crosshair1 wrote: » This is the 1.9 engine right? Assume the fault code you have is P0171, system too lean. Possible causes for this particular code on this car are intake leak , pcv valve , MAF, O2 sensor. A s/h o2 sensor is not ideal as any hard knock renders them useless. I would not put any non genuine sensors on this as an attempt to remove the code, from experience it will not clear. The most common fault is the breather pipe from rear of rocker cover to PCV on manifold, this rots through allowing unmetered air be drawn into inlet, next to this is MAF, again non genuine will drive ok but P0171 will return believe me. BTW this should not be rocket science for your mechanic, It may involve a bit of time spent diagnosing the exact problem but should not turn into a "lets replace this and see what happens"
crosshair1 wrote: » Would treat a P0170 just the same its triggered by the fuel trims (ecu's own fuelling adjustment to remedy fault) reaching their limits. Basically the ecu is adding or reducing fuel to attempt to have an ideal air/fuel mix but has added/reduced as much as it can and still doesnt achieve control therefore triggering EML.
crosshair1 wrote: » If you remove the cover over the pollen filter, 3 clips (at the rear of the engine under front window) take out filter, remove 4 torx screws and remove housing you will see a pipe going into the top of the engine check that there is no crack/deterioration at either end of this.
shamwari wrote: » Regarding above comments re Lambda sensors, I agree fully with Crosshairs advice and diagnosis, especially regarding 2nd hand sensors not being a great way to go. As he says, some cars don't work right if you fit a replacement sensor, even if it is manufactured to OEM standard. Certain Honda's and Toyota's are a case in point. The original part from the main dealer is often the only way to go. I'm not sure if this applies to Beemers though. Also beware of Ebay, there's a lot of sh!te up for sale there in the guise of genuine parts.
crosshair1 wrote: » With the engine running remove the oil cap, is there a change to the engine note? Is the cap sucked back down?
crosshair1 wrote: » If the cap is difficult to pull away from the engine that means there is full vacuum in the engine and most likely is the pcv (valve) at fault
crosshair1 wrote: » What was the original fault with this car that determined that the o2 sensor was to be replaced. Has the o2 sensor voltage been checked by the mechanic in live data?
crosshair1 wrote: » From memory I dont think those parts are that much more expensive in the dealers here. If you dont have full vacuum to the engine then replacing the pcv is not necessary. The pipe I certainly would change. I'm not sure if its even viable to attempt to fix this without the necessary equipment, not just diagnostics. If this were in my workshop I would carry out the following Pressure test intake for unmetered leaks Pressure test exhaust for leaks before o2 sensor Vacuum gauge on inlet to confirm mechanical functions Scope the o2 voltage vs MAF Voltage to confirm that the o2 is capable of reacting and that the MAF voltage is within range. Replacing components based on the fault code alone I think at best would give 50% success, this is why a lot of mechanics would shy away from a p0170 as its definition doesnt refer to a specific part being faulty I'm not trying to knock you back on this but once Ive connected diagnostics and see a p0170 then thats pretty much as far as I can go with diags. and have to rely on other tests to determine the fault.
