Technical Bulletin Fiat Bravo Injectors
II thought it would be of interest to our regular visitors to discuss some of the common problems with Fiat Bravo injectors. There is no doubt in my mind that having produced reliable injectors for many years the manufacturers have lost the plot a little.
Looking at the possible symptoms first, total injector failure will of course be fairly straightforward. In cases of severe misfire, the affected cylinders will have clean or normal plug condition, whilst the unaffected cylinders would however appear to have richer than normal plugs, due to the Lambda sensor attempting to correct the fuelling caused by excess oxygen content. A DTC underlining an injector error should be expected but is by no means guaranteed.
Partial failure presents some interesting symptoms; slight misfire, hesitation or mot failure due to the excess oxygen content, pushing the tail pipe Lambda valve over 1.03.
Testing is fairly straight forward, with the right tools. Access to the injector loom is simple; a 5-pin socket at the near side inlet manifold allows a number of options. Using an oscilloscope with an inductive current clamp, attach one channel, the trigger, to each injector circuit in turn, with the current clamp on the common power supply. Observe the waveforms when cranking or running the vehicle.
Total failure of the injector will produce an open circuit or short circuit condition. The triggering will display pulse and no power line, i.e. the voltage display will be at 0 Volts. The second channel will display 0 amps current if the injector is open circuit, with the possibility of excess current if a short circuit is present.
In my experience I have never seen a dead short or damaged ECM due to the excess current flow. I have however seen many injectors with a partial short causing excessive current whilst still delivering fuel to the engine. The other reliable symptoms are shown in the induced voltage spike at the point of injector closure; this would normally be around 64v with Bosch and IAW systems, Hitachi systems produce a spike of 90v. Note the normal current flow of 1 amp is increased to 2 amps with corresponding dropping voltage on our faulty sample.
The Fluke oscilloscope set up is straightforward; channel A triggering on pulse width greater than 1.08 m/s with a voltage threshold set to approx. 5-10v. This totally eliminates miss-triggering due to noise spikes when using a full band width of 100 MHz. Channel B set 1-1 attenuation with a conversion factor of 1 amp per 100 mv. The second option is Resistance measurement, and although not as informative, it is however reliable and accurate. Injector resistance at ambient temperature should be extacly 14.5 W. For the mathematically minded the following simple formula should help:
Hence with normal regulated voltage of around 14-15 volts a current of 1 amp is normal. When cranking, say with a voltage drop to 10 volts, expect a current flow of 0.7 amps.
Waveform 1
Waveform 2
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