How to Diagnose 1KD Injectors – Dont risk engine damage

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The Common Rail injectors fitted to 1KD engines are fairly problematic and can cause significant engine damage if left unattended. Most common failure mode is known as ‘cold knock’ which essentially sounds like there is a major fault with a bottom end bearing – only whilst cold.

Fault is caused by the spindle in the centre of the injector seizing / sticking when cold, which causes an excess of fuel to be inputted into the cylinder. Its for this reason why people usually sight ‘individual injector correction’ for how to diagnose these injectors. Obviously, when an injector starts to dump fuel, the ECU will start to deduct the fuel, and hence this was clearly evident.

The next most common failure mode is the simple wear out of the injectors due to the high pressure erosion.  This is most evident from black smoke and a drop off in bottom end power (off idle – although the gradual decline might mean the owner does not notice). As stated, this is caused by the high pressure essentially wearing out the internal components. This normally happens around 250,000kms, which I believe to be the ‘useful’ lifespan of these injectors.

Individual Cylinder Corrections > how they work:

There is a lot of importance placed on these individual cylinder corrections for when looking at the condition of the injectors. Whilst these figures are an awesome tool for looking at the injectors, they are not the entire story.

These corrections are derived by looking at the rotational speed of the engine at idle. Essentially, the idea of the system is to adjust the theoretical amount of fuel the ECU thinks its injecting to even out the idle speed and have a nice even idle. Normally, most of the variance from this idle is in fact caused by the injectors, but also things like individual cylinder compression, blocked intake manifolds (which will effect 3+4 worse than 1+2) suction control valves and fuel pumps will also all have an impact.

Therefore, simply looking at this number alone can lead to mis-diagnosis.

This only has an effect at Idle.  The ECU has no means to ‘learn’ fuel volume values under load and therefore (despite popular belief) the ECU cannot learn fuel values (although it will learn timing). To put it logically, if the ECU could learn, it would know that one cylinder is dumping fuel in the case of cold knock and correct it quickly, but it doesn’t….


By far and away, the most common causes of failure is the cold knock, however to properly diagnose it, it’s only logical that we view the car when cold.

Essentially, we like all of the individual injector corrections to be within +/-2.5mm3 / stroke cold or hot. We normally find that beyond this, cold knock issues will be evident. Obviously the higher the number, the worse the symptoms will be.

In terms of the next common failure mode (standard wear and erosion), we diagnose this when hot.  Essentially, we these clearances wear, the internal fuel leakages are higher (coupled with a less effective admission of fuel into the cylinder) which means more fuel comes out the leak off, rather than being put into the cylinder. Therefore, the amount of fuel that the ECU thinks its injecting will be massively increased.

New / Blueprinted injectors will have an injected volume of 4.5-6.2mm3 / stroke to idle when vehicle is up to temperature with no accessories on. We’ve seen these as bad as 13-14mm3 / stroke (i.e. there was that much wear, the ECU needed to hold the injector open 3 times longer just to get the same amount of fuel).  We normally recommend that anything over 9.00mm3 / stroke would require changing, especially if you require the seals to be changed.

If you’re one of the more ‘handy’ blokes, you’ll be easily able to take these notes yourself and be able to self diagnose more regularly to ensure your not putting your engine at risk. To take these numbers, you’ll need a Techstream or suitable Scan Tool

Lastly, Don’t stress. I’ve only heard of 2 engines letting go with NO Warning or genuine reasons (we’ve sold well over 12,000 injectors now). Most that have, have had cold knock, white smoke, chips or fuel contamination. With support of BDG and some general vigilance like this, stop stressing,  your 1KD will be fine!