Renault Twingo II 1.2l turbo misfire

I was called in to look at this vehicle, because it was suffering from poor performance due to misfires on cylinders 1 and 4.
The garage had identified dtc’s for cylinder misfires on 1 and 4 and replaced the ignition coil pack.

This engine uses a wasted spark coil pack, which means 1 channel serves cylinders 1 and 4 and the other channel serves 2 and 3.
By replacing the coil they seemed to fix the misfire on cylinder 4 but not cylinder 1.  This confused them, as they had already swapped the spark plugs around, along with the HT leads to no effect. So they returned the new coil and called me in.

I carried out a quick scope analysis of the ignition and found a definite coil pack fault. (Sorry, no saved waveform sample).  I had the coil pack replaced again and confirmed that the performance was corrected on cylinder 4.  This just left me with the misfire on number 1 cylinder.  So I then carried out a full set of compression tests and verified all cylinders as good.
This left the challenge of the fuel system, as once again I faced no fuel pressure test port. I did, however, manage to adapt a coupling to the line feed and analyse the fuel pressure and injector performance, using my WPS500.  This test showed good fuel pressure, but thanks to the power of Picoscope, a closer look at the injector profiles revealed that injector no.1 was over-delivering.  The waveform image below illustrates this perfectly.

twingo fuel injectors
Fuel injector delivery analysis, showing excessive fuel pressure drop from injector No.1

In fact, on closer examination there is a sign of potential injector no.3 failure in a similar way, as can be seen in the above image. However, the one injector was replaced and the vehicle was fine.

As usual for me, I don’t have an after repair sample to show, but you can see, from my other case files, what a good set of injectors should look like.

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