Hi I have a 1995 volvo 850 gle non turbo 10 valve. We bought it without an o2 sensor and installed one reset the engine codes on port a2 then i checked the spark plugs and they were white with tons of crusty carbon that i cleaned off after driving the car and checking the plugs again they were a dry black colour. when the car is still cold it hesitates a bit when accelerating and I can hear popping (backfiring) but once it warms up it gets allot better but doesn't yet seem perfect. This morning I go start the car and put it in reverse and suddenly the lambda light is back so I checked the a2 error codes and I got a 512 and 521 when I tried cleaning the maf I used electronic cleaner it didnt make a difference and i noticed the plug only has 2 prongs maybe its actually a temperature sensor. Can anyone help me with the error codes and getting rid of this lambda light for good. Thanks

 

Hi and welcome to the forum.

These cars are 19 years old and the Volvo system is sensitive to the CEL light. You will have to reset the light to see if it returns and if it returns twice, fix the problem. Clean connections and make sure they are in good condition. If the connection is cracked or broken, replace it.

You can double check the fire order of the plugs to make sure they are connected properly. Also, the car is suppose to be fueled with 91+ octane.

 

Cleaned all connections checked fireorder and no difference as I said I reset the codes from a2 and the lambda disappeared but came back after some driving I checked a2 again and code 512 and 521 came back.

 

Let me Google that for you: https://www.google.com/#bav=on.2,or....ouble+code+512

512 is a fuel trim code, check for vacuum leaks at the intake manifold gasket and that hoses are connected and not split. Also that your fuel pressure is OK. If these all check out it could also be a bad mass air flow meter.

521 Front O2s Preheating circuit fault

 

Where did you get the new O2 sensor?

 

The 10V have no MAF . At the place where the MAF sits in the other engines there is the intake air temperature sensor. Together with the TPS the Fenix can compute the right mixture.
Due to the missing MAF these engines are not so "allergic" to air or vacuum leakeage as they 20V counterparts are, but a big "hole" will most probably offset the values until the O2 sensor throws the towel and gives you the finger
However as any other engine they do not like bad plugs, or insuficient fuel pressure.
Also check the leads and the induction coil (best to do this in the dark and carefully spray some water over these parts, if you see sparks get new ones).
Check also the distributor cap and the rotor inside, if you replace them get Bosch ones.
Also an important variable is the engine coolant temperature sensor. If the sensor gives false (but still plausible) values the Fenix will compute the wrong amount of fuel either too rich or the other way around, without posting DTC codes. This could explain your rough run when the engine is cold.

 

Turns out it was a bosch o2 sensor (zirconia only) which don't work with the 10 valve motors I needed an oem titania sensor with I got from volvo they wanted 350$$!!! It's made by ntk (ngk) I popped it in and it ran great and passed emissions no problem.