1996 850 R loses power during accleration / misfire Topic is solved

[Clemens]

Hi guys!

After a couple relaxed and troublefree years in a 95 854 GLT I´m considering to buy a 96 850 R with around 180.000 miles on it (Turbo with automatic).

During the test drive where most of the car felt very good except for non serviced PCV tubes / oil trap and a heater core that smells a little like coolant (would have to be replaced someday soon).

That was until I kicked the pedal to the metal for the first time. THe car accelerated good, but then it surged power and it felt like a really hard shift combined with a lack of fuel or ignition.

Later I tried to do a full throttle start from the standstill and for the first 5-10 seconds it was hauling ass, but then the car stuttered really bad again, accompanied by a loud bang from underneath the floor panel (assuming . I then kept going at a decent speed but whenever accelerating really hard it would stutter again with more bang from what I believe is a major misfire in the exhaust. I´m sure it´s not the rev limiter cuz i tried how that feels with 1st gear locked. The rev limiter is way smoother that the power surge during acceleration.

The turbo seems fine and the boost meter goes almost all the way to the right.
When the turbo pressure increases I hear a hissing sound from the left a pillar area (below the dash or in front of the firewall - don´t know if that´s supposed to be)
The CEL didn´t come on (but it lights up with the ignition on so I suppose it´s working).
The automatic tranny shifts smoothly for a car of that mileage (the one in my 95 is pretty bad so I kinda believe to be able to judge that it´s alright).

I was thinking:
A) major problems from the turbo or related accessories
B) bad ignition that collapses under full throttle and turbo
C) strange electronics problem because the CEL won´t come on
D) uncommon automatic tranny issue (this doesn´t feel like an AT problem though, it´s more like losing a gear or a bad misshift in a manual tranny)
E) something caused by the kickdown switch cuz it only happens during really hard acceleration (but then, not right away but after a few seconds)

Any help would be appreciated cuz the car is pretty clean for 19 years of age, so I´d like to get it, but only with this issue fixed.

Thanks,
Clemens

[FLXC90]

sounds like boost control. Not necessarily major, but a thorough check of BCV, and lines. Volvo doesn't use a wastegate to dump pressure, they re-route air back around, so a hiss (or roar) is a leak, not normal operation. Check here and IPDs tech tips for some quick tips. Also, you may have blown a hose open or off. Especially if the previous owner hasn't been boosting like that for a while. (Volvo fun control system )

[Clemens]

Interesting ... the car had been parked for a few moths. so maybe I blew a hose off or something... will check on the boost control.

Thank you

[Clemens]

In case someone comes across this post in the future:

FLXC90 is probably right. The same problem in this thread was fixed by just reconecting the vacum lines to the BCV.

https://www.matthewsvolvosite.com/forums ... =1&t=37078

[Clemens]

So i drove the r for a few hundred miles now. Works very nice. Even under hard acceleration with the boost gauge 3/4 to the right (where the r max boost level should be).
The AT shifts alright. Not super smooth, but okay for 190.000 miles.

BUT when i floor the pedal (but only when i press the pedal reallY hard and suddenly) it still bogs a few times. After that it idles a bit rough in D but not in N.
So i wonder could that bogging issue be caused by a problem in the AT.
What exactly happens during kickdown?
Since the ATF hadn't been changed by the PO in the past 5 years i was wondering if that would help.

The turbo vacuum lines and hoses seem fine.

[FLXC90]

One thing that occurs during kickdown is an increase in line pressures. If something is holding after a kickdown event, then there may be varnish or debris in the valve body ports etc.. Not a trans specialist, sorry. On the other hand, either drain and fill or pump and fill trans fluid should definitely benefit your trans. Worst case it will highlight an already worn/damaged component, it will not cause any harm.

Also, as per the related posts, have you checked wastegate adjustment to optimize boost and control?

[Clemens]

Thanks for the hint with the increased line pressure. Might be that aftee sitting for months and maybe priir to that not javing been activated by the PO who was aged 65 there might be some debris blocking something. This would also explain why bwfore i bought it this bogging was really bad and now it seems to be less brutal.

I checked the vacuum lines and the wastegate actuator visually. The rod moves and the lines seem to be in in good shape and connected correctly.
i will go and drain the tranny fluid twice and see what happens.
i'd like to keep the pan on for now.

I'm undecided on adding tranny cleaner additive to the atf before draining it. This is probably good if one pressure flushes or sucks the system cuz all the cleaner additive is then removed from the system. If i only drain the fluid twice some cleaner stays in the system.

[erikv11]

There is no trans pan, just a plug. Drain and fill is the way to go, I would not recommend pressure flushing and for sure would stay far away from any trans cleaner additives.

[Clemens]

Well, thanks. Then i'll simply drain and drive a few times. The fluid had been changed within the last 10 years so nothing bad should happen...

[Sommerfeldt]

The turbo seems fine and the boost meter goes almost all the way to the right.

This seems a little worrying to me - even an HPT usually doesn't max out the gauge - I've never seen it at least, not even on my old T5-R. You might be overboosting for some reason.

- S