Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Hi guys. I'm working on a Toyota Noah 2010 2az engine with a 4 wire COP and I had a classic shorting primary waveform on cylinders three. Initial ramp went straight up to about 3 amps initially and only then began to ramp. Bought a new coil and wouldn't you know it, same thing!! Swapped coils between cyl 1 & 3 and the fault stayed with cyl three. Compression is good and even on all four cylinders (10 bar). This has got me stumped. I measured current on the earth wire of all four cylinders. IGF and IGT signals are identical on all four coils, as are ignition and earth voltages.
How's the spark plug gap? Can you post the waveform?
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
The only other theory I was thinking about was that the coil was not fully discharged from the previous firing event (fouled plug, or high resistance in the combustion chamber due to rich air/fuel ratio, which I suspect because I have a rich O2 and maxed out neg fuel trim). My reasoning is that there is residual voltage in the coil and because of this a weaker CEMF to oppose current flow? Is that even possible?
I agree with Chad, this sounds like a plug issue. Gap is pinched shut, ceramic is cracked, like that. Try moving the plug to #2 or #4 and recheck your ramps.
Plugs were removed and inspected. Two were carbonated. Fitted a new genuine Toyota set and the same thing happened. Parts changing didn't work. Black soot on the plugs = rich condition (which is what STFT is telling us). I've removed the injectors but we don't have an injector test bench or a injector pulse driver. The nearest place that has one is a six hour drive away in Lusaka! Anyway, I'm taking them there to be tested and I'm hoping the guy I'm taking them to has good knowledge and equipment to give me a definitive result in the injectors. Coming back to the current ramp, it's starting to make sense to me that because of the rich condition/fouled plug the electrical energy is being stored in the coil from the previous firing event and we're getting and excessive straight up initial ramp because of less counter electromotive force?
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
I think such issues indeed would really call for a post of the waveform, also for future reference for others? Might also tell us things you missed here, might be driver issue, etc but hard to tell without the visual
Agreed, such topics should have a wave form and I apologise for my lack of a wave form guys. I'm running an old ADC212 Pico and I'm having difficulties saving an exportable wave form image. I'm running the Pico 5 software and I can save a graph view of the capture which works fine within the software but wherein I attempt to export the image the graph comes up with the traces so faint they cannot be seen. The other frustration I have is that the internet signal at our workshop location is not too good and I am unable to post directly off the Pico computer so a screenshot of the image doesn't work either. I've tried taking a photo of the screen with my phone but I get lines across the screen which makes the trade difficult to see as well. This is an issue I'm currently working on but it's taking longer than I expected but we will get there. Working in a third world country trying to deliver first world results certainly has its challenges and I apologise.
You could save the screenshots on a USB thumb drive then move it to your internet computer. That's about the easiest way to transfer files between PCs that aren't networked.
