Mazda Sedan Range

A car like this shouldn’t frighten too many mechanics, largely because this is a fairly simple machine using well-understood technologies. In a situation like this one, most workshops will go back to first principles. That is: Air, fuel and spark.

On the surface, it sounds like a fuelling problem that is causing the engine to run out of fuel when it needs it most (when accelerating). So a check of the fuel filters, the fuel pump delivery pressure and volume and the injectors would be a good place to start. However, stumbling under load can also be caused by poor ignition, so the spark plugs, leads and coil(s) and charging system should also be checked out. Don’t forget things like a dirty air filter which also cause a case of the stumbles.

If all that checks out, then you need to start looking for a dud sensor somewhere in the engine bay. An electronic scan is a must for any electronically-injected car.

Most mechanics will do a complete check up and tune of the engine as part of tracking this problem and it’s a good start, because a new set of spark plugs and plug leads might just fix this problem. But that won’t always be the case. As such, you could be looking at a dud sensor somewhere in the engine bay that is telling the on-board computer to shut things down or, at least, not providing the computer with enough information to keep it all running. For this reason, an electronic scan of the vehicle should also be carried out at the same time to see what fault codes are cropping up.

A prime suspect for this behaviour would be what’s called the engine’s stepper motor which is a small electric motor that controls the throttle body and, therefore, the car’s idle speed. If this motor is maladjusted or faulty, it could cause the engine to either idle roughly, too slowly, or stall altogether. But have the scan done before rushing out to spend money on parts that may or may not be the problem.

It’s a bit silly, isn’t it? There’s absolutely no reason for a speedo in an Australian delivered car to read to 260km/h, particularly in a car that would never manage to gain that much velocity without the help of a mine-shaft. There’s no ADR requirement for it, either, so it’s probably a hang-over from other markets where average freeway speeds are much higher than they are here. In Germany, for instance, where there are still unrestricted sections of autobahn, the 200-plus-km/h speedo makes more sense.

You’re probably right when you suggest this is all a one-size-fits-all approach by Mazda (and many other car-makers) who can save a few dollars by making only one speedo calibration and fitting it to cars for every market. More recently, a lot of cars have both a conventional and a digital speedometer fitted. Many owners have come to rely on the latter for clarity. My preference is for an analogue (needle) speedometer that has 100 or 110km/h at the 12-o’clock position on the dial.