A Volkswagen Crafter was purchased privately by a garage. On delivery, the driver did not notice any issues before accepting the vehicle. Unfortunately, the next day it began to smoke white/grey from the exhaust. But as there was no warranty, and the seller did not respond to any calls, the new owner was left to sort out the issue.

To top it off, the Crafter was bought as a service van for the workshop.

They scanned the engine ECU for any fault codes, but there were none logged. As this was a Euro 6 model with Selective Catalytic Reduction (SCR) fitted, they suspected the AdBlue system was the root cause of the white emissions from the exhaust, but there were no traces of crystallized AdBlue present in the tail pipe. So this was not the cause of the smoke.

Thinking that the fuel might be contaminated, they drained and replaced the diesel fuel. After an extended road test, the issue persisted.

So the helpline was contacted to assist diagnosing the issue.

We asked for a data scan with the engine at operating temperature, and on analysing the data, we noticed something very obviously wrong with the injector smooth running figures.

Smooth Running
Here’s a breakdown of what Smooth Running means, how it works and why it is important.

Injectors, even when new, don’t always deliver fuel perfectly evenly. The ECU uses “injector correction” or “minimum deviation quantity” to account for these differences.

Balanced Fuel Delivery
By adjusting the fuel delivery for each cylinder, the ECU aims to ensure each cylinder receives the correct amount of fuel, leading to a smoother, more efficient and quieter engine.

On this vehicle, the values did not balance. And the cylinder torque values showed an issue with cylinder 2. It was producing a very low power output.

In internal combustion engines, each cylinder contributes to the overall torque output, with the torque produced during the power stroke of each cylinder being transferred to the crankshaft via the
piston and connecting rod. A lower torque output on one cylinder will create a situation where the engine will not run smoothly.

Here’s a more detailed explanation:

• Torque Production: Engine torque is generated by the pressure exerted by the combustion gases on the piston during the power stroke.
• Cylinder Contribution: Each cylinder contributes to the total torque output of the engine.
• Crankshaft Rotation: The torque generated by each cylinder is transmitted to the crankshaft, causing it to rotate.
• Torque Measurement: Torque is measured in units like pound-feet (lb-ft) or newton-meters (Nm).

    Cylinder number 2 was producing only 81 Nm of torque. The other three cylinders were producing 580 Nm of torque.

We suspected a compression issue with cylinder number 2, and as the injector was trying to overcome this deficiency by injecting more fuel, and the poor combustion pressure in that cylinder was creating the issue with unburnt fuel.

We needed to confirm the diagnosis, so we employed the Pico diagnostic software. This is a relatively simple test that requires the engine to be prevented from starting and analysing the battery voltage spikes. We unplugged all injectors and proceeded with the test. The Pico software will then confirm a cylinder compression issue.

The Pico software will analyse the battery voltage spikes over several engine cycles. This took 13 cycles @305 rpm to calculate the readings. Repeating the test several times gave the same results showing one cylinder low on compression.

Additionally, a traditional compression test now confirmed that cylinder 2 was the issue.

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