UK-POLOS.NET - THE VW Polo Forum

Hi,

I'm not a regular here but becoming one thanks to my Polo nearing 140k and would sure appreciate your help.

I have started to experience loss of power on motorways travelling around 70mph. Oddly lifting off the accelerator and back on again solves this but I think HP is down.

I have plugged in an ODBII which gave me codes for Cylinder 1 & 2 misfiring, system too lean, have for a while before this had a 'Bank 1 System below threshold' which I have been resetting (naughty I know). So with that, I took out spark plugs (felt a little loose for 2 & 3 and found carbon deposits on the rim (See picture below) which I cleaned, placed back in & put another two coils in.



Problem remains and now get open circuit errors on the cylinder 1 & 2 which is new.

The car generally runs fine, starts up, drives in 30 & 60 zones fine & not stalling; it just occurs at motorway speed and sometime on an incline.

Based on no spark in cylinder 1 & 2 too lean it suggests to me there may be a restriction in fuel indicating Fuel Filter or Fuel Pump. Fuel filter was last changed at 80K but the Pump is not showing typical signs that it is failing. Else, spark plugs?

Your thoughts would be most appreciated.

I'd think to give your self a clear starting point, you need to carry out a compression check on all cylinders, follow that with checking for crank<>cam static timing.

as well as the compression test suggested above
I would be looking toward the ( system too lean ) as it could be causing the misfire errors
System too lean can be caused by a vacuum leak when un metered air is being drawn in
I think you can test this by spraying carburetter cleaner around the intake pipework with the engine running and what your looking for is an increase in revs / idle as the cleaner gets drawn in through the leak
if your scan tool supports live data you may see that short term fuel trim is positive
This means the ecu is adding extra fuel to compensate for what it sees as weak / lean fuel mixture
When the ecu can't add any more fuel ( reached its limit of adjustment ) it then puts on the engine management light
After resetting the code the ecu will start to learn again and it may take 30 miles or so for the code to come back

Thats just my 2p worth
hope you get sorted

Thanks chaps, your feedback is very much appreciated and will certainly explore those routes and invest in a better reader. Will post back once diagnosed.