Common Technical Problems

BMW swirl flap

One of most common diesel engine issues known in the BMW world is the failure of the swirl flaps in the inlet manifold.

The majority of inlet manifolds fitted between 2001 and 2007 on 4 and 6 cylinder engines had a bank of flaps which aid emission control at idle, when the engine speed increases these flaps will open fully until the engine returns to idle.

Due to the construction of the spindle and also the heavy build-up of carbon on the butterfly, it has been known for them to crack, snap off and be sucked into the combustion chamber which in the majority of cases leads to catastrophic engine failure.

There is no way of being able to tell which vehicle is going to suffer a swirl flap failure, so the safest measure is to have the swirl flaps removed and blanking plates fitted.

This has no effect on engine performance at all and gives you peace of mind that the engine is safe. 

Modification cost £168

Affected engines are M47tu and M57tu.

BMW N47 Timing chain and guide failure

A hot topic at the moment is the occasional engine failure of the N47 engine 2007 – 2008.

This problem seems to appear in higher mileage vehicles which may have been serviced with incorrect oils.

The issue is the degrading to the timing chain tensioner and guides which cause the chain to slap... If this chain slap/clatter is not addressed with urgency then the chain quickly wears down the upper and lower pulleys and, in the worst case scenario, the chain jumps sending the timing out which causes severe internal engine damage.

The repair to the timing chain alone is a costly repair as the engine is what would be called back to front where the timing is at the rear of the engine. To gain access the engine and gearbox need to be removed and dismantled accordingly. 

The average cost with Forza GB for the full timing chain, guides, tensioners and pulleys replacement is £1400.

We will shortly be offering an engine DeTox for this service.

BMW Z4 convertible hood motor failure

This is a common fault but there's a simple procedure which could prevent it from happening.

Basically the hydraulic motor is sat in the nearside under the convertible hood. It lives inside a flask which is foam-lined and this flask lives in the cavity where rainwater runoff travels.

Under this flask is a drain tube which is approximately 6mm across and is not accessible. Over time natural dirt, silt and debris blocks off this outlet. The cavity fills up and then fills up the flask that holds the hydraulic motor. The motor then burns out.

If it fails then a replacement can be fitted and a few modifications carried out to prevent a further failure.

If it hasn't failed then on every third oil change we recommend the nearside wheel arch liner is removed and the drain tube is cleared out.

BMW X3 2.0D M47 2006 - 2008

Fault code 3ff0

This code comes with the symptoms of lack of power, hunting, sporadic misfires etc.

The most common findings after diagnosis is a heavy build-up of carbon on the EGR valve. Then once the inlet manifold is removed a heavy build-up of carbon in the inlet ports too.

The only true repair here is to carry out a full decoke which involves removing the cylinder head, removing valves and cleaning out all affected areas.

To help prevent this, we recommend a fuel tank additive which will help keep the major components clean.

We will shortly be offering an engine DeTox service for this issue.

BMW MINI Cooper S power loss at 4000rpm + FC 1688

The cause of this is the throttle bypass valve staying open after throttle on.

There is a spring which forces the butterfly shut when required – this spring is brittle and has a tendency to fracture.

The easiest repair here is to replace the bypass valve.

BMW 1 & 3 Series

Sporadic DSC brake interaction and tyre pressure warning light comes on. No faults logged in DSC.

This fault is normally due to corrosion behind the rear reluctor rings which are fitted to the drive shafts outer CV joint, the ring then distorts and makes contact with the wheel speed sensor sending a false signal to DSC.

The repair at BMW is to replace the driveshafts and sensors complete and on occasion the wheel bearings also.

At Forza we remove the driveshafts and replace the reluctor rings rather than the whole driveshaft which massively reduces the overal cost of the repair.

The current cost for this service is £447 (replace both nearside and offside reluctor rings and wheel speed sensors).

BMW M57n Cracked Exhuast Manifold

A really common issue which results from a poorly constructed manifold. The manifold suffers from hairline cracks which allows exhaust gases to escape into the engine bay and into the air intake for the cabin. These gases are Toxic and can cause harm to the occupance!

It has also been known that fragments from the inside of the manifold fall off and damage the turbo and in extreme cases be drawn into the EGR cycle and taken back into the engine.

We replace the manifold for a cast version which will outlast the vehicle.

The current cost for this service is £400 (manifold and new gaskets)


Mercedes-Benz M271 engine sprocket and chain wear

We recommend that the chain and sprockets are checked at every major service as excessive wear can lead to premature engine failure.

This issue is due to a combination of faults within the timing chain section. The camshaft adjuster sprocket teeth wear out due to metal fatigue and is caused by the upper plastic chain guide breaking up and falling off, the chain is then allowed to run on an aluminium bridge. The chain grinds away at the bridge which draws swarf into it and onto the sprockets & guides causing accelerated wear.

The repair depends on condition of the engine but if caught before the timing slips then the sprockets can be replaced without the need to buy the complete Camshaft adjuster from Mercedes. The timing chain, guides and oil and filter are also replaced.

MINI Convertible R52

Sunroof opening failure.

Extremly common for the R52, symptoms are normally a large cracking noise from either side followed by non movement of one side.

The fault occurs when the cable mechanism snags in the side runners, either the cable snaps off or the guide cracks.

To make an effective repair the cable mechanism and modified guides need to be replaced. It takes approximately 2-3 hours to complete the job, the parts are only availible from MINI and are cira £500.

Porsche AOS valve failure

Excessive oil burn on start up and when driving!

This often happens suddenly and if it does please stop driving immediately as it can cause extreme wear/damage to the engine.

The AOS (Air/Oil separator)valve is a plastic housing with a rubber diaphram inside, the diaphram splits which then allows the vacuum of the induction manifold to act directly to the inside of the engine causing the oil to be sucked out and into the induction cycle. We have had cases where the engine has been starved of oil damaging the cylinders (Number 1).

we recommend replacement at about 80,000 miles however this is just a guide.

Cost for replacement varies greatly depending of model, the boxster 996 for instance can be done in situe where as the Carrera 997 needs to have the engine removed to replace the AOS valve.

Please contact us on 01291 624563 for an estimate for this service.

Porsche IMS bearing replacement 986/996 some early 997's

The IMS (intermediate shaft) bearings are prone to failure. Should the IMS bearing fail it WILL lead to catastrophic engine failure as the engine timing chains and the oil pump are linked directly to the shaft.

The cause from what we understand is the seal for the bearing fails/shrinks which allows engine oil to seep into the bearing flushing out the bearings grease, this then causes premature wear of the bearing.

It can be possible to spot potential IMS failure by checking the oil filter for metalic debris during an oil change or oil seepping out from between the engine and gearbox bell housing, if this is the case then immediate actin is needed.

If the clutch is being replaced at any point then we highly recommend the IMS is replaced at the same time as it save onthe labour charge.

There are various options for replacement from an original Porsche IMS to uprated versions.

Replacement costs from £995

Please contact us on 01291 624563 for an estimate for this service.


DPF (diesel particulate filter) All diesel vehicles

An increasing issue for many latest generation diesel vehicles are blocked DPF's. There are many reasons for them becoming blocked, whether its reached its end of life cycle to premature blockage due to adverse driving style (many short journeys) or even poor fuel quality.

Assuming the engine is peforming correctly and there are no faults logged within the engine management then the system should, when required, carry out a regeneration which will expel excessive soot deposits within the DPF, but this doesn't always work. A common cause for regeneration to not take place is the glow plugs failing.

Usually the repair for a blocked DPF is to rectify any faults logged in the engine management that may inhibit a regeneration (glow plugs etc) and replace the DPF or remove it and send away for cleaning.

We now have the equipment to offer an in house DPF cleaning service where the soot/ash is disolved and removed from the DPF returning it back to its original state.


BMW diesel Turbo failure due to carbonisation within the engine oil galleries

Again, another common issue with modern diesel engines with extended oil services is a build up of carbon in the induction cycle and more alarmingly within the engine oil galleries. The best analogy for this is carbon build up in oil galleries is the same scenario as cholesterol (LDL) build up in your arteries, too much and it has severe consiquences on your engines health and excessive carbonisation in the induction cycle means the engine cant breath correctly and receive the oxygen it requires, a bit like Asthma restricting a wind pipe!

One of the major components which frequently fails due to carbon build up is the turbo, the high pressure oil pipe that feeds the turbo bearings becomes restricted and oil flow slows or stops staving the bearings of lubrication. The bearings overheat and the turbo impellor shaft then distorts or shears off.

To help prevent this carbon we are coming up with a series solution which will recommend happens at every 3rd oil change (circa 60,000miles).

During the oil change a machine will be attached to the engine, this machine will break down and flush out all particals including carbon & varnish. Not only does this help protect the life of the engine and its componenets but it improves the overal engine performance and MPG.

In addition to this we also have equipment to decarbonise the industion system, including the inlet manifold, EGR (exhaust gas recerculation). By removing this carbon it will allow the turbo to work at normal operating speeds, improve the drivalbilty of the vehicle and MPG as well as help prolong the life of the DPF.

We will be offering a full vehicle Detox service with more information to follow.....


BMW E46 M3 and Z4M rear exhaust flanges corroded or cracked

Rear exhaust flanges corroded, cracked or partially missing.

The flanges that hold the rear ehaust box to the centre pipes are of a poor casting and the metal suffers with heavy corrosion leading to them cracking and becoming insecure. Due to the design of the flanges BMW's recommendation is to replace the rear exhaust box and/or the centre section which is extremely expensive. It is also known to be an MOT failure due to exhaust insecurity.

We now carry specially designed flanges which are a direct replacement.

The replacement of the flanges is £250.00 (inclusive of parts, labour and VAT)


Audi Q7, A8, Allroad C5, Porsche Cayenne, BMW X5 Wabco Air suspension compressor failure

Symptons for this fault are;

Noisy compressor

Slow to reach requested height

Failure to pump at all

Air suspension failure warning light on.

The cause of this fault is generally down to the poor quality seals that are used inside the compressor. Once the seals begin to break down then the compressor loses its efficiency and eventually the ability to compress the air.

Rather than replace the compressor we carry out a repair that involves stipping the compressor down and replacing the seals inside.

The cost for this service is £120

Prices shown are including VAT

Forza GB – Service beyond expectation