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Is my O2 sensor broken?

Hi,

I have a 1997 Volvo 850 CD with 124,000kms on the clock.

Here's a bit of history. The car started producing a rattly/diesel-like engine sound whenever I accelerated. Took it to the mechanic who replaced the catalytic converter. The old one was breaking up apparently, and this solved the rattly/diesel-like engine noise. It was also at this time they discovered the oil was alarmingly low (had not been topped up for 10000kms) - my fault for not realising it consumed oil! Then, went on a 4000km roundtrip and topped up 0.5L of 15/40W Castrol oil every 500kms. Car was great for most of the trip, but by the time we got back, the car was very, very slow and shaking when moving from stationary. Once it got into about 2nd/3rd gear, it drove fine. Took it to the mechanic who discovered one of the relays to the engine had gone, and after replacing that, the acceleration has been back to normal. Then had to change the timing belt through regular wear and tear.

My problem now is that the fuel consumption has been, at least for the

18,000kms I have owned the car, very, VERY bad. I had a previous post on this, but just to recap, in 80% city driving, I am getting:

14.6L / 100km

16mpg (US gallons) 19.3mpg (Europe)

There has also been blue smoke coming from the exhaust only when accelerating shortly after the engine has been idle for a minute or so. This only started shortly after the timing belt change. When at cruising speed, there's no _noticeable_ smoke coming from the exhaust.

So this leads me to the question: Is my O2 sensor broken? Is there anything else likely to be causing the blue smoke and the poor fuel economy?

Regards,

Han.

Reply to
han_chung
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As with your fuel consumption, the need to add so much oil is _very_ bad.

Oil consumption often points to bad rings. Have you done a compression check?

Since 124 000 km is _nothing_ for this car, it may be that the previous owner(s) abused it.

Good luck.

cheers,

Henry

Reply to
Henry

Burning that much oil would probably kill both the cat and O2 sensor BUT what's causing the oil to be lost? That's the big issue. There IS something wrong with your car. It could be a simple maintenance item or it could be excessive engine wear (from abuse). IF that turns out to be the case then you can probably find a good second-hand motor for not too much cash depending on your location.

AJS

Reply to
AJS

There's your clue; whoever swapped the belt missed by a notch on one of the pulleys. You need to pull the cover off and check the marks on the belt against the marks on the pulleys; find the one that doesn't line up and correct it.

Gary

Reply to
Gary Heston

Hi Gary,

Thanks for your response. Why does a misplaced timing belt cause blue smoke and only after the car has been idle for a minute or so?

Regards,

Han.

Reply to
han_chung

Throwing the timing off can cause the cylinders to fire before the valves are open, causing excessive blowby. This would force oil through the PCV system, which will be burned off during cruising but could accumulate at idle. When starting out, this excess would be burned off, causing blue smoke.

If the cylinders are firing a bit late, there would be a slight loss in power, causing greater fuel consumption in normal driving. In any case, the fact that the problem appeared after a timing belt change indicates that theres' something wrong with the timing belt installation.

Gary

Reply to
Gary Heston

Hi Gary,

I should also mention that since the timing belt change, there has been the occasional repetitive squeak, it seems, everytime the belt spins a revolution. It tends to come and go, and sometimes is audible inside the car itself, and will happen whether the car is idle or accellerating. The noise appears to be coming from the vicinity of the timing belt.

In terms of fuel consumption, I have not noticed a drop, but I also did have catalytic converter problems (now replaced) before the timing belt change.

In light of all this, does this make your "misfiring cylinders" hypothesis even more likely?

Regards,

Han.

Reply to
han_chung

The squeak is probablly from either the tensioner pulley or the idler pulley. You should change them very soon before one or the other bearings seize then all the other questions about the motor will be moot.

Bob

Reply to
User

Translation: it will all be over except the crying.

Mike

Reply to
Michael Pardee

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