Everyone loves a happy ending. Share your diagnostic success stories here.
- Posts: 65
- Joined: Sun Aug 27, 2017 8:00 am
Things seem a little quiet on the forum lately so I decided to post this one. A 2015 Suzuki Vitara 2.4 L Petrol. Problem a very very intermittent misfire on start up and sometimes a slightly extended crank with or without the misfire. Coils/plugs/injectors/ECU and ???? had been replaced. Febary 2021 I offered to scope the vehicle, a day and a half of various start scenarios no misfire. The dealer elects to use it as a courtesy car; call me when the problem is more predictable. October 2021 the vehicle is sold, early December it is returned for repair. This time I was able to capture the misfire, scoping #1 ignition injector and crank, not happy with the secondary pattern I reset the scope settings and in keeping with its bad habits it failed to misfire again. I went back over the misfire capture, engine control looked good, possibly signs of a lean misfire in the spark pattern? or mechanical, a propped valve? [doubt it]. Pico 7 Maths channels to the rescue!. Using crank and frequency maths channels I could clearly see the misfire on cylinder #1 with no rise on the graph and the graph compression dip prior to cylinder 1 ignition so no mechanical failure, Im going for fuel. I ask the dealer tech have you checked the fuel pressure. answer NO a pressure test was carried out and up to spec but no residual line pressure at key off. Under the right conditions the fuel drained back and with # 1 injector furthrest from the fuel inlet, vapour had to flush through before # 1 could fire. Its easy to be wise after the event and many of us have dealt with line pressure problems in the past, this one was probably not the norm, hence the title Never forget the basics. A new pump was fitted and the problem solved. I later learnt this had been a problem for 3 years
- Posts: 156
- Joined: Sat Oct 26, 2019 6:45 pm
Good catch !