I posted some of this information in the Turbo forum, but thought I'd try to get some general information as well.

I have a 1997 Volvo 850 T-5 with 230,000 miles on it. For the past few months, it's been throwing a "Check Engine" light error. Originally the codes returned were a Slow O2 response code and a catalytic converter efficiency code.

I replaced the O2 sensor once and the CE light stayed on. I took the car to a highly recommended shop in town, where they dropped in a second O2 sensor (NAPA part). The Check Engine light stayed on -- slow O2 response. The Cat error vanished, but according to the shop, the car was refusing to run the Cat test altogether. It was "stuck," somehow, because of the O2 error.

Here's the thing, though -- when I drove the car on the old, bad O2 sensor, it was getting maybe 18 mpg. Once I replaced it, I started getting 23-25 mpg. So clearly it made a difference.

The shop then did a smoke test and told me there's a huge vaccuum leak from the Turbo. I've heard that it's possible to buy a metal fitted plate that would wrap around and seal this off, but since getting that work done is a major expense, I'm wondering if there's any way to tell if it's 100% the problem or not.

I need that light to go off so I can pass emissions, and clearing the code isn't good enough.


My question is this: Does the Volvo 850 throw an O2 code (P0133) because of a vacuum leak on a *Turbo?* The Catalytic converter code, if it matters, was P0420.

 

yes its not uncommon for a vacuum leak to throw an O2 sensor code. the theory is that the O2 sensor is trying to get the FI system to compensate for an incorrect mixture (caused by the vacuum leak) but can't quite get there before it goes out of "range" (ie maxes out its feedback voltage without correcting the mixture). I'd say if your smoke test was done correctly then its found the problem. You can try spritzing the area where you think the leak is with water to see if it gets sucked in by a crack (for areas other than the turbo waste gate you can use carb cleaner). Do you have any other issues, ie surging or the turbo cutting out? I'd suspect you would have other driveability issues (or turbo boost issues/loss of power) with a huge vacuum leak - Not sure about the metal plate idea... IMHO if something is broken like that its best to just fix the root cause. I suppose if you just need to pass a test you can try plugging the vacuum line upstream - but that may create other problems.

 

Hilariously, my Dad told me one way to patch a vacuum leak is to find a screw whose diameter matches the internal diameter of the vacuum hose and to screw it in.

I don't actually plan on trying this, because I don't know enough to pick the right pipe, but it amused me.

 

yep, I'll be hangin out with your dad having a beer watching you work :-)

Mostly vacuum leaks are caused by cracked rubber/plastic parts so you can trace a vacuum line from the wastegate (part of the turbo set up to blow off excess pressure) back to the other engine parts. There's a sticker on the front of the car or on the firewall that has a vacuum line diagram or you can find a picture on line to know the various parts that have lines going to them. Robert DIY also posted a helpful Youtube vid. The tricky leaks are the ones under the intake manifold (where the PCV components are), the vacuum tree (under the throttle cable rewind cover) and there's a line back to the Evap system. If you don't find a cracked/torn line then its possible its a torn diaphram in an actuator (less common but possible) - which means that part needs to be replaced.