Engine: 2.5: 1997 V70 loss of power; no acceleration possible.

[giovannibianco]

Update: Compression test. I have been trawling the forum for similar problems and that gave me the idea to check fo mechanical problems, bent/burned valves, bad rings etc. So a compression test... the results are good, 190 +/- 5 PSI over all cylinders. So I rule out internal damage.

[SteveSarre]

Hi John

Can you get Torque to monitor the mass air flow reported by the MAF?
I suspect that that might not be reporting correctly.
Might as well monitor o2/lambda sensors at the same time.

But MAF is a fairly common problem.
Then, if you have a known good MAF obviously you could switch that in, and see what changes.

HTH
Steve

[Paul240480]

John is in Lyon, so his model will differ from ones released in UK at the same time.
That is why, I think, that his codes can be read using a reader and not flash codes?
It certainly sounds like it is in ‘limp mode’ . So to me , there must be another code.....
Maybe try with a different (read better) code reader.
I’ve got a cheapie Autel generic reader & an OBDsx (I think it’s called).
Last year my V70 ph2 went into limp mode
My Autel couldn’t find any codes.
Plugged the other one in, which connects to a lap top and bingo, misfire cylinder 3. New coil and sorted.
Just a thought.

[giovannibianco]

Hello Everyone,

Thanks for the replies... I've now made some effort to catch up with this problem...

So I have received my O2 sensor socket... Allowing me to check out the O2 sensors and exhaust/cat.
I removed the front, before catalytic convertor, O2 sensor. The tip is VERY white.
Then did the following tests:

1. Front O2 sensor removed... she now revs quite freely past 4,000 rpm and up to 5,000+ rpm.

2. Front O2 sensor replaced by bung. Goes back to the previous behaviour of not wanting to rev...

3. Front O2 sensor installed. Removed rear sensor. Still does not want to rev.

4. Rear sensor replaced by bung. Still does not want to rev.

Given these tests, it looks like the catalytic convertor may be blocked. As removing the rear O2 sensor should
release back pressure that may be built up in the mid or rear exhaust sections. This therefore can tell me whether it's the catalytic convertor or the mid-section muffler that is causing the problem.

I will make a test tomorrow where I will remove the front O2 sensor and take her for a quick drive locally to see if the power is back. Then repeat with the rear O2 sensor removed. This should tell me what I need to know.

Any comments/observations?

[giovannibianco]

Hello,

A update on my 1997 V70 problems... I at last have taken her for a quick drive locally to make a check. I removed the front O2 sensor to relieve the
back pressure, resulting in a rather "sporty" sound! Anyway, now she can
get to 60 km/h whereas before getting above 20 km/h was a struggle. The power is certainly not fully restored by any measure. I am assuming that with the from O2 sensor removed (disconected and sitting on my work bench) the engine is in some kind of "limp" mode? Once everything is cooled down I will put a bung into the O2 sensor hole and re-test.

I have in my possession a new catalytic convertor and exhaust middle section. May as well replace if it's got to be taken down anyway. Also new front and rear O2 sensors.

Fuel pressure at the rail is a solid 43 psi over the rev range.
Disconnecting the MAF gave no appreciable change in behaviour.
Engine check light is on... if it was not I would be worried I'm in the wrong car :-) ?

Cheers, John.

[giovannibianco]

Hello,

Update to my previous update... plugged the upstream O2 sensor hole with a bung and re-tested. Now she barely had any power to get outta the driveway and up the road (moderate slope). So there has to be an issue with the exhaust.

We have a car club at CERN, where I work, about 20 km away. There I have access
to full 4-post lifts etc. Need to drive her there next week. Either:

* I drive with front O2 sensor hole open and limp mode(?)

* or drill a few holes in the front of the cat and re-install the O2 sensor? Avoid limp mode?

* Other?

Cheers, John.

[giovannibianco]

Hello Everyone,

Update on the "blue bomber"... I changed the cat and exhaust last week and have made 100km-ish worth of tests. She's back to life better than ever! Pulls like a train and revs far better than before. Even no more engine light! We've had this car for seven(?) years or so and I've always
had a feeling that she's always been a bit "woolier" than our '94 850 (2.5 10v) that feels far zippier with more bottom end torque.

Maybe the cat has been in slow decline over the years and with a huge "collapse" at the end. She went from acceptable performance to barely struggling to get over 30 km/h. The definitive diagnosis step was to remove the front O2 sensor and notice the immediate ability to rev beyond
2500 rpm. OF course, driving without front O2 sensor was not very indicative as the engine was still not happy.

I installed the following for the exhaust:

WALKER: 18275
BOSAL: 290-517

I can confirm that the Bosal box givs a much "sportier" sound than the standard Volvo muffler that I removed (and have not junked yet as it may be in better shape than that on our '94 850).

Cheers, John.