Great Wall Reviews

That’s an odd one, to be sure. I’ve never heard of an engine that used different sized spark plugs in different cylinders, so you’d have to assume it’s the result of somebody only doing half a job when the car was serviced.

There’s at least one possible explanation for this, though. You might find that one of the spark plugs is difficult to reach or access. In that case, a lot of amateur mechanics will leave that one plug and replace the others with new plugs that have a different sized insulator (the white, ceramic bit you can see poking out of the cylinder head). It’s always best practice to replace spark plugs as a complete set, but lazy mechanics will cut sometimes corners.

There’s also a very slim chance that a previous mechanic has used a different sized spark plug during a routine replacement because they didn’t have four new ones that matched.

Spark plug size is critical in many respects. As well as having the correct threaded section to fit the cylinder head, a spark plug’s internal dimensions are crucial to ensure it doesn’t poke too far into the combustion chamber and make contact with the piston. It also needs to be located correctly in the combustion chamber to ensure proper ignition of the fuel.

You’d be surprised at how much load an air-conditioner places on an engine, especially when it’s idling and not making much power or torque. It can certainly be enough to make the engine labour and drop revs, forcing it down to a speed where it can no longer idle smoothly; almost as if it’s trying to stall.

Carmakers get around this by programming an idle-up function into the car’s computer. This detects that the air-con has been switched on and will then tell the engine to idle a little faster to keep everything running smoothly. If this idle-up function is not working, you can get the precise symptoms you’ve described. However, if this is the cause then make it GWM’s problem to put right, as it amounts to a fault and should be covered by the new-car warranty.

The failure to load the sensors is probably a centralised computer problem, since it’s more than one sensor (it would be an amazing coincidence if three sensors died at once). Either the Bluetooth connection is iffy, or there’s a software problem with reading what the sensors are saying.

I’m unsure how Great Wall can call the tyre-pressure sensor monitoring system a consumable. Yes, things like brake pads, tyres and batteries are considered consumables and not covered by a new-car warranty, but the tyre pressure monitoring system should last the life of the vehicle and is an important safety feature. I’d be ignoring the dealer and talking directly to GWM’s Australian customer service department and asking the tough questions. Australian consumer law is pretty clear on matter such as this one.