I am appealing to the collective to help me fix this dam Polo. CGPA engine code 1.2cyl beauty. The vehicle was initially presented for an MOT. The car failed its emissions test on high lambda reading (o2). I have a lot experience with these faults and quickly started on the diagnosis path I have trodden many times before. I read the code in the ECU which was P0171 and feeling pretty confident I was looking for an air leak started looking in this direction. (At this point out I noticed the engine could not hold revs at fast idle and kept creeping up then dying back) I found no sign of any leaks around the manifolds so I broke out the smoke tester and smoked the exhaust pipe and inlet manifold. No leaks were found so I capped off the EVAP pipe to the valve also the servo pipe but still no leaks were identified. Ok Russ lets go deep!! Looking at the Lambda sensor 1 shows at idle the lambda is switching frequently at idle but when the engine is taken off idle the lambda voltage drops through the floor and stays there. (Everything is telling me there is a massive amount of unmetered air entering the cylinder!)
Fuel pressure checked at both idle and 2500 rpm and no fault identified I then removed both manifolds to look for a mechanical fault and with the smoke tester found that all the exhaust valves and 2 of the inlets we not seated well at all. We removed the head and inspected but the exhaust valves were all bent. (At the time I thought this could be the cause of our wows but I now think they have been distorted due to a prolonged high build-up of heat caused by driver not noticing the fault in the drivability and the fact no MIL was on.)
Head was sent for pressure testing and after now faults being found other than the bent valves we rebuilt the head with 6 new exhaust valves and reseating the inlets.
We still have the same problem….
I can’t remember where I went from here, maybe I was delirious but at some I broke out the oscilloscope and started going super deep. One test that seemed to show the fault was the injector voltage/amp test. When the revs collapse the injector pulse cuts momentarily. I decided it is the ECUs way of giving up on trimming the fuel. I have sattempted to carry out a dynamic timing check by comparing the Crankshaft to the camshaft scope patterns but I cant interpret them accurately. can anyone help?
I have done lots of testing that I may have missed here but I’m out of ideas. I sure I’m missing something obvious but can’t for the life of me think what.[/