Petrol Injection Systems

The wafe form below shows the output of a really cheap MAF sensor fitted to a Vauxhall Corsa 1.0L, which had been suffering from poor performance.
The original MAF had been replaced as the most likely cause of the fault.
When the vehicle's performance was no better, in fact possibly worse, the mechanic started looking elsewhere for the cause. He replaced many other components and spent a lot of time looking and failing to get to the result.
I was called in to look at it.
The sample below is what I saw:

The following sample is of a good MAF fitted to the same vehicle, which did cure the fault.
Spend a little more on the part and less on the job.

The wave form below shows both the front and rear oxygen sensors working correctly at 2000 rpm, no load. The sample is one of a 307 EW10 engine.
The Red wave is the front sensor, the Green is the rear sensor.

The following wave forms illustrate both the voltage signal and the current trace for an injector. This was sampled from an EW10 engine.
The current trace, (Blue wave), shows the, characteristic, step in the current, which is a result of the injector pintle lifting off it's seat.

The image below is that of a 'Trendplot' recording from the scopemeter. The fuel injector and pump supply, drops out intermittently, causing vehicle to stall. This is due to the 'double' relay failing. This fault did not flag a fault in the engine ECU.


The fuel injector signal below, taken from a vehicle with an injector misfire, illustrates the lack of induced peak voltage on the rising edge. This is due the solenoid windings being open circuit.


The wave form below shows the relationship between the throttle pedal sensor and the motorised throttle response. Taken from a TU5jp4. The blue wave is the throttle pedal.


The wave form below is a conventional view of the manifold absolute pressure sensor (MAP) taken from a TU3 engine. It shows the signal from idle to wide open throttle (WOT) and back to idle. This is a good signal.

TU3 MAP sensor

The wave form shown below is that of a Air Mass meter, taken from an Audi A4. The signal shows the engine at idle to wide open throttle, (WOT), although not for very long. The signal doesn't reach it's maximum but does indicate a good reaction.

Audi A4 Air Mass meter

Last Reviewed: 14 October 2017Copyright © 2004...2017 Mark Stammers