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.

 

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

 

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

 

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

 

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.

 

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

 

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.

 

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

 

Translation: it will all be over except the crying.

Mike