BMW 320SI – Diagnostic Session

Time and Time again we see vehicles that have been to garages that done have a clue, This E90 is no normal 320, it’s a limited-run homologation special of BMW’s world touring car with just a mere 2600 made available worldwide.

The 320SI is based on the 320i M Sport, the suspension, gearbox, bodywork and interior are all carried over unchanged. The areas that have been tweaked include the wheels (unique 18s), brake discs (now 300mm all round), and most significantly the engine, which is hand-built specifically for the 320si with more power and a very different character from the regular version. It may be stretching the point to call this a latter-day four-cylinder M3, but it’s well on the way.

The 320si engine is no mildly tweaked version of BMW’s regular 148bhp 1995cc unit. It has been engineered to rev higher; the bore is up by 1mm to 85mm and the stroke down by 2mm, to 88mm, while the induction and exhaust valves are all bigger, too. The compression ratio is up from 10.5:1 to 11.0:1, cylinder liners are aluminium alloy rather than cast iron, and there’s no Valvetronic induction system. The cylinder head is cast alongside BMW’s F1 engines.

But it takes lifting the bonnet to unearth the most exquisite part of all: a carbonfibre cam cover. The fact that this saves 10kg and lowers the centre of gravity is valuable on the race car, and largely irrelevant on the road car. What matters here is that it looks as cool as hell.

The upshot of the changes is that the 320si’s engine develops 171bhp at 7000rpm. The 0-62mph time falls from 9.8 to 8.1sec and the top speed is up by 6mph to 140mph.

This particular 320SI is in poor shape engine wise. Oil hasn’t been changed in sometime and is 9000 miles overdue. Unfortunately, this has resulted in the engine burning oil and damaging the cat.
As with so many cars, the vehicle has been to what many might call a cowboy garage where the customer was advised to change all four O2 sensors. If that advice had been followed the customer would have spent money replacing unnecessary components and the fault would remain unfixed.
All too often garages with generic equipment and a lack of understanding think they have skills they don’t have and throw parts at a car.

If the car had undergone regular oil changes (we think customers should exceed what BMW recommends and change oil between 6000 and 10000 miles) this problem would have been avoided, the customer wouldn’t have a damaged cat and damaged engine.

Lack of oil changes in a BMW typically causes:-
VANOS Faults (we do one of these a week)
Timing Chain Stretching
CAT failures
And in the worst cases Compression Issues.

The cars CAT really need changing. It’s a special double manifold design that isn’t stocked in the UK by the dealer and is special order from Germany.
Whilst two cats isn’t uncommon on a BMW certainly on a 6 or 8 cylinder engine however it is uncommon on a 4 cylinder BMW.
The part supplied by BMW isn’t even new, its remanufactured and is supplied on an exchange basis.

Whilst just changing the cats might resolve the issue in the short term, because of the engines condition it’s probably just going to get ruined by the oil and smoke being emitted by the engine.
Trying an engine flush might help the oil issue, but what if there are bigger issues?

Our advice is simple. Don’t let a MOT garage that doesn’t have any real BMW/MINI knowledge work on your car for anything other than an MOT or tyre change. We certainly don’t think the other garage was trying to cheat the customer, but rather just lacked the experience, skills and tools to accurately diagnose the car; especially with this vehicle with its limited-edition engine. In the long run what seems like a “cheap” code scan will result in unnecessary work that doesn’t resolve the problem.

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