prop sufficiently to allow you enough flex for it to be moved out of the working area to one side of the vehicle.

Now remove the gear selector cables, make sure you mark the shaft positions in the plastic ball-ends (amount of insertion) before you release them and tie them to one side. Put a latex glove under the cap of the brake/clutch shared master cylinder, before clamping off the flexible clutch hose from the chassis to gearbox. With a small screwdriver or pick, detach the hydraulic connection retainer clip from the gearbox hose coupling, keeping this in a safe place.  Pull out the hose and again tie it out of the way of the working area.  Remove any electrical connector or plug and tuck them out of harms way.

Now using at least a 24 inch extension bar and reverse torx socket remove all the ring bolts from the bell housing. There is no need to fully remove the starter motor, just let it rest in position.  It will be held in place by its thick cable. On T1N models up to 06, you will have to remove the exhaust support (2 x 12mm nuts) as this sits sandwiched directly behind the gearbox and will prevent removal unless fully removed.

When you get to the last bell housing bolt, support the gearbox centre on the hydraulic jack, remove the final bolt. From the back of the gearbox pull, the casting should now separate from the engine block.  Manoeuvre the gearbox back and lower the jack. Take the gearbox from under the vehicle.  This is a great time to check for leaks or damage/wear to the selector mechanism. Checking the gearbox oil level is easier at this point too!

From inside the bell housing you can check the rotary smoothness of the thrust bearing, this is part of the release slave cylinder mechanism and cannot be replaced on its own. If you can afford it, always replace the slave cylinder when replacing the clutch, often if you purchase a complete kit it comes as a component part.

Always inspect the centre bearing in the DMF, if this is damaged it is not available as separate part from Mercedes only as part of the complete DMF flywheel! The bearing itself is a special construction of a blind roller bearing made by INA that acts directly on the input shaft end of the gearbox, this is concentrically inserted into yet another single row ball bearing race pressed into the DMF.

Remove the clutch cover/pressure plate from the DMF, locking the flywheel with a small crow bar or broad screwdriver on the ring gear. You may have to pry the cover off its locating dowels, be aware it is heavy and it could catch you by surprise and fall on you!  Once this is out, you can inspect the flywheel face for damage. The outer DMF section of the flywheel should only rotate independently about 10-15mm in each direction at its circumference in relation to the other fixed half, any more than this indicates the likelihood of a worn DMF.  If you decide to replace this, you will need a long, large torx bit to undo the eight flywheel mounting bolts from the crankshaft. Once removed pry the flywheel from the crankshaft, it sits on a single dowel peg and can take some working to and fro to remove it.   Always inspect the centre bearing in the DMF, if this is damaged it is sadly not available as separate part from Mercedes, only as part of the complete DMF flywheel!  The bearing itself is a special construction of a blind roller bearing made by INA, that acts directly on the input shaft end of the gearbox, this is concentrically inserted into yet another single row ball bearing race which is directly pressed into the DMF.

Replacement of all the parts is exactly as the removal, although be sure to reference the ‘set’ position of the clutch before refitting.

Bleeding the clutch system can only be achieved with a Gunsons EzBleed or other pressure bleeding equipment, no amount of pedal pressing, as you would assume similar to brake systems will not work – trust me, you will be very lucky to achieve success otherwise.  Once you have a good pedal feel and the slave cylinder can be seen to be pressing the diaphragm springs back and forth fully through the inspection hole, start the engine. Now press the clutch pedal several times, you should often hear a light clunk, this is the clutch adjustment ring finding its own position.  Select a gear and test the clutch, all should be well.  If for some reason it appears as if the clutch is not fully disengaging and baulking you from selecting a gear, check your work regarding air in the hydraulic system, if re-bleeding it proves to be good, then try starting the engine in gear, handbrake on, with the clutch down, this will often by inertia, force the adjustment ring from its set position to its new working position, a second pedal press should now settle it into its new operating position and you should have a good responsive light clutch.

I hope you have found this information useful.

 
One of the 2004 long wheel base Mercedes Sprinters developed a problem where everything was fine under moderate throttle openings but once full power was called for, the van would register a fault and lock into limp home. Recycling the ignition cleared the fault, until the next wide open throttle and call for high power.

A great deal of work had been done on this particular van over a short period and most of the regular problematic contenders covered elsewhere on this subject had been dealt with. We knew we had good fuel delivery, good fuel pressure, sound boost and good induction hose-work. New sensors had been fitted on both low and high pressure points on the system and the only fault recorded was low boost.

We had previously seen another fleet operators Sprinter register low boost and discovered that the intake air filter was completely choked with muck and grime, this was not the case with this van.

Examining for mechanical issues became a primary focus as all the electrical systems were sound and cross-referring their readings on ‘live data’ proved their adequate function. In driving the vehicle with the code reader connected, we were able to see that maximum turbo boost was never achieved at full power, but was seen approaching moderate peaks at more modest and lazy throttle openings.

Often the van would perform fine unladen and fail consistently when loaded, slipping into limp home as soon as the driver tried to make good progress.

I removed the airbox and checked the vacuum pipework from the brake servo to the boost control valve and everything was in good order. I removed the supply pipe to the turbo actuator and double checked this for problems such as nicks, cuts and splits – nothing.

The lever arm to the turbo was free and this was confirmed by removing the circlip from the eye of the actuator arm and manually operating it to prove there was nothing wrong within.

My next test was to push the actuator rod back into the actuator and be certain the movement was unhindered and smooth. The next test was to block the vacuum pipe opening with a finger, allowing air to be expelled while I pushed the rod inward. Closing the gap with moderate finger pressure should be enough to hold vacuum inside the diaphragm, making a ‘popping’ sound as the rod springs back to its extended position when you release your finger. I noticed the fitted actuator was not doing as it should in that respect as it was not ‘popping back’ to an extended position. Indeed, careful observation proved that the rod was moving very slowly to a fully extended position with a finger blocking the port, indicating a failure of the internal diaphragm – probably a slight leak or pin-hole.

This would under normal circumstances been difficult to spot as it had not failed completely. The actuator still pulled the turbo lever to a fully down position once the engine was started. However the small leak meant that the on-off pulse control of the actuator, given by the Pulse Width Modulation (PWM) of the vacuum control valve, was not as it should have been – resulting in under-boost on high power call situations.

The replacement of the actuator although fairly straight forward in mechanical terms, is a bit of a fiddle to accomplish, as one of the mounting bolts is a good finger-stretch into the confines of the turbo and takes some jiggling to get the pin back into position and tighten it.

There are three 10mm bolts into the exhaust side of the turbo scroll casting. These hold the actuator support bracket and also clamp the spool cartridge face against the turbo scroll casting flange making a gas tight seal.

Once these three bolts are removed and the circlip removed from the rod/lever, the actuator can be removed for inspection. Access to the area is best achieved by removing the complete air box, the turbo intake hose and brake servo vacuum pipe. Once these components have been removed, additional removing the vertical heat plate/shield that separates the air box from the turbo assembly is essential to obtain free access to the three actuator fixing bolts – especially as one is a real swine to get to!

It is important to set the actuator arm/rod length of the replacement part to the same dimension as the original. This is critical in that it effects how the vanes are positioned within the turbo for any given actuator setting. Simply measure the new rod length to the old one and make adjustments using the 10mm lock-nut and thumbwheel provided on the actuator rod. Lock the setting once you have it and ensure the hole in the rod eye is positioned in the correct plane to accept the lever bar of the turbo once reinstalled.

Rebuild is the reverse of disassembly from this point. Once fully built, check your work and clear any remaining fault codes and then road test the vehicle. Once again boost should be available through the complete power range and it should react smoothly to engine loading, just as it did prior to the fault occurring.

Other Mercedes Sprinter turbo fault/boost related posts:

http://www.mercedes.gen.in/WP35/mercedes-sprinter-turbo-limp-home-los-diagnosis-fault-finding/
http://www.mercedes.gen.in/WP35/new-turbo-still-boost-mercedes-sprinter/
http://www.mercedes.gen.in/WP35/not-maintaining-sprinter-air-filter-can-leave-stranded/
http://www.mercedes.gen.in/WP35/diesel-mercedes-sprinter-turbo-rebuild/
http://www.mercedes.gen.in/WP35/mercedes-sprinter-turbo-blown-symptoms/
http://www.mercedes.gen.in/WP35/mercedes-sprinter-t1n-large-engine-oil-loss-leak/

Please be sure to use the comprehensive site search facility to find what you are looking for (Just enter your search term in the search box on the top right and click search) – There are many informative Mercedes posts on this this site, just waiting to be viewed!

In a recent Mercedes Sprinter engine replacement (Used engine fitment) it was noticed at the time of purchase that there was an issue with No.2 Injector seal leaking. Obviously this needed attention and there was more chance of being able to remove the stuck injector once the engine was fitted, than try to do the work on the engine prior, as it would simply move around the floor with the physical effort involved!

What I did do before fitting the engine was to get rid of all the carbon ‘Black-Death’ build-up due to the leaking injector. This involved careful chipping and clearing the cables, connectors and pipes that were buried beneath the charcoal coating. If you want a really clean and sparking job, I can recommend a none-acidic oven cleaner for a final dressing, but in this case it was cleaned to a ‘practical degree’ that fitted with the age and condition of the vehicle.

Without a doubt, if you are able to start the engine and get it warm, even loosen the clamp bolts five or so millimetres above the shoe clamp then rev the engine, what often happens is the injector gets ‘blown out’ a little under engine compression and once the carbon seal is initially broken, it can make subsequent extraction a great deal easier.  Sometimes it works – sometimes not!

In my case I knew that the engine would probably not start as the seals were in such bad condition. As I turned the engine over clockwise using a 27mm socket/breaker-bar on the crank nut, you could hear the escape of air past the injector seal on each rotation. This was confirmed by localised spraying of WD-40 onto the suspect injector and watching it bubble/vaporise as air from the combustion chamber was forced by the injector during a manual rotation of the engine. I had to proceed without heat or hot engine – always makes for interesting removal!

Obviously you will have to remove the inlet manifold upper half and also the engine cover if fitted before you can gain access to the injectors. It is important to plug all the intake tracts to prevent items such as the bleed off pipe spring clips finding their way down there etc…

Once the engine was fully installed, the injector power plug was removed, the bleed off return pipe unclipped and moved well out of the way. The steel diesel supply pipe and the injector union connection were removed with a 14mm spanner and 13mm socket respectively. As soon as the union was removed the hole was plugged with a small section of kitchen towel pushed into the tapped hole. This simply prevents any bits getting into the open hole while working to extract the injector.

Rarely it is possible to clamp a pair of good mole grips to the injector solenoid fixing nut and rotate the injector ten or twenty degrees back and forth to loosen it in its bore, more often it takes a great deal more work!  Using a searching penetrant or diesel itself is a good aid to getting things moving. This twisting method can be successful, though what usually happens once you start to get going is that the fixing nut undoes slightly and puts a stop to using that method of extraction, as it simply rotates upon the head of the injector body.

What you have to do in this eventuality is grip the injector just below the solenoid nut and attempt to move the cast head part – rotationally back and forth. As the diesel supply union is completely removed, you will get the maximum chance of realising this important few degrees of movement, that will in time result in the total removal of the injector body.

If you have a 24mm open end spanner or its imperial equivalent this is your key tool. If your area of work is the rear three injectors there is a little technique that may work for you. If you lay a 19mm combination spanner along the top of the duct that carries the injector wiring, interlocking the open end into the rear intake manifold support bracket, this will provide a sturdy supporting surface on which to lay the ‘operating’ slightly slack fitting, 24mm spanner onto whilst moving it back and forth. As you will probably only be able to shift the injector a few degrees back and forth at first, it is important to keep the area well irrigated with penetrant. As your movements get more dynamic, begin to press the back of the operating spanner down onto the 19mm rider. Keep pushing as you rotate back and forth. This induces a small lifting force under the solenoid nut from the 24mm spanner and as you move it, it will in time begin to raise the injector out from its bore. If your injector is at the forward end of the engine you will have to locate the 19mm ‘rider’ spanner’s open end somewhere up-front to fully enable this method, but it is not impossible!

Mercedes CDI Diesel Injector

Eventually you will extract the injector – a feeling of achievement will appear as you take an inspection mirror and torch to peer into the blackness from where it came. If you were lucky then the copper washer/seal will have accompanied the injector out of the hole.  If not, a ‘rat-tail’ round file of suitable size, pushed into the hole will retrieve the seal without issue.

Now you can begin to inspect the seal itself, giving up many clues to the demise of its capability to hold pressure. Clean it with a rag and take a close look at its copper surfaces. If there are any scored lines, cuts or deep marking, this is the route the escaping combustion gasses have taken to ‘carbon-up’ your engine with ‘Black-Death’. Indeed any gas-cut passages in the sealing surfaces will have most certainly also cut into the aluminium injector seat and in severe cases damaged the steel injector face that mates with the copper seal.

I would recommend always at least cleaning the recessed seat of any removed injector with a special tool made for the job. This special tool is a flat face end-mill or reamer with the correct diameter sleeve to cut or reface the base surface with some precision. These tools are available from Laser for under £60 from most motor factors and are essential to DIY replacement and the successful re-sealing of injectors – experience has found in every case, if you don’t at the very least ‘lightly face’ and prepare the injector seat before reinstallation, you are not giving yourself the best chance of success, therefore I would get the proper tool for the job, period!

Escaping combustion gasses often cut the aluminium seat and this needs to be re-faced so that a perfectly gas tight seal can be maintained

One or two rotations with the seating tool will be sufficient to enable you see if the seat is damaged in any way, using your inspection mirror and light. If there are any black marks on the seat (rather like worms!) as the drawings below show, then continue to use the seating tool, checking and wiping aluminium shavings as you progress to remove material. Eventually the tool will re-face the damaged seat to show a clean, uninterrupted ring of aluminium. It is possible if you do not fully rotate the tool when using it, mistakenly rotating the tool left to right rotationally, may cause the finished surface to have ‘chatter’ marks on it. This is surface unevenness that must be removed and is only achieved by turning the tool lightly and continually in one direction, stopping movement only as you simultainiously relieve pressure from the cutter. Inspect and clean often, to obtain the best surface finish possible.

Improper use of the seating tool sometimes causes chattering on the surface of the seat. This needs to be smooth and not disrupted with tool marking

Now turn your attention to the face of the injector body that compresses against the copper seal. This must be free of any carbon build-up and ‘shiny clean’. You can take some fine emery paper and lightly work this surface until it is bright and continuously clean around its circumference. Now you are almost ready to reassemble!

The injector hold down bolts are a one-time-use, stretch to yield fastening, that must be new and unused on each replacement. Cut a short groove with a saw file to make a thread cleaner out of the old bolt and use this to freshen up the tapped hole for the clamp bolt. Use a thin screwdriver to clear the oily debris from the bottom of the hole as it often builds up here and can if not removed, be forcefully compressed into a plug, causing it to burst through into the cylinder head water jacket – take special care to clean this hole out!  If the thread is damaged in this deep tapped hole you have a number of repair options, these are covered briefly in this post.

Now you can use ceramic grease to coat the outside of the injector body (not the tip or any mating/sealing surfaces) place a new preferred Honda Accord Diesel Seal onto the injector tip and carefully lower it into the clean and prepared hole. Do be sure to have one final check with torch and mirror to make doubly sure there is no debris left on the sealing surface before final assembly. Once the injector is fully inserted, with the fuel connection pointing to the fuel rail, add the clamp and loose-fit the clamp bolt to hold things in place. Now refit the fuel union to the injector, removing the tissue plug that has prevented dirt getting inside, then refit the steel fuel line from the injector union to the fuel rail, finger tightening the union nuts. Now torque the clamp hold down bolt to 7Nm plus 90 degrees (MB Specs say 90 plus 90 degrees after 7Nm, but actually the yield has occurred after the first 90 degrees and clamping force reached, so I see little point in risking further stressing an otherwise ‘spindly’ and fragile fixing). You may now refit the fuel bleed off pipework, electrical connector and tighten off the steel fuel line unions. Rebuilding your engine is now a reversal of dismantling. (remember to remove the manifold intake plug of rags or paper before fitting the upper section!)

There are a few tips here that hopefully will help you achieve this sometimes daunting job, but with care, patience, the right tools and a little effort this can easily be done by a DIY mechanic.