AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |
Back to Blog
Looking at the scope readings (see Figs 3 and 4) I was able to identify that our vehicle was suffering with two driver stage problems and the cause of this was the worst case scenario – a leaky driver in the PCM. If this occurs it will drastically reduce the energy induced into the primary winding. When examining events like current interruption its likely you will need to choose a time base range in micro seconds – that’s over 1 millionth of a second!The interruption should be prompt and clean with minimal, if any, rounding or glitches as the current flow reduces. Re-checking the peak current flow confirmed a healthy 8A peak flow on all 4 primary circuits, however when examining the process of interruption a different situation became obvious. The process of charging and discharging a coil is referred to as ‘inductance’ and the primary functionality includes peak current flow and speed of interruption. There was no way that this could’ve been due to the coil or the plug so it had to be down to the low tension circuit, however I’d already checked the peak current flow! Back to basics it was then. A discernible lack of energy was noticeable on cylinder no. It was at this point and, completely by chance, that I noted a discrepancy in the ignition energy delivered to the spark plug, by introducing a gap between the lead and plug. Somewhat puzzled I decided to remove the coil module and attach the ht extension leads that come with the Pico ‘Advanced Kit’, before attaching the ht inductive lead directly to the secondary ht circuit. Drivability was excellent over some 4.5 miles of mixed conditions, yet worryingly when I embarked on the same journey the next morning the problem was as bad as ever.Īrriving back at the workshop I reattached the scope and to my surprise the burn time was not that bad it’s worth noting that there is always a reduction in the burn time profile – especially when on load – and the current held steady at 8A. Famous last words!īy this stage it was just about home time so I took the opportunity to undertake a road test. “There, I knew it wouldn’t be that difficult,” I said. The effect was immediate – a good burn duration of approx 1.8 ms with a peak current flow of 8A, together with a crisp throttle response. Noting that a new coil had previously been fitted and then removed for the original coil module, I decided to replace it with a genuine OE replacement. The firing line voltage was high, confirming a high resistance in the ht firing line components. When testing the primary waveform pattern together with the current path profile I noted a poor burn time duration, on load, at no. The ignition system is a coil-per-plug type which uses a single cassette coil and allows easy access to a coil primary PicoScope evaluation. The Lambda signal, as expected, confirmed correct response throughout the fuelling range (see Fig 1). I focused on the acceleration load response, where I noted oxygen anomalies at/near the full load range – this confirmed ignition as the primary cause of the misfire. Starting my PicoScope evaluation, I took a look at the relationship between the Lambda and Map sensors as this would enable me to assess if the problem was an ignition or fuelling error. We always adopt the view that when dealing with spark ignition systems, in the absence of good ignition energy delivered to the plug electrode, good combustion simply can’t take place. This indicates a severe problem, with a risk of thermal damage to the catalyst. I began by checking the serial DTC’s – the MIL light was illuminated and flashing when the engine was running.
0 Comments
Read More
Leave a Reply. |