2000 s70 n/a Help to analyse problem

Veilleuxpbd · Post by **Veilleuxpbd** » 23 Oct 2014, 20:49

I almost forgot; is the o2 b1 sensor ok or is it toast? I can't wrap my mind around this being a normal reading, yet I cannot find an answer on what a ''correct'' behavior would be.

Post by **northernlights** » 23 Oct 2014, 21:55

Based on your graph I would say the Bank 1 O2 sensor is done. The switching frequency on a new sensor will be more like 2x per second cycling between rich and lean. These are at best 80k mile items. You have a small amplitude at your switching point, and the sensor is slow. Both of these are indicitive of a worn out sensor.

The bank 2 sensor will last longer than bank 1, but it will be hard to tell the exact condition until after you replace the main O2 sensor. Either way bank 2 should read lower than bank 1.

Post by **mikealder** » 24 Oct 2014, 07:42

I have a 2000 V70 with the N/A engine, prior to changing the front Lambda sensor I used to get rev dips from time to time while stationary, you felt the engine almost stall down to around 500 RPM then recover, this wasn't down to the ETM as that has been repaired/ enhanced with the Sacer sensor. When the front Lambda probe packed up the main issue I observed was very poor fuel economy, once it was changed the economy recovered but ever since replacing the pre-cat probe the car hasn't dipped the revs while stationary.

Check for vac leaks as a start point, there is one difficult to get vac pipe on the end of the inlet manifold opposite end to the throttle body, this is part of the PCV system
There are three other vac lines that come from the front face of the inlet manifold near the ETM, one is the brake servo/ booster, the two smaller one goes to a sensors located on the fan shroud, the other which is a thin plastic line goes to the air filter housing, make sure these are all connected and don't have splits in them.

The car will have the Denso engine management system which also means the Volvo OEM supplied pre-cat Lambda probe is manufactured by Denso, it is often cheaper to get a Denso DOX-1419 probe than the Volvo one, the Denso DOX-1419 works fine in the N/A cars, mine has had one fitted for around two years, cost for a new one is around £100 (that's UK pounds) - Mike

Veilleuxpbd · Post by **Veilleuxpbd** » 26 Oct 2014, 18:22

I have looked and found a black vacuum line, coming from the air box, to nowhere, its end is glued. Where was it supposed to go? It is next to a white one that goes near the etm and fuel rail. As for the o2 sensor, I will definitely change that part thanks to your advice everyone. As for my random dips in rpm, I noticed that when I am in gear or neutral, if stationnary the rpms will never dip. When moving, they dip only when decelerating, AND (that's the new part) they dip to 500 rpm when reversing. When I reverse, the faster I go when I disengage the clutch, the worse it goes. I almost stalled the engine that way. Is it related to a vacuum leak or is it normal behavior considering the depression that occurs when the car leaves a space faster than air can fill in to atmospheric pressure?