'99 V70 2.4 NA - O2 sensors battle

fszczesniak · Post by **fszczesniak** » 04 Apr 2020, 15:24

No black smoke, more like white steam-like smoke that has fuel scent and not even always, depends on outside temperature

Post by **misha** » 04 Apr 2020, 16:13

No black smoke-NOT running rich....simple as that.
With front o2 reading at steady 0.98v it should have black smoke from the exhaust.
Steam is from condensation if it's cold outside.

fszczesniak · Post by **fszczesniak** » 05 Apr 2020, 02:12

What can cause such crazy readings then?

Post by **misha** » 05 Apr 2020, 02:50

fszczesniak wrote: 18 Mar 2020, 15:16 ...definitely vacuum hoses coming out from the intake manifold are in need of replacing...

Vacuum hoses,small leak from exhaust manifold to cat...between cat and rear o2.
Everything should be checked.

fszczesniak · Post by **fszczesniak** » 17 Apr 2020, 09:43

small update - S1B1 is linear in my case, figured it out only because of Vida (showing Lambda around 1.00 so good, I think?)
yesterday checked spark plugs as well, sockets were clean and dry but it seemed like they were a bit loose. Fixed the gaps as well to 0.030 inch - first test drive and the engine works quieter and smoother. Besides, didn't find any leaks in exhaust and vacuum systems.

AlexVolvo · Post by **AlexVolvo** » 16 Jul 2021, 19:08

Did you resolve this?

AlexVolvo · Post by **AlexVolvo** » 16 Jul 2021, 19:19

For reference,the front 02 is q wideband sensor (Linear Air Fuel Ratio) and works quite differently to the rear 02 which is a narrowband sensor, able to output from 0-1v and fluctuate betwen around 0.2v (lean) and up to 0.9v (rich).
The Front wideband does not produce it's own voltage but gets a signal supply voltage on two wires from PCM. The higher V is 3.8V, the lower is 3.4V (just need to confirm this as I need to change an O2 in the next month or so). You cannot see a difference or fluctuate on a volt meter, because I a wideband sensor signal to the PCM is an amperage fluctuation in the very low mA range ... on a Volvo roughly from -12mA (rich - yes widebands read rich in the negative range) to +0.60mAm (lean). You can only see this on a scantool and it often calculated and reported by the PCM to the scantool as a V even though this is not strictly what the PCM is reading. This is because of US OBDII rules requiring O2s to produce a voltage reading. Some scantools will give an Amperage reading. A dead wideband is usually due to bad wiring, open heater circuit, damaged/contaminate probe. The PCM will typically shut of the circuit if it is not reading correctly and log a code. Note that what I'm saying is for a four wide wideband sensor. A 5 wire wideband (on the turbo models) is slightly different again.