Great Wall Reviews

In order to find the remedy, you first need to know the cause. On this vehicle, the P0300 code indicates a misfire in one or more of the cylinders of the engine. In the majority of cases, this can be traced to a faulty coil, high-tension lead, spark plug, computer or even the fuel system. The warning shows that one of the cylinders is not firing as cleanly as it should be, so those are the basic thigs to start with. The problem could be as simple as moisture inside one of the coils or its fittings, or even a simple dodgy spark plug. If that’s the case, replace all of them, rather than just the one that’s faulty, as the rest are also likely to be getting towards the end of their life.

There are plenty of reasons why a diesel won’t start in the morning. This can often be traced back to a problem with the fuel system or the glow-plugs which are needed to warm the combustion chambers before the diesel will ignite.

As for the noise, it pays to remember that diesel engines are inherently noisy, but if you’ve owned the car for a while and are familiar with its normal level of racket, then any new or louder noises signal a problem. If, indeed, the new noises are connected to the engine’s refusal to start easily, you might be looking at an engine with worn out internals. At that point, it’s time to recondition or replace the original engine.

But before you do any of that, have a diesel specialist look at and listen to your engine running, and you might find the problem is a simple one after all.

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.