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Hi guys. I'm having uphill with a 1996 Toyota Noah with a 3s-Fe engine. Severe flat spot/hesitation on acceleration. Everything is pointing to a lean condition (the red trace in the images is my O2 sensor. Funny thing though, it's either lean or rich and I don't get an oscillation between lean and rich on the o2 signal no matter what scope setting I use. As soon as it hits rich this car takes off with no problem at all. This is a wasted spark system and I'm using an old ADC212 scope that unfortunately cannot invert cylinders 2
Fuel pressure is constant at 3bar and pinching the return hose (checking pump max output) take it up to 9 bar so no problem with the fuel pressure or pump. I tried pinching the return line to bring the pressure up to 4 bar and had the same flat spot/hesitation on snap throttle test.
Wave forms are showing lean (red trace is O2 sensor). Funny thing though the O2 is either at 100mv or 700mv, no oscillations in between. On the snap throttle the O2 is definitely lean and as soon as it rises to 700mv the engine takes off! Another thing I noticed is that if I keep the engine at a steady 3000rpm the O2 sensor drops to 100mv again.
Primary current traces are all good. Not sure what's happening though with the secondary voltage spikes. When I open up the scale on the scope it seems that only one in ten events is producing high voltage? If this were the case then why am I seeing a lean O2? I also realize that if the fuel is not being burnt I would also have oxygen coming through unburnt?
This has got me stumped! I'm new to oscilloscope diagnostics on petrol engines so please be kind!!!!!
Hardtopdr2 wrote: The injector wave form shows no pintle hump and drops way down which it should not pintle could be stuck shut.
Thanks HT. You know, I saw that, but on all four? Plus on the road, once the miss clears the car takes off and red lines no problem, but I think you're right. Anything is possible with the fuel we get in Africa! That could also explain the extreme lean and rich conditions in experiencing. O2 is either very lean or very rich, no in between.
Last edit: 3 years 8 months ago by Darren. Reason: Serious typo error
Yep if the injectors are sticking closed and getting stuck open from gunk in injector can cause your issue. Id say pull them out and run i jector cleaner through them with a fuel injector tester and a pressurised container feeding cleaner into it. Or just replace them and flush out the fuel rail and lines and replace the fuel filter. Id say you will be golden after that.
Problem solved! Carbon tracking on cyl 3 plug lead. I couldn't see this inverted wave forum on our old Pico ADC212 scope because there is no facility to invert the display. Managed to find an inductive pick up for our Snapon Modis and saw the fault immediately. The injectors got a clean at the same time which was probably not a bad thing. I did notice that the spray pattern improved dramatically when we were cleaning them out.
