Ignition fault

16 April 2015  

By Andy Crook

Diagnostics is often as much about proving what isn’t wrong, as proving what is. A robust, tried and tested routine is essential for efficient diagnostics. The symptoms and the lack of fault codes made me think mechanical rather than electrical issues were the problem and this was discussed with the customer.

The smoke test proved that the intake system was in good, working order. However, while the engine was warming up for the compression test, it was noticeable that it wasn’t firing on all six cylinders. So while I waited for it to reach normal operating temperature, I checked for ignition outputs at the coils.

There was no output on coil six. Knowing the coils had been changed meant that the next step would be checking the input/output at the ignition amplifier. Five inputs looked like Figure 1, number six looked like Figure 2.

Now we had hard evidence, we had to test further back – that meant at the ECU. This is in the passenger footwell and upon removing the covers I was greeted with the sight of multiple repairs, poor electrical connections and water damage, see Figure 3.

The signal from the ECU was identical to the signal at the amplifier. A volt drop test proved the condition of the wiring between the ECU and the amplifier, therefore the ECU was the cause.

andy@gotboost.co.uk

Figure 1

Figure 2

Figure 3

Figure 4