tommylommykins

Hi all,

I have a 1.25 petrol engine MK6 fiesta.

It runs fine, except for between 1800 and 2000 RPM when I get a really strange judder/kangarooing when I'm accelerating. It happens in any gear.

I've plugged in my OBD2 reader, and I don't have any fault codes. I've tried some real-time logging, and that shows that the ignition advance and fuel flow both jitter a little when this jerking happens. The engine RPM readout also starts misreading upwards when this happens.

Anyone have any ideas what the root cause of this could be? It's had my head scratching for a while...

tommylommykins

I made a graph of the problem. Orange is speed and blue is engine RPM. I'm pretty sure that those spikes in the blue RPM readout means that there's something dodgy going on...

Does anyone know what might cause this? Dodgy crankshaft position sensor? dodgy electrics?

I'm a computer programmer by trade, so I'm a bit scared to try and replace any components... Does anyone know how much it might cost to get a new crankshaft position sensor installed?



Thanks!

tommylommykins

Not sure if anyone's reading this, but I thought I'd share an update.

I bought a a jack and some axle stands (yay). I managed to remove my old crankshaft position sensor. I cleaned it, tested its resistance, and replaced it. Everything seemed OK. The problem didn't go away

Having seen just how simple the sensor is, I'm struggling to believe that the sensor is faulty.

My next best guess is that there's a piece of magnetic debris sitting on my flywheel. Obviously I can't remove this without a lot of pain and effort, so I wonder what the next best thing is.

If it only has a small effect, I wonder if I could either add a resistor in the path of the sensor or add a washer to make it sit a little further away from the flywheel. I'm hoping that either of those will deemphasize whatever is causing bad readings.