XM Engines

Engine supports

Old and new mounts [Picture courtesy of Jens Bovbjerg]

There were the wrong type of engine supports fitted to early diesel XMs, supposedly up to Q1 of 1992). The replacement top ones are softer and taller, and have a different shape. In fact, the original ones made the engine sit at an angle (the gearbox end was higher by about 1/3 of an inch). Post-1993 microfiches show this replacement, pre-1993 ones do not. If you buy replacements, check that the salesman is checking the right microfiche or you may get the wrong supports: those for a 2.0 liter gasoline engine. The new supports made such a difference I though I had a different car!

The bottom supports of early engines may have been pressed in at a wrong angle. Citroën will try to sell you the whole aluminium support, not just the press-in rings vulcanised together with rubber. Try Peugeot instead: the same engine support parts appear in the 405 and 605.

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Changing adjusters

Some mechanics would tell you that the camshaft housing has to be removed (together with the camshaft and all that this implies, timing belt, etc.) to change the adjusters. This is not true, nothing more is needed than removing the camshaft cover and, naturally, knowing what to do.

It is difficult to figure out which one of the adjusters is dead. At most you can narrow it down to one cylinder. Take off the intake manifold extension part (black plastic or metal if fitted with EGR valve) by removing the hose from the intercooler and unscrewing three bolts in the back (two are under the plastic fuel hose holder, just pull them off), and unscrewing two smaller screws between the intake pipes of cylinders 1-2 and 3-4, close to the front edge of the head. If you run the engine at idle with the manifold extension off, you will hear a popping sound from the inlet of the cylinder whose adjuster fails. It is sometimes difficult to know which one it is, find a long plastic pipe approximately the diameter of the inlet on the head and put it onto each of the inlets in turn. The absence of the popping will be obvious when you put it over the inlet of a cylinder with the bad adjuster(s).

When you have localized the bad adjuster, stop the engine and open the camshaft cover. Wipe the gasket clean, it doesn't need to be replaced. You will see the rockers under the camshaft. Use something blunt that does not shed any particles (like a wooden spoon or a piece of plastic) to press on the side opposite the valve, the adjuster is under the rocker on that side. If you can press any of the adjusters down easily, they have either failed or will fail in the near future (the one-way ball valve in the adjuster normally makes it very difficult to press the adjuster down without applying a lot of force). Even if only one cylinder made the popping noise, other adjusters (not seldom all of them) can be already soft as well. The best way would be to change all of them as the rest will follow the bad one in due course but at least change all adjusters on the cylinder which was found generating the noise.

To replace an adjuster, turn the engine into a position where the inlet valves are open and the exhaust ones are closed (turning the engine is more difficult with an automatic gearbox, with a manual one you can simply put it into 5th gear and move the car a little bit). Press onto an exhaust valve until it moves down, push the rocker from the valve side towards the adjuster. Depending on the tools you have, you may even pull the rocker out by its wider part that goes over the adjuster. It will be a tricky operation, you might want to have a helper pushing down on the valve while you get them out grasping them on both sides of the rocker with your fingers (doing all this on a cool engine will be much more comfortable...).

Once you have removed the exhaust rockers, move the engine a little bit further until the inlet valves close and repeat the procedure for the inlet rockers. You will find that it is easier to knock the rockers off the adjusters by pushing them towards the center where the exhaust rocker were. Be careful not to lose the guiding parts on the top of the valve spring assemblies. As soon as all rockers are removed, the old adjusters can be pulled out easily.

Pour fresh oil into their hole and insert the new adjuster straight out of the package without wiping off the oil or squeezing them or anything. The rockers go back by carefully locating them (intake goes first), valve end first, until they sit on the valve, then pushing them over the adjuster. Move the engine back again until the exhaust valve cam is facing up, press on the valve and insert the rocker.

Close the rocker cover but before replacing the manifold extension, listen for the popping noise once more. It is normal to have some noise for the first seconds, it might even require to race the engine for a very short time to drive an air bubble out.

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Head gasket (diesel)

A new type of head gasket was introduced in 1993. The older one was a mica press with metal inserts, the new variant a steel-aluminum-steel sandwich construction. The old one failed for me at 130,000 km: part of the gasket lining burned out, leaking gases into the coolant as well as the adjacent cylinder. Such failure is not possible with the newer gasket.

If you need to replace it so you have to have the head off, don't forget to do a complete checkup at the same time, including valve adjusters and valve stem seals. With the camshaft housing removed, you can access the small filter in the oil supply of the camshaft. Take care to pull it out carefully and clean it. Also, clean the head and the housing thoroughly, there will be a lot of black gunk. You can now check the turbo, too: it's relatively easily accessible

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Timing advance solenoid (diesel)

This is a typical problem with CAV DPS/DPC fuel pumps. The fuel leaks along the edge of the solenoid housing (a round part with a huge nut on its housing, screwed into the side of the pump). Remove it by unscrewing it with the appropriate wrench, having unplugged the electrics first, of course. The leak develops where the back of the solenoid is joined with the rest of the body, and the replacement is very expensive (cca 160 Euros).

Alternatively, you can use fuel resistant, two-component epoxy resin to seal the leak by applying it where the back plate and body join. I used UHU endfest 300, this glue needs to be heated to achieve optimal curing, when heated it also becomes very watery which seals the crack well. The parts need to be cleaned thoroughly from anything greasy before the application of the glue, which is a challenge considering it's doused with diesel fuel.

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CAV troubles (diesel)

CAV fuel pumps give an endless amount of trouble. Problems with idle speed, speed oscillation, stalling are among these typical failures. In other cases, the engine might idle normally but it gets stuck at higher or lower idle revolutions when the accelerator is first pressed and released. Or it can get stuck at a certain speed over idle regardless of accelerator position.

The most usual causes are:

Incorrect idle speed adjustment

The engine revs up normally on accelerator command but takes long to rev down, or even gets temporairly stuck on a higher idle, then drops to normal. Idle oscillates slowly. Engine accelerates normally when accelerator is pressed, decelerates rapidly it is released and appears to stall shortly before picking up idle speed again, or even stalls completely, but restarts normally after cranking. Engine seems to run normally (possibly with slightly high idle) but cannot be turned off by rotating the manual shut-off lever on the pump.

Air leaking into fuel uptake

Engine starts but stalls after a few seconds and cannot be started easily (needs priming, low resistance to pressing the priming button indicates that there is air in the uptake).

Plugged up filter

Priming button on the filter is sucked in.

Water in the fuel

Occasional (but not constant) white smoke puffs from the exhaust when engine seems to stall temporarily or run roughly.

Fuel leaking out of certain parts of the pump

A leak from seal on the pump shaft can be difficult to check for, this is one of the things that should be checked when you replace the cambelt. A leak from the turbo pressure compensator assembly causes sluggish turbo or no turbo response, low turbo pressure until higher revolutions are reached. A leak from idle setting / cold idle / manual shut-off lever assembly shaft makes it difficult to set the (cold) idle speed. A leak from the electric run/stop valve can cause a failure to start, uneven idling or sudden stalls. A leak from the cold idle timing advance solenoid will result in rough idle, slightly higher noise and higher fuel consumption at normal operating temperature.

Stuck or worn auxilliary parts

The engine starts but stops after a short while, priming shows that there is fuel in the pump and under pressure (the button is out, it barely moves or doesn't move at all when it's pressed). The pump return one-way ball valve is stuck, mostly because of corrosion. It is ball and spring assembly located inside the hollow screw that holds the return pipe on top of the pump case. If there is no difference between cold and warm idle speeds: check the paraffine element on the engine. Check the electric contacts of the cold idle timing advance solenoid as well.

Worn out pump

If you have eliminated all other problems and the idle still gets stuck or the engine runs away, the pump produces subharmonic noise or clicking sounds, you might have a worn pump. The engine could run hot (even with the cooling system functioning perfectly), its power could be low even in spite of the injectors, cylinder compression and turbo working fine.

A combination of the mentioned symptoms is also possible, making diagnosing difficult. The complete troubleshooting procedure is as follows:

Give the pump an independent supply of clean fuel. The best way is to use a small canister filled up using the priming pump to pass the fuel through the filter. Connect the canister to the uptake and return outlets of the pump with transparent hoses. Position the canister higher than the pump in order to be able to syphon some fuel. Start the engine without pressing on the accelerator pedal (this might prove difficult until the air passes through, watch out for bubbles in the hoses). If the engine runs evenly without you touching the various control levers or even better, the idle lowers by itself as the engine temperature goes up (provided the paraffine element on the engine is working), start looking for an air leak into the uptake line.

It is best to get rid of any air leaks before proceeding any further as this will disturbe or even hinder the accurate setting of the idle speed. You can replace other parts of the tubing with transparent hoses so that you can look for bubbles in the fuel supply.

Loosen or disconnect the accelerator cable. If the engine stalls immediately, the idle adjust is misaligned (see below). Unscrew the screw that dictates the minimum position of the speed lever (this is the one the accelerator cable attaches to). If the idle speed drops or the engine stalls, the idle is misadjusted. Keep unscrewing the screw until it no longer touches the speed lever. Loosen the cold idling speed adjust cable going from the paraffine element on the engine to the pump.

The idle speed can be adjusted by the relative position of the manual stop and cold idle levers: these two small levers are mounted on a coaxial shaft just to the left of the main speed lever. There is a screw adjusting the maximum distance between these two. The larger the distance, the lower the idle speed. Thus, decrease the distance until you can start the engine normally and the idle speed is within the specification. If the car has air-conditioning fitted, remember to adjust the idle speed with the A/C on as mechanically controlled pumps (like the CAV ones) will always have the idle higher when the A/C is off. As the idle speed needs to be adjusted at normal engine temperature, you might need to readjust as the engine heats up.

Remove the speed lever damper if there is one. Move the speed lever slowly, the speed will not increase immediately. Keep the lever at the point where the engine speed just starts to increase. Then turn back the screw that determines the default position of the speed lever to obtain a 5 to 8 mm gap between this default and the position where the speed started to rise.

You should never increase the idle speed by adjusting the speed lever default position. The CAV pump has two different mechanisms for speed regulation, and without this initial free play, the two actions will overlap causing speed oscillations. Increasing this gap makes the engine respond more readily to the releasing of the accelerator pedal but slower to the pedal being pressed because of the added movement needed to go through the increased free play. Decreasing it has the opposite effect. Besides, increasing it past a certain limit will actually make the engine stall temporarily before the separate idling mechanism might take over, finally making it impossible to start the engine without pressing the pedal down. If the gap is too slow, the speed regulation mechanisms will contend resulting in the idle speed sticking, or oscillating. It may oscillate so largely that the engine dies on the bottom of the oscillation, unless you rev it up with the throttle.

Reattach the accelerator cable making sure that the adjustment clip allows the speed lever on the pump to return to the adjusted position. It may be necessary to check the attachments and the holders of the cable to reduce any unnecessary free play and unwanted oscillations on acceleration-deceleration as described above.

Reattach the cold idle speed cable but do not put any tension to it. Wait for the engine to cool down completely, preferably leaving it overnight, making the final adjustment early in the morning or on a generally cold day. Pulling on the cable decreases the angle between the manual turn off and idle speed levers on the pump, thereby rising the idle speed on a cold engine. The mechanism also has an electrical contact attached to it controlling the cold idle timing advance solenoid. Ideally, this should disengage before the idle speed drops to normal. The only way to adjust it is to extend or compress the spring under the contact. Make sure that the timing advance does not remain engaged unnecessarily.

Pull the two levers together until the desired idle speed is reached, then position the adjustable stop on the cable as close as you can to the levers. It will be difficult to get it right so you'll probably need several tries. If you find that the engine idles too high or for too long, you can carefully loosen the cable a bit. Idle speed and length of time involves a compromise, trial and error is the key.

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