Hi all, this is my first go at a case study so here goes:
Vauxhall Zafira 2002 reg 1.8 petrol z18xe engine code, a friend of mine who runs his own workshop had this in originally for a oil leak, leak from the crank sensor so this was replaced(something i did not know about until a while later into the diagnosis), after a few weeks the vehicle was back with a engine mil on/flashing and misfiring. he does not have a lot of diagnostic tools as he mainly works on older vehicles (he was tinkering on a morris 1000 when i was working on this zafira) so i went over with my scantool and my pico scope and wps500 pressure sensor.
codes were p0302 cylinder 2 misfire and p0303 cylinder 3 misfire (amongst a lot of other intermittent codes) so cleared, revved the vehicle and it dropped to two cylinders at idle, codes were p0301 cylinder 1 misfire and cylinder 4 misfire, this was a tad bizarre and after scoping the injectors the ecu was shutting down cyl 2-3 injectors sometimes and then shutting cyl 1-4 injectors another time.
inputs were next on my list to test, i scoped the crank and cam sensor and noticed the crank amplitude looked weak, see zoomed in waveform below:
i did notice the crank sensor looks rather fresh so quizzed friend, he told me the story about the leak and that the customer bought the sensor off the internet, i fitted the old sensor with the seal off the new sensor so it did not leak. engine revved clean as a cats backside and idled sweet, i took a waveform of a good crank amplitude see below:
job done, few days later car was back with a lack of power so i was called back, no misfire but engine struggled to rev passed 3000 rpm, a vacuum reading showed 21" of mercury at idle but did drop after a few minutes to 18", still ok but i was suspecting a blocked cat as this has had a few days of dealing with a misfire. usually i remove the pre cat lambda to see if there is a pressure release but this one was seized solid. the wps500 pressure sensor was sitting there so using some secondary extension leads i analysed cylinder 1 compression waveform to see any abnormalities.
everything looked ok at idle but when you snapped the throttle the exhaust back pressure topped at 46psi, slightly excessive in my opinion, see waveform below:
i temporarily decatted the vehicle and full power resumed and it revved to the redline.
at this point it was getting late so unfortunately a good waveform is not available which is a shame but i hope this may come of some use.
the moral of the story(in my opinion) is to fit high quality sensors and actuators, if a good quality crank sensor was fitted then there would have been no issue.
this just proves the power of the pico and the awesome power of the wps500, i think im scratching the surface with what the wps can do, its going to be a good learning curve.